Thèses sur le sujet « Satellite interferometry »

The autonomous formation flying of multiple spacecraft to replace a single large satellite will be an enabling technology for many future missions. In this research, the current status of formation flying missions and technologies is determined, and the Darwin nulling interferometry mission, which aims to detect and characterise extrasolar planets, is selected as the research focus. Darwin requires high precision formation flying of multiple telescopes near the Sun-Earth L2 point. A comprehensive account of current research in astrobiology is presented which provides the motivation for a Darwin-type mission. Astrobiology is integral to the definition of formation manoeuvres and target identification. The system design issues associated with developing a higher resolution, Planet Imager mission are also explored through a preliminary mission design. Relative dynamics models for satellite formation flying control in Low Earth Orbit (LEO) and L2 are developed and methods of incorporating the Earth oblateness perturbation (J2) into the equations of relative motion to improve model fidelity are investigated. The linearised J2 effect is included in the Hill equations in time averaged and time varying form. The models are verified against the Satellite Tool Kit (STK) numerical orbit propagator, and applied to optimal control system design and evaluation for formation keeping tasks. The ‘reference orbit’ modelling approach applied in LEO is applied to the development of a new formation flying model at L2. In this case, linearised equations of motion of the mirror satellites relative to the hub are derived and performance evaluated for different initial conditions. These and other higher order models are compared to STK. The linearised model is applied to controller design for station keeping and formation manoeuvring tasks suitable for a Darwin-type mission, and the role of the model in developing controllers for a load levelling guidance system is explored.

This thesis for a PhD by Publication attempts to demonstrate the author’s contribution towards the development of terrestrial satellite radar interferometry (InSAR) for geohazard applications between 1995 and 2016. The author’s role is shown by reference to six peer-reviewed articles, and five ‘documents of influence’ that demonstrate key pieces of work that helped progress the application of InSAR technology. The work included ranged from the first InSAR-related contract to be funded by ESA, through the introduction of InSAR into the CEO’s Disaster Management Support project that influenced both the Space Charter for Major Disasters and the Global Monitoring for Environment and Security programme, to the widespread exploitation and standardisation of InSAR seen in the Terrafirma and FP7 PanGeo projects. The author’s contributions have resulted in a wider-spread InSAR awareness and expertise, direct support to the European Space Agency’s flagship application of the time, the inclusion of InSAR within Copernicus services, and support to the mission-design of Sentinel-1a/b.

Synthetic aperture radar interferometry (InSAR) is a technique that enables generation of Digital Elevation Models (DEMs) and detection of surface motion at the centimetre level using radar signals transmitted from a satellite or an aeroplane. Deformation observations can be performed due to the fact that surface motion, caused by natural and human activities, generates a local phase shift in the resultant interferogram. The magnitude of surface deformation can be estimated directly as a fraction of the wavelength of the transmitted signal. Moreover, differential InSAR (DInSAR) eliminates the phase signal caused by relief to yield a differential interferogram in which the signature of surface deformation can be seen. Although InSAR applications are well established, the improvement of the interferometry technique and the quality of its products is highly desirable to further enhance its capabilities. The application of InSAR encounters problems due to noise in the interferometric phase measurement, caused by a number of decorrelation factors. In addition, the interferogram contains biases owing to satellite orbit errors and atmospheric heterogeneity These factors dramatically reduce the stlectiveness of radar interferometry in many applications, and, in particular, compromise detection and analysis of small-scale spatial deformations. The research presented in this thesis aim to apply radar interferometry processing to detect small-scale surface deformations, improve the quality of the interferometry products, determine the minimum and maximum detectable deformation gradient and enhance the analysis of the interferometric phase image. The quality of DEM and displacement maps can be improved by various methods at different processing levels. One of the methods is filtering of the interferometric phase.However, while filtering reduces noise in the interferogram, it does not necessarily enhance or recover the signal. Furthermore, the impact of the filter can significantly change the structure of the interferogram. A new adaptive radar interferogram filter has been developed and is presented herein. The filter is based on a modification to the Goldstein radar interferogram filter making the filter parameter dependent on coherence so that incoherent areas are filtered more than coherent areas. This modification minimises the loss of signal while still reducing the level of noise. A methodology leading to the creation of a functional model for determining minimum and maximum detectable deformation gradient, in terms of the coherence value, has been developed. The sets of representative deformation models have been simulated and the associated phase from these models has been introduced to real SAR data acquired by ERS-1/2 satellites. A number of cases of surface motion with varying magnitudes and spatial extent have been simulated. In each case, the resultant surface deformation has been compared with the 'true' surface deformation as defined by the deformation model. Based on those observations, the functional model has been developed. Finally, the extended analysis of the interferometric phase image using a wavelet approach is presented. The ability of a continuous wavelet transform to reveal the content of the wrapped phase interferogram, such as (i) discontinuities, (ii) extent of the deformation signal, and (iii) the magnitude of the deformation signal is examined. The results presented represent a preliminary study revealing the wavelet method as a promising technique for interferometric phase image analysis.

Synthetic aperture radar interferometry (InSAR) is a technique that enables generation of Digital Elevation Models (DEMs) and detection of surface motion at the centimetre level using radar signals transmitted from a satellite or an aeroplane. Deformation observations can be performed due to the fact that surface motion, caused by natural and human activities, generates a local phase shift in the resultant interferogram. The magnitude of surface deformation can be estimated directly as a fraction of the wavelength of the transmitted signal. Moreover, differential InSAR (DInSAR) eliminates the phase signal caused by relief to yield a differential interferogram in which the signature of surface deformation can be seen. Although InSAR applications are well established, the improvement of the interferometry technique and the quality of its products is highly desirable to further enhance its capabilities. The application of InSAR encounters problems due to noise in the interferometric phase measurement, caused by a number of decorrelation factors. In addition, the interferogram contains biases owing to satellite orbit errors and atmospheric heterogeneity These factors dramatically reduce the stlectiveness of radar interferometry in many applications, and, in particular, compromise detection and analysis of small-scale spatial deformations. The research presented in this thesis aim to apply radar interferometry processing to detect small-scale surface deformations, improve the quality of the interferometry products, determine the minimum and maximum detectable deformation gradient and enhance the analysis of the interferometric phase image. The quality of DEM and displacement maps can be improved by various methods at different processing levels. One of the methods is filtering of the interferometric phase.
However, while filtering reduces noise in the interferogram, it does not necessarily enhance or recover the signal. Furthermore, the impact of the filter can significantly change the structure of the interferogram. A new adaptive radar interferogram filter has been developed and is presented herein. The filter is based on a modification to the Goldstein radar interferogram filter making the filter parameter dependent on coherence so that incoherent areas are filtered more than coherent areas. This modification minimises the loss of signal while still reducing the level of noise. A methodology leading to the creation of a functional model for determining minimum and maximum detectable deformation gradient, in terms of the coherence value, has been developed. The sets of representative deformation models have been simulated and the associated phase from these models has been introduced to real SAR data acquired by ERS-1/2 satellites. A number of cases of surface motion with varying magnitudes and spatial extent have been simulated. In each case, the resultant surface deformation has been compared with the 'true' surface deformation as defined by the deformation model. Based on those observations, the functional model has been developed. Finally, the extended analysis of the interferometric phase image using a wavelet approach is presented. The ability of a continuous wavelet transform to reveal the content of the wrapped phase interferogram, such as (i) discontinuities, (ii) extent of the deformation signal, and (iii) the magnitude of the deformation signal is examined. The results presented represent a preliminary study revealing the wavelet method as a promising technique for interferometric phase image analysis.

In this thesis, I use synthetic aperture radar (SAR) and radar altimeter data to make new observations of Antarctic and Greenland ice sheet grounding lines. I use ERS SAR data acquired between 1992 and 2011 to map the Petermann Glacier grounding line on 17 occasions using quadruple difference interferometric SAR (QDInSAR). Over the 19-year period, the grounding line position varied by 0.5 km, on average, with no significant trend over time. Although tidal forcing explains a fraction (34 %) of the movement, localised variations in the glacier thickness could explain it all were they to alter the glaciers hydrostatic balance as they advect downstream – a hitherto unconsidered possibility that would reduce the accuracy with which changes in grounding line position can be detected. Next, I developed a new technique for detecting grounding lines using differential range direction offset tracking (DRDOT) in incoherent SAR data. I then applied this technique to a sequence of 11 TerraSAR-X images acquired in 2009 over Petermann Glacier. The DRDOT technique is able to reproduce the shape and location of the grounding line with an estimated lateral precision of 0.8 km and, although this is 30 times poorer than QDInSAR, provides a complementary method given the paucity of coherent SAR data. Finally, I developed another new method for detecting the grounding line as the break in ice sheet surface slope computed from CryoSat-2 elevation measurements. I then applied this technique to map grounding lines in the sectors of Antarctica buttressed by the Filchner-Ronne, Ekström, Larsen-C, and Amundsen Sea ice shelves. The technique is able to map the grounding line to within 4.5 km, on average, and, although this is far poorer than either QDInSAR or DRDOT, it is computationally efficient and can succeed where SAR-based methods fail, offering an additional complementary approach.

Includes bibliographical references.
Synthetic Aperture Rada Interferometry (InSAR) is a relatively new remote sensing technique, which can be used to derive precise topographic height change information over large areas. It is a technique which has been used in a great variety of situations, from the topographic mapping of Venus to the detection of subtle ground deformations due to earthquakes and mining subsidence. The InSAR technique involves using the phase information inherent in radar images to extract elevation and elevation change information. The process requires very careful co-registration of a pair of complex images of the same scene, followed by the multiplication of the one image by the complex conjugate of the other. In this manner, a phase difference image, or interferogram is generated, in which subtle differences in the distances from the two imaging sensors to the ground are mapped, thereby making it possible to generate a height model of the ground surface. An extension to the InSAR technique, is that of difference image, or interferogram is generated, in which subtle differences in the distances from the two imaging sensors to the ground are mapped, thereby making it possible to generate a height model of the ground surface.

The Rutford and Evans Ice Streams together drain over 150,000 km2 of the West Antarctic Ice Sheet, a marine ice sheet with much of its bed below sea level. Ice streams make up only 13% of the Antarctic coastline, but are responsible for 90% of the discharge across the grounding line, where the ice starts to float. The Rutford and Evans Ice Streams were investigated using the remote sensing method of interferometry, which uses the phase difference between successive Synthetic Aperture Radar (SAR) satellite images to derive displacement in the line-of-sight (LOS) direction of the satellite and topography, which can be separated with further processing. The grounding zones of both ice streams were mapped from clearly defined changes in vertical tidal motion visible in the interferograms. The Rutford grounding zone is dominated by a central pinning point, and the Evans grounding zone has a complex shape so that for much of the main trunk of the ice stream the east side is grounded and the west side is floating. The tidal signal for each ice stream was reconstructed, and the tidal ranges of the Rutford and Evans grounding zones are more than 6 m and 5 m respectively, both well above average for Antarctica. Vertical displacement observed in both single and double difference interferograms correlated well to changing tidal height. The width of the grounding zone modelled using an elastic beam was close to the observed grounding zone width for both ice streams. Successful differential interferometry relies on the validity of the Constant Velocity Assumption (CVA), which states that interferograms differenced to derive topographic phase must contain the same displacement phase. However, due to the large tidal ranges at the grounding lines both ice streams, this assumption, which would be better termed the Constant Displacement Assumption (CDA), was violated to an extent which may be unprecedented in the literature. The Rutford Ice Stream reached velocities of approximately 400 m a-1 at its grounding line between 1992 and 1996, and the Evans Ice Stream appears to have decreased in speed from 750 m a-1 in 1992 to 540 m a-1 in 1996. This would have a significant effect on mass balance. The behaviour of this ice stream up to the present day clearly requires further investigation.

This thesis considers the use of Interferometric Synthetic Aperture Radar (InSAR) for surveying temporal fluctuations in the velocity of glaciers in the Arctic region. The aim of this thesis is to gain a broader understanding of the manner in which the flow of both land- and marine-terminating glaciers varies over time, and to asses the ability of InSAR to resolve flow changes over timescales which provide useful information about the physical processes that control them. InSAR makes use of the electromagnetic phase difference between successive SAR images to produce interference patterns (interferograms) which contain information on the topography and motion of the Earth's surface in the direction of the radar line-of-sight. We apply established InSAR techniques (Goldstein et al., 1993) to (i) the 925 km2 LangjÖkull Ice Cap (LIC) in Iceland, which terminates on land (ii) the 8 500 km2 Flade Isblink Icecap (FIIC) in Northeast Greenland which has both land- and marine-terminating glaciers and (iii) to a 7 000 km2 land-terminating sector of the Western Greenland Ice Sheet (GrIS). It is found that these three regions exhibit velocity variations over contrasting timescales. At the LIC, we use an existing ice surface elevation model and dual-look SAR data acquired by the European Remote Sensing (ERS) satellite to estimate ice velocity (Joughin et al., 1998) during late-February in 1994. A comparison with direct velocity measurements determined by global positioning system (GPS) sensors during the summer of 2001 shows agreement (r2 = 0.86), suggesting that the LIC exhibits moderate seasonal and inter-annual variations in ice flow. At the FIIC, we difference pairs of interferograms (Kwok and Fahnestock, 1996) formed using ERS SAR data acquired between 15th August 1995 and 3rd February 1996 to estimate ice velocity on four separate days. We observe that the flow of 5 of the 8 outlet glaciers varies in latesummer compared with winter, although flow speeds vary by up to 20 % over a 10 day period in August 1995. At the GrIS, we use InSAR (Joughin et al., 1996) and ERS SAR data to reveal a detailed pattern of seasonal velocity variations, with ice speeds in latesummer up to three times greater than wintertime rates. We show that the degree of seasonal speedup is spatially variable and correlated with modeled runoff, suggesting that seasonal velocity changes are controlled by the routing of water melted at the ice sheet surface. The overall conclusion of this work is that the technique of InSAR can provide useful information on fluctuations in ice speed across a range of timescales. Although some ice masses exhibit little or no temporal flow variability, others show marked inter-annual, seasonal and even daily variations in speed. We observe variations in seasonality in ice flow over distances of ~ 10 km and over time periods of ~10 days during late-summer. With the aid of ancillary meteorological data, we are able to establish that rates of flow in western Greenland are strongly moderated by the degree of surface melting, which varies seasonally and secularly. Although the sampling of our data is insufficiently frequent and spans too brief a period for us to derive a general relationship between climate and seasonality of flow, we show that production of meltwater at the ice surface and its delivery to the ice bed play an important role in the modulation of horizontal flow speeds. We suggest that a similarly detailed investigation of other ice masses is required to reduce the uncertainty in predictions of the future Arctic land-ice contribution to sea level in a warming world.

Landslides display a wide variety of behaviors ranging from slow persistent motion to rapid acceleration and catastrophic failure. Given the variety of possible behaviors, improvements to our understanding of landslide mechanics are critical for accurate predictions of landslide dynamics. Recent advances in remote sensing techniques, like satellite radar interferometry (InSAR), now enable high-resolution spatial and temporal measurements that provide insight into the mechanisms that control landslide behavior. In this dissertation, I use InSAR and high-resolution topographic data to identify 50 slow-moving landslides in the Northern California Coast Ranges and monitor their kinematics over 4 years. These landslides have similar mechanical properties and are subject to the same external forcings, which allows me to explore geometrical controls on kinematics. Each landslide displays distinct kinematic zones with different mean velocities that remain spatially fixed. Because these deformation patterns are sensitive to subsurface geometry, I employ a mathematical model to infer landslide thickness and find that these landslides exhibit a highly variable thickness and an irregular basal sliding surface. Time series analysis reveals that each landslide displays well-defined seasonal velocity changes with a periodicity of ∼ 1 year. These velocity variations are driven by precipitation- induced changes in pore-water pressure that lag the onset of rainfall by up to 40 days. Despite significant variations in geometry, I find no systematic differences in seasonal landslide behavior. To further explore how stress perturbations control landslide motion, I develop a mechanical model that reproduces both the displacement patterns observed at slow-moving landslides and the acceleration towards failure exhibited by catastrophic events. I find that catastrophic failure can only occur when the slip surface is characterized by rate-weakening friction and its spatial dimensions exceed a critical nucleation length that is shorter for higher effective stresses. These model simulations support my conclusions from the remote sensing analysis but also provide insight into the long-term evolution of landslides. This dissertation includes both previously published and unpublished co- authored material.

Slope processes are a many-sided issue, related to many interconnected factors, which need different approaches to be fully understood. Different investigation methods needs different observation scales depending on their limits and data availability. Classical field tools (such as GPS stations, piezometers and inclinometers) and geological surveys represent an effective approach to landslide investigations also allowing a sub-surface knowledge; but data collection start only from the beginning of survey. Air-borne and space-borne remote sensing techniques allow both, small and large scale analysis. Air-borne data are available from the 50 but their acquisitions are discontinuous in time; space-borne SAR (Synthetic Aperture RADAR) data are available from 1992 (ERS-1 mission) until now, providing twenty years of information about land and object displacements but their application in landslide analysis need an in depth study. This research aimed to investigate the potential for satellite A-DInSAR (Advanced Differential Interferometric Synthetic Aperture RADAR) techniques in landslide identification and characterization, in addition to airborne or terrestrial investigations and geological field surveys. I worked mainly on applicability and interpretation of A-DInSAR techniques at different scale: regional scale (Agno Valley), large slope scale (Rovegliana), and single slope scale (Prezzo landslides). The satellite remote sensing techniques called A-DInSAR includes Small Baseline Subset (SBAS) (Berardino et al., 2002) and Persistent Scatterers (PSInSAR) (Ferretti et al., 2001) algorithms. The main advantages of these techniques are: i) availability of 20-years of data and possibility of reconstruct displacements dataset; ii) application on small and large observation scale. The main limits of advanced DInSAR techniques are temporal decorrelation and geometrical distortions. Temporal decorrelation is due to changes of electro-magnetic response of objects with time caused by atmospheric phenomena or anthropic changes or vegetation growth. Satellite look angle of 23.3° (for used ERS and ENVISAT images) and right side-looking acquisitions mode, are the responsible for geometric distortions effects: layover and shadow. These effects, together with aspect and inclination of slopes, need to be taken into account before starting an investigation of mountainous area, because slope instability processes could be located in area affected by layover or shadow effects. Another issue to consider in landslide analysis with A-DInSAR techniques is the measurement of displacement along the radar-target line of sight that provides a 1D displacement velocity. The 3D velocity problem (W-E, N-S, vertical directions) can be solved using both, ascending and descending images. Aiborne remote sensing methods, LIDAR (LIght Detection and Ranging) and optical images photo-interpretation permit to trace the outline of slope instabilities, to classify their characteristics (state of activity, frequency, etc.) and to identify geological and tectonic settings of landslide prone areas. But, their discontinuous acquisitions lead to low precision in displacement measurements. Terrestrial remote sensing techniques (laser scanning, Ground-Based-InSAR, photogrammetry, GPS station) permit large scale investigations, seeking out details of the instability phenomena; they represent a useful complement to conventional field mapping and rock mass discontinuity characterization. These methods are a useful approach because allow i) investigating vertical rock face, which is no detected by satellite InSAR or airborne techniques and ii) the construction of detailed 3D model and 3D displacement data of the phenomena. In contrast they need long and hard-working data collection. In the end, geological-geomorphological and geotechnical field surveys allow to verify and complete the data collected using techniques described before, sometime discovering new important details such as geological settings predisposing to landslide. Regional scale analysis illustrates a feasibility study on the limits of A -DInSAR applicability in landslide phenomena analysis. Layover and shadow maps (LS map) of Agno basin were combined with morphological characteristics (slope and aspect) and land use data. The Agno Valley is located in the NW sector of Vicenza Province. The valley in characterized by gentle relief (only NW part present high relief over 1500 m and slope over 40°), the mean altitude is 600-700 m. The main morphometric features are easterly aspect and slope values between 10° and 30°. Rotational/translational slides and slow flows are the common landslide types. The two LS maps, one for ascending and one for descending acquisition mode were created. These maps show the areas affected by geometric distortions, which are devoid of RADAR information and are unusable for instability processes investigations (17.8% of total Agno Valley area for descending track and 11% for ascending one). Combining ascending and descending LS maps, only 1.3% of Agno Valley is simultaneously affected by LS distortions; therefore these areas cannot be investigated through interferometric techniques (using ERS-1/2 and ENVISAT images with incidence angle of 23.3°). Focusing on relationship between aspect/slope factors and visible area, it has been analysed slope and aspect index (normalized invisible areas divided by normalized visible areas for each class) for both ascending and descending acquisition mode. When the index is greater than one, the number of invisible pixels is greater than the visible ones. The results show that slope values greater than 30° are the main morphometric limit for the application of InSAR techniques, whereas the aspect class that hindered the use of InSAR methods on instability characterisation is the East one for descending orbit and West ones for descending track. Comparing land use data and LS maps, the results show that 44% of visible area fall into woody area, the 11% is part of urban zone and 22% fall within grass land class. Therefore a big percentage of visible pixels fall into "problematicà" land use classes for interferometric processing: woody and grass land areas have low density of PS and SBAS data, due to the sparse presence of scatters. Regarding Italian Landslide Inventory, the 18.2% of mapped landslides are hit by layover effect in descending track, whereas the 10.2% is “not visible” in ascending images and only 1.4% of known instable phenomena is totally “invisible” to both descending and ascending track. These results show a good inclinations of Agno Valley to be investigated by interferometric way. For the large slope analysis, time-series displacement datasets derived from SBAS and PS interferometric processing of ERS and ENVISAT images (ground pixel resolution of 25x25m) were analysed to evaluate the real contribute of these two innovative techniques and to determine the state of activity of landslide phenomena affecting Rovegliana area (North sector of Agno Valley). Several time-consuming interferometric processing were conducted to find out the best interferometric-procedure parameters to process mountainous and vegetated areas such as the test areas. Rovegliana slope is mainly affected by rotational, translational and shallow movements that involve mainly the quaternary deposits and fractured rocks and no displacement data are available. Due to quite large extension of total area affected by landslides (4 Km2), and to high density of vegetation, field detection methods (eg. GPS, laser scanning) and the aerial ones, are expensive and time-consuming. PS and SBAS data, obtained from intererometric processing, were very helpful in this morphologic context. In fact, the presence of scattering houses on the entire slope, facilitated the unwrapping step of interferometric processing, although the presence of vegetated areas. PS data allowed the identification of new landslides, not previously recognized in the Landslide National Inventory. PS data also helped following geological-geomorphological investigations and historical aerial optical images analysis finalised to the delimitation of these new instabilities. Moreover, satellite DInSAR data helped to defined the state of activity and, in some cases, the return time of landslides. The large slope scale case of Rovegliana demonstrated that interferometric techniques can help in the identification and characterisation of the landslide processes in those areas where: i) vegetation is strongly present, ii) the extension of instable area is too large for classical methods (GPS or laser scan) iii) a displacement dataset is absent or deficient, and iv) geologic or morphologic evidence are lacking. At the single slope analysis, Prezzo landslides (Giudicarie Valley, Trento) were analysed via PS and SBAS techniques, LIDAR data and field surveys. The interferometric processing were computed using ERS and ENVISAT ascending images because the LS map of descending images highlights layover effect on Prezzo area. Thus, the capability of interferometric techniques to gain 3D displacement data is null. But the ascending LOS is quasi-parallel to landslide movement, so the assumption that LOS velocity data detect the real displacement can be done and it was supported by the final results. Moreover, ERS ascending dataset has many corrupted and unprocessable images, and available images (19) were no sufficient to compute PS processing. Both, PS (2004-2010) and SBAS (1995-2010) data distributions, show a clear identification of the unstable area on Prezzo village, where the houses represent good scatterers, but outside the village, where trees and grass land prevail, data density is very low. In the case of Prezzo landslide GPS and interferometric data were compared to demonstrate the good capability of PS and SBAS to detect the displacement velocity and to identify different displacement zones. The high resolution of LIDAR data improved the geological, geomorphological and structural field surveys allowing a complete analysis of the landslide process. The parallel use of different remote sensing methods supported by field data, demonstrate that A-DInSAR data can improve a reliable identification and delimitation of landslide areas and the history of its displacements. Satellite remote sensing techniques allowed to overcome the usual drawbacks of conventional field detection and classical monitoring methods (e.g. GPS, laser scanning, optical photo, LIDAR), especially when used over small and medium areas (up to 5-6 km2). Furthermore, the twenty years of interferometric data allow the definition of long displacements dataset permitting to evaluate temporal evolution of instabilities, also when a monitor system is lacking or incomplete. But in some cases, for example high velocity phenomena or steep slope location, terrestrial remote sensing detection is needed to outpace the intrinsic limits of satellite InSAR and air-borne techniques. Therefore a simultaneous use of satellite, airborne, terrestrial and field data can lead to a complete landslide identification and characterizations reducing the costs and the spending-time of the analysis
Nel presente lavoro sono riportati i risultati sulle potenzialità di applicazione e sull'interpretazione dei dati interferometrici, ottenuti attraverso le tecniche avanzate DInSAR (Differential Synthetic Aperture RADAR Interferometry), ai fini dell’analisi della franositàa diverse scale d’indagine. Le immagini SAR dei satelliti ERS 1, ERS 2 ed ENVISAT, sono state processate tramite le tecniche Persistent Scatterers (PS) e Small Baseline Subset (SBAS) utilizzando il software SARscape. Alla scala del bacino È stato eseguito uno studio di fattibilitàper individuare i fattori che limitano la possibilità di ottenere informazioni dal trattamento interferometrico dei dati SAR. L’area analizzata È la Val d’Agno, una valle situata nella parte nord-occidentale della provincia di Vicenza, caratterizzata da pendenze medie comprese tra 20° e 30° e da versanti principalmente orientati verso i quadranti orientali. Le aree affette da distorsioni geometriche (layover e shadow) sono state combinate con i fattori morfometrici (pendenza ed esposizione) e con le carte di uso del suolo, per capire quali fattori limitano l’applicazione delle tecniche interferometriche. I risultati mostrano che le aree del bacino in cui non È possibile ottenere informazioni sono molto limitate e l’acquisizione di dati SAR È ostacolata principalmente da elevati valori di pendenza. Confrontando le frane presenti nel catalogo IFFI (Inventario dei Fenomeni Franosi d’Italia), con le aree in layover, si ottengono risultati favorevoli all’utilizzo delle tecniche DInSAR nell’area della Val d’Agno. Alla scala del versante sono stati analizzati i risultati ottenuti dall'analisi PS ed SBAS delle immagini sia ascendenti che discendenti dei satelliti ERS e d ENVISAT al fine di valutare l’evoluzione temporale e lo stato di attività dei fenomeni franosi nell'area di Rovegliana, situata nella parte nord-orientale della Val d’Agno. Le tecniche interferometriche hanno individuato molti target in movimento, anche se l’area è molto boscata e ciò ha permesso di indentificare nuovi fenomeni franosi, oltre a quelli presenti nel catalogo IFFI. Le informazioni derivanti dai dati interferometrici, congiuntamente all'analisi geologica-geomorfologica e alla fotointerpretazione delle immagini aeree ottiche, hanno agevolato la delimitazione delle instabilità. Le serie degli spostamenti derivanti dai processamenti PS ed SBAS dello stack di immagini SAR ha reso possibile la definizione dei tempi di ritorno di alcune frane. Soprattutto i dati SBAS sono stati utili a questo scopo poichè presentano una minore oscillazione dei valori di spostamento rispetto ai dati PS e quindi permettono l’individuazione di periodi di stasi e di accelerazione del movimento franoso. Alla scala locale, l’area studio di Prezzo (valle delle Giudicaria, Trento), si È dimostrata ideale per l’integrazione delle metodiche DInSAR con i dati LIDAR, la fotointerpretazione ed i rilievi geologici. La frana di Prezzo È un movimento traslazionale studiato dal Servizio Geologico della Provincia di Trento fin dal 1999 con GPS e mire ottiche. Si sono potuti confrontare i dati di spostamento PS con i dati del monitoraggio terrestre scoprendo una quasi perfetta correlazione tra le velocità dei due metodi e validando cosÌ i dati interferometrici. La frana di Prezzo È soggetta a fenomeni di layover in modalità discendente, perciò i dati di velocità calcolati con l’analisi PS si riferiscono a spostamenti lungo la LOS ascendente. La corrispondenza dei valori È dovuta al fatto che il movimento di frana È quasi parallelo alla direzione della LOS e perciò quasi tutto il movimento reale È misurato dall’analisi interferometrica. Questo a sottolineare che la buona riuscita di un’analisi interferometrica differenziale dipende da molti fattori tra cui la relazione tra movimento, angolo di vista del satellite e direzione LOS. Inoltre, gli scatteratori individuati dall’analisi PS, identificano molto bene l’area instabile caratterizzata da velocità comprese tra 20 e 5 mm/anno, da quella stabile (dato sempre confermato dalla rete GPS e da quella ottica). Nella comprensione della dinamica delle aree instabili la frequente mancanza di dati relativi all’evoluzione temporale ed anche spaziale degli spostamenti rappresenta un limite per la loro caratterizzazione. L’analisi interferometrica delle immagini RADAR satellitari offre il grande vantaggio di fornire vent’anni (dal 1992 ad oggi) di dati relativi agli spostamenti delle aree instabili. I limiti imposti dalla stessa tecnica (decorrelazioni temporali e spaziali, misure lungo LOS), dalla morfologia del territorio (aspect e slope) e dalla tipologia di movimento (velocità), ostacolano la sua applicazione, che deve essere valutata di volta in volta, in funzione dei limiti sopra brevemente elencati. Per questo motivo, il dato interferometrico satellitare non sostituisce le altre metodologie di telerilevamento o le indagini in sito, ma opportunamente integrato ad esse, aumenta le potenzialità e le possibilità di una corretta analisi dei processi d’instabilità dei versanti

Laser Interferometer Space Antenna est une mission de l'Agence Spatiale Européenne visant à mesurer les ondes gravitationnelles dans le domaine millimétrique. Trois satellites en formation triangulaire autour du Soleil s'échangent des faisceaux lasers. Les variations de distances entre masses d'épreuve, dues aux ondes gravitationnelles, sont mesurées au picomètre près. Plusieurs algorithmes de réduction des bruits instrumentaux qui contaminent les mesures sont utilisés avant l'extraction des signaux gravitationnels.Afin d'évaluer la performance de ces algorithmes, nous étudions la manière dont les bruits instrumentaux apparaissent dans les mesures, ainsi que leurs résidus après calibration. Un outil de simulation numérique flexible, destiné à générer les mesures de manière réaliste, permet de valider ces résultats. En effet, LISANode propage les séries temporelles de bruit entre les satellites et sur les bancs optiques, jusqu'aux phasemètres et aux ordinateurs embarqués. Il calcule aussi la réponse aux ondes gravitationnelles. Par ailleurs, LISANode permet de générer les combinaisons Time-Delay Interferometry exemptes de bruit laser, ainsi que la calibration pour les bruits d'horloge.Malheureusement, ces bruits ne disparaissent pas totalement si l'on tient compte des imperfections instrumentales et numériques. Nous étudions en particulier l'impact de la déformation de la constellation, ainsi que du traitement des données en vol. Nous modélisons le couplage déformation-filtrage et proposons une technique permettant de réduire cet effet. En outre, nous proposons une méthode de calibration exacte des bruits d'horloge. Les simulations permettent de valider ces résultats, et confirment la possibilité de réduire les bruits dominants aux niveaux requis.Nous considérons aussi les techniques d'apprentissage automatique pour discriminer les artéfacts instrumentaux et les signaux gravitationnels courts. Une étude analytique montre un couplage différemment dans les mesures, et les premières expériences suggèrent que certains réseaux de neurones peuvent distinguer ces deux types de signaux
The Laser Interferometer Space Antenna is a European Space Agency mission that aims to measure gravitational waves in the millihertz range. Three spacecraft are placed in a quasi-equilateral triangular formation whose barycenter trails the Earth on its heliocentric orbit. Laser beams are exchanged to monitor pico-metric variations between the test masses due to gravitational waves. Because various instrumental noise sources couple to the measurements, several data processing techniques are used to reduce them before we can extract gravitational-wave signals.To study these noise-reduction algorithms, we propose a realistic instrumental model. We investigate how the main noise sources appear in the measurements and work out their residuals in almost noise-free combinations. To validate these results, we develop a flexible numerical simulation tool that aims to generate realistic measurements: LISANode propagates noise time series between the spacecraft and in the optical benches, all the way down to the phasemeters and the on-board computers. It also computes the response to gravitational waves. LISANode is capable of executing the main noise-reduction algorithms, including the computation of Time-Delay Interferometry laser noise-free combinations, as well as clock-calibrated combinations.As we account for instrumental and numerical imperfections, noises do not exactly vanish in the final combinations. In particular, we study the performance hit of the constellation flexing and the on-board data processing on the laser-noise reduction. We model the flexing-filtering coupling and propose a technique to mitigate this effect. Moreover, we derive exact clock-noise calibration expressions. Simulations are used to validate these results and confirm that the dominant sources of noise can be reduced to the required levels.We also investigate machine-learning techniques to discriminate between instrumental glitches and transient gravitational signals. Analytic studies show that both appear differently in noise-free combinations and experiments suggest that some neural networks are capable of distinguishing between them

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.
Includes bibliographical references (p. 125-128).
Our study investigates interferometric SAR (InSAR) post-processing height retrieval techniques. We explore the possible improvements by adding a third satellite to the two already in orbit, and examine some potential uses of this setup. As such, we investigate three methods for height retrieval and compare their results with the original 2-satellite method. The first approach is data averaging; a simple method that extends from the results obtained using the 2-satellite method. The 3 sets of data obtained per sampling look are grouped into pairs, and the 2 statistical best pairs are selected to be averaged, producing a better estimate of the digital elevation map (DEM) height. The second approach is the unambiguous range magnification (URM) method, which seeks to ease the reliance on phase unwrapping steps often necessary in retrieving height. It does so by expanding the wrapped phase range without performing any phase unwrapping, through the use of different wrapping speeds of the 3 sets of satellite pairings. The third method is the maximum likelihood estimation technique, an asymptotically efficient method which employs the same phase expansion property as the URM to predict the closest phase estimate which best fits most (if not all) of the data sets provided.
(cont.) Results show that for a handful of flyover looks, the data averaging method provides for an efficient and non-computationally intensive method for improving retrieved height results. This method can also help eliminate the need of GCPs in height retrieval, though such performance is limited by the presence of noise. The maximum likelihood method is shown to be asymptotically favorable over the data averaging method, if given a large number of flyover looks. The URM method performs worst, because it depends on the shortest baseline, which is most sensitive to noise, for unwrapping. Results are entirely simulation-based, using the engineering tool Matlab Version 6.1. Single- and multiple- trial simulations are compared for 1-dimensional interferograms only. In most cases, the root-mean-square error will be used as the metric for comparison.
by Wallace D. Wong.
S.M.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: ELECTRICAL ENGINEERING in the Faculty of Engineering at the Cape Peninsula University of Technology 2014
The thesis reports on the evaluation and comparison of various signal processing algorithms for estimating the direction of arrival (DOA) of a high frequency (HF) beacon signal from a CubeSat in Low Earth Orbit (LEO). The DOA of the HF beacon signal is expressed in terms of the two angles, azimuth ( α ) and elevation ( ). The azimuth and elevation angles of the received HF signal are calculated from the phase differences between signals observed at three elements of an L-shaped crossed-loop antenna array. The algorithms which were evaluated are the Zero Crossing (ZC), Cross Correlation (CC), Fast Fourier Transform (FFT) and Cross Power Spectral Density (CPSD) algorithms. A theoretical analysis was done to demonstrate that the phase differences at the radio frequency (RF) of the beacon are propagated to the baseband signals. The algorithms were thus tested using simulated baseband signals as would be derived from the RF signals intercepted by the three elements of an L-shaped crossed-loop antenna array. Gaussian noise with a given signal-to-noise ratio (SNR) was added to the simulated baseband signals. The algorithms were implemented in MATLAB. The criteria for the selection of the best algorithm were accuracy and speed. The standard deviation (SD) of the azimuth and elevation errors was used to measure the performance accuracy of each algorithm, while the computational time for a given number of samples and runs was used to express the speed of each algorithm. First the ZC, CC, FFT and CPSD algorithms were evaluated for various SNR values, and compared with respect to SD of the azimuth and elevation errors. The analysis of the simulations demonstrate that the FFT and CPSD algorithms outperform the ZC and CC algorithms by estimating the DOA with a small SD of errors even at the low SNR of 0 dB, where the noise amplitude is the same as the signal amplitude. The ZC algorithm estimates the DOA with a large SD of error at low SNR due to multiple ZC points occurring during the same cycle. The ZC algorithm breaks down when the SNR decreases below 35 dB. The accuracy of the ZC algorithm depends on the method by which the ZC points are detected. The CC algorithm breaks down when the SNR decreases below 10 dB. The CPSD and FFT algorithms break down when the SNR decreases below – 20 dB. However, at a high SNR of 40 dB and above, all the algorithms estimate the DOA with a SD of error smaller than 1˚ for the azimuth and elevation. Next, the ZC, CC, FFT and CPSD algorithms were compared with respect to computation time. The FFT was found to be the fastest algorithm. Although the CPSD and the FFT algorithms reach the same accuracy in the estimation of the DOA, the FFT was selected as the optimum algorithm due to its better computation time. Recommendations are made regarding the implementation of the proposed algorithms for real signals from the HF direction finding (DF) array. At the time of submission of this thesis, such signals were not yet available.

Imaging distant objects at a high resolution has always presented a challenge due to the diffraction limit. Larger apertures improve the resolution, but at some point the cost of engineering, building, and correcting phase aberrations of large apertures become prohibitive. Interferometric imaging uses the Van Cittert-Zernike theorem to form an image from measurements of spatial coherence. This effectively allows the synthesis of a large aperture from two or more smaller telescopes to improve the resolution. We apply this method to imaging geosynchronous satellites with a ground-based system. Imaging a dim object from the ground presents unique challenges. The atmosphere creates errors in the phase measurements. The measurements are taken simultaneously across a large bandwidth of light. The atmospheric piston error, therefore, manifests as a linear phase error across the spectral measurements. Because the objects are faint, many of the measurements are expected to have a poor signal-to-noise ratio (SNR). This eliminates possibility of use of commonly used techniques like closure phase, which is a standard technique in astronomical interferometric imaging for making partial phase measurements in the presence of atmospheric error. The bulk of our work has been focused on forming an image, using sub-Nyquist sampled data, in the presence of these linear phase errors without relying on closure phase techniques. We present an image reconstruction algorithm that successfully forms an image in the presence of these linear phase errors. We demonstrate our algorithm?s success in both simulation and in laboratory experiments.

This research presents the design of a two-element radio interferometer capable of performing complex correlation. With the development of sophisticated radio astronomy instruments, particularly in South Africa, there is a need to develop an affordable educational instrument which can be used to demonstrate the fundamental concepts of radio interferometry to university students. The mass production of satellite TV equipment has resulted in relatively sensitive radio frequency (RF) equipment such as parabolic reflector dishes and low-noise block down-converters (LNBs) being available at significantly reduced costs. This served as the front-end of the interferometer which was used to observe the sun between 10.70 GHz - 12.75 GHz (RF). The LNB then down-converted these to an intermediate frequency (IF) between 0.95 GHz - 2.15 GHz. The LNBs were modified to make use of a common 25 MHz reference, which ensured that the observed fringes were only as a result of the source's geometric time delay. A power detector was also designed since the adding interferometer architecture was chosen. This power detector included the Analog Devices LT 5534 power detector integrated circuit (IC) and a Teensy 3.6 microcontroller. The calibrated power detector could detect signals as weak as - 60 dBm and showed less than 21 mV error in output for input signals in the range [- 50 dBm, -30 dBm]. The modified LNBs experienced issues, in particular the presence of a spurious LO signal, which distorted initial observations of the sun. This was resolved by the design and manufacture of narrowband hairpin filters and quarterwavelength stub filters which were used to isolate the IF band between 1.05 GHz - 1.15 GHz (corresponding RF between 10.80 GHz - 10.90 GHz). This also improved the interferometer's resolution. A series of filter-integrated Wilkinson power dividers and branchline couplers were designed to filter and further separate signals into in-phase and quadrature-phase (I-Q) components - these were required for complex correlation. The integrated quarter-wavelength stub filter and Wilkinson power divider achieved a maximum amplitude imbalance of 0.13 dB and phase imbalance of 0.9◦ between output ports. The integrated quarter-wavelength stub filter and branchline coupler achieved a maximum amplitude imbalance of 0.13 dB and phase imbalance of 91.1◦ between output ports. These results closely agreed with the simulated performance. First light was observed on the 5th December 2020 when the sun was successfully detected using the coherent two-element interferometer along a 1.1 m baseline. Other tests included using the observed fringe phase to verify the physical baseline. A theoretical baseline of 1.11 m was calculated for a physical baseline of 1.3 m indicating an error of less than 0.2 m. The sun's fringe frequency and amplitude was also observed for varying baselines - the sun was resolved along a 3 m baseline. Finally, full-system observations of the sun were conducted. These included observing the sun's cosine and sine fringes, which indicated that the analogue complex correlator was operating correctly. Thus, the primary goal of this project had been fulfilled. Specifically, developing a low-cost, educational two-element radio interferometer capable of detecting the sun.

We report the results of high-angular-resolution observations that search for exozodiacal light in a sample of main sequence stars and sub-giants. Using the "jouvence" of the fiber linked unit for optical recombination (JouFLU) at the center for high angular resolution astronomy (CHARA) telescope array, we have observed a total of 44 stars. Out of the 44 stars, 33 are new stars added to the initial, previously published survey of 42 stars performed at CHARA with the fiber linked unit for optical recombination (FLUOR). Since the start of the survey extension, we have detected a K-band circumstellar excess for six new stars at the similar to 1% level or higher, four of which are known or candidate binaries, and two for which the excess could be attributed to exozodiacal dust. We have also performed follow-up observations of 11 of the stars observed in the previously published survey and found generally consistent results. We do however detect a significantly larger excess on three of these follow-up targets: Altair, v And and kappa CrB. Interestingly, the last two are known exoplanet host stars. We perform a statistical analysis of the JouFLU and FLUOR samples combined, which yields an overall exozodi detection rate of 21.7(-4.1)(+5.7) %. We also find that the K-band excess in FGK-type stars correlates with the existence of an outer reservoir of cold (less than or similar to 100 K) dust at the 99% confidence level, while the same cannot be said for A-type stars.

Questo lavoro di tesi analizza il fenomeno della subsidenza e delle sue cause naturali e antropiche tramite analisi di dati di interferometria satellitare raccolti nel periodo dal 1992 al 2011 con un periodo centrale mancante dal 2000 al 2002. Lo studio si è concentrato nell'area di Bologna, principalmente nella zona di conoide del fiume Reno. L’elaborato ha previsto una prima fase di analisi in ambiente GIS dei dati che sono stati gentilmente concessi dalla Regione Emilia-Romagna. A questo scopo sono state realizzate serie di mappe della velocità media di deformazione e di grafici di serie temporali di spostamento, acquisiti da un insieme di dati di immagini SAR. In particolare, ho elaborato un set di dati SAR acquisiti dai sensori ERS (European Remote Sensing Satellite), ENVISAT (Environmental Satellite) e RADARSAT.
Successivamente si è passati ad una analisi delle serie temporali per quanto riguarda lo spostamento e la variazione di velocità nei tre archi temporali relativi ai tre satelliti di cui avevamo i dati. Si è inoltre analizzata la variazione della subsidenza in relazione alla variazione della falda e si sono fatte alcune ipotesi interpretative sul fenomeno.
Il lavoro, attraverso l’analisi dei movimenti del suolo, basata su risultati interferometrici, dati del suolo e osservazioni geologiche, ha quindi lo scopo di confermare la causa antropogenica (effetto superficiale dovuto al sovrasfruttamento delle falde acquifere) e di valutare l’evoluzione del fenomeno negli ultimi 15 anni.

Le Propulseur à Effet Hall est un moteur sans grille, dans lequel un champ magnétique radial confine les électrons d'un plasma formé entre deux cylindres coaxiaux diélectriques. La chute de la conductivité électronique qui en résulte permet l'établissement d'un champ électrique axial pour extraire les ions. La relativement faible poussée (100 mN) et la forte impulsion spécifique (vitesse des ions éjectés de 20 km/s) rendent le propulseur bien adapté aux tâches de maintien sur orbite des satellites ou de petits transferts d'orbite. L'étude porte sur la modélisation des phénomènes physiques dans le propulseur associée à une étude expérimentale, plus limitée, et destinée à valider ou compléter les modèles. La modélisation est basée sur une description des phénomènes de transport des particules (électrons, ions, neutres) en champs électrique et magnétique croisés. Un modèle développé au CPAT a été complété et utilisé pour chercher les conditions optimales de fonctionnement, en particulier l'étude de la configuration magnétique des moteurs à Effet Hall existants. De plus, nous avons développé un modèle pour étudier de nouveaux concepts de moteurs à Effet Hall, en particulier un moteur à Effet Hall à Double Etage, dans lequel on cherche à contrôler séparément la génération du plasma et l'accélération des ions. La partie expérimentale a consisté à utiliser des techniques de diagnostics plasma (interférométrie de Fabry-Pérot) permettant de mesurer la distribution du champ électrique dans le système, résultant de la présence du plasma et des tensions appliquées aux électrodes. Les mesures ont été effectuées sur le moyen d'essai PIVOINE installé à Orléans. La confrontation systématique des résultats expérimentaux et de simulation a permis de mieux définir les possibilités et les limites du modèle et d'en améliorer ses capacités prédictives
Hall Effect Thrusters (HETs) are gridless ion engines where a magnetic field barrier is used to impede the electron motion toward the anode and generate a large electric field that provides collisionless ion acceleration. The thrust is about 100 mN and the specific impulse of HETs is in the range 1600-2000 s (i. E. The velocity of ejected xenon ions is on the order of 16-20 km/s). The thrust and the specific impulse of standard Single Stage HETs are well adapted to the missions of orbit correction and station keeping. The goal here is to model the physical phenomena occurring in such a thruster, and, in correlation with experimental studies, to validate and/or improve the assumptions of the model. The model describes the transport of the electrons, ions, and neutrals in crossed electric and magnetic fields. The model developed at CPAT was extended and used to identify conditions for optimal operation of the thruster, with particular attention to the influence of the magnetic field distribution on the thruster operation. In addition, we developed a model to study new thuster concepts such as a Double Stage Hall Effect Thruster, where ionization and acceleration are accomplished in two stages. The experimental study involved using specific plasma diagnostics (Fabry-Perot Interferometry) in order to measure the electric field distribution in the thruster. Measurements were made at the PIVOINE test facility in Orléans. Systematic comparisons between experimental results and simulations allowed us to define more clearly the limits of the model and to improve its predictive ability

Scopo di questa tesi è la produzione di una serie di mappe di deformazione del suolo o della copertura superficiale del terreno mediante l'utilizzo di una tecnica di monitoraggio territoriale da satellite denominata Interferometria SAR. Tale tecnica si colloca nell'ambito del Telerilevamento a sensori attivi. Le mappe di spostamento sono state prodotte per quattro casi di studio, due riguardanti eventi sismici (terremoto del 2009 a L'Aquila in Italia e terremoto del 2003 a Bam in Iran) e due relativi al movimento di deriva conseguente allo scioglimento dei ghiacciai alpini (ghiacciaio dell'Aletsch in Svizzera) e delle calotte polari (ghiacciaio David-Drygalski in Antartide).

Analyses of ground displacements can help to define the evolution of areas affected by instability phenomena and identify their triggering factors. To this end, Synthetic Aperture RADAR (SAR) satellite data can be used to collect direct measurements of superficial deformations in instability-prone areas. Results from remote sensing analyses can be then compared with outcomes from numerical simulations, and in particular with displacement or velocity fields, to validate numerical modeling and eventually recalibrate the simulation of instabilities, predisposing and triggering conditions. Numerical simulations allow reproducing slope behavior under some hypotheses but their accuracy is strongly connected to the amount of available input data. Most of the required parameters can be set based on reasonable assumptions that consequently can be verified through classical field tools and geological survey or remote sensing techniques. Direct or remote sensing techniques can be used to characterize and monitor ground deformation phenomena, and particularly to identify surface displacements. These information can be used to verify the suitability of numerical model predictions and the adequacy of preliminary hypotheses. An innovative approach could consider a surface displacement map, as the starting point to re-create a model of instability phenomena. This application requires precise velocity data characterized by an adequate resolution, depending on the phenomenon analyzed. Recently this method was applied to earthquakes with satisfying results (Wright at al., 2006). This work is aimed to determine which is the contribution of SAR satellite data in investigating instabilities phenomena, in particular landslides and sinkholes. This methodological approach was tested in different conditions to understand its applicability and how to optimize the results overcoming some of the observed limits. Satellite remote sensing techniques have shown to lead to accurate large-scale surface displacement mapping. Specifically “Interferometric Synthetic Aperture RADAR” (InSAR) technique allows to measure accurate land displacement. Furthermore, not only deformation but even the evolution of displacements can be estimated, combining InSAR information from a large number of SAR images and analyzing changes on the signal phase. This technique is defined D-InSAR (Differential Interferometric SAR) and PS InSAR (Ferretti et al., 2001) and SBAS techniques (Berardino et al., 2002) represent the main methodology proposed. But D-InSAR techniques have some limits of applicability. For example, due to high RADAR viewing angles, the current space-borne systems can detect only a fraction of the horizontal component of the movement. In fact not every geometrical configurations and slope exposition can be surveyed. Further problems are connected with the presence of dense vegetation. In these situations amplitude can be exploited to identify surface deformations (Casu et al., 2011). Applying the above mentioned techniques it is possible to observe deformation patterns and surface movements. Comparing displacement obtain from monitoring stage with results from numerical modeling, let to understand if numerical prevision is satisfying and the evolution of deformations is correct. The contribution of SAR data in numerical simulation of ground deformations was tested in landslide, subsidence and sinkhole - prone areas, located in the piedmont sector of North-Eastern Italian Alps and in the Jordanian coast of the Dead Sea. The first case study is Val Maso landslide, located in Valli del Pasubio municipality, which was triggered by an exceptional flood event occurred in November 2010. A back stability analysis was carried out to evaluate the geotechnical properties of the involved materials. Then, parameters from back analysis were used in a uncoupled seepage and slope stability analysis of the area behind the main scarp to forecast the effects of hydrological conditions due to different rainfall depths, i.e. to identify the minimum rainfall threshold for triggering the retrogression of the phenomenon. Some more information about this phenomenon have been searched, analysing a stacking of RADAR satellite images. Because of the dense vegetation and the aspect of the area, outcomes of PS and SBAS DInSAR technique were not satisfying. That is why SAR data were analyzed concentrating on amplitude changes of the signal instead on studying the phase. A stack of nine COSMO-SkyMed images, acquired over the 2010 event, were used. Amplitude changes were evaluated. Results showed it is possible to detect the effect of ground deformations from the data analyzed and to define the boundary of the landslide. The second case study is Cischele landslide, located in Recoaro Terme municipality, which caused severe damages on the buildings and on the Provincial street after the rainfall event of November 2010. This phenomenon is related to a reactivation of a instability whose behavior seems to be connected to climatic conditions. Data obtained from field and laboratory analyses were used on the creation of a numerical model. Ground displacements of the slope were evaluated analyzing data obtained from PS available for Cischele area, obtained processing SAR images acquired by ERS and ENVISAT satellites, from May 1995 to May 2000 and from September 2004 to June 2010, respectively. Ground velocity and displacements are measured along the line of sigh of the satellites. Only information obtained from descending orbits are available. Furthermore, InSAR images acquired by COSMO-SkyMed satellites over the event were analyzed. SBAS techniques was applied. Interferograms were generated using InSAR images and a 90 meters resolution Digital Elevation Model (DEM), SRTM DEM. 14 descending images were available from April 2010 to September 2012. Unfortunately, variation in surface condition between two different acquisitions produces loss of coherence. This effect is strongly connected to the presence of vegetation in the area. It was possible to overcome this problem through an accurate calibration of the filtering parameters, extending the coverage of the final displacement map. Results showed a maximum velocity component of 12 mm/year. Finally, DInSAR techniques were applied to investigate sinkholes affecting the Jordanian coast of the Dead Sea. The Dead Sea is a hyper saline terminal lake located in a pull-apart basin, which is one of the major components of the Jordan Dead Sea Transform fault system. Most of the area is characterized by highly karstic and fractured rock formations that are connected with faults. Karstic conduits extend from the land into the sea. Since the 1960s, the Dead Sea level is dropping at an increasing rate: from about 60 cm/yr in the 1970s up to 1 m/yr in the 2000s. From about the mid-1980s, sinkholes appeared more and more frequently over and around the emerged mudflats and salt flats. Strong subsidence and landslides also affect some segments of the coast. Nowadays, several thousands of sinkholes attest that the degradation of the Dead Sea coast is worsening. The deformation analysis is focused on Ghor Al Haditha area, located in the South-Eastern part of the lake coasts. SAR data acquired by three different sensors, ERS, ENVISAT and COSMO-SkyMed were processed. 70 ERS images from 1992 to 2009 and 30 ENVISAT images from 2003 to 2010 were processed. SBAS technique were applied to define surface velocity and displacement maps. Because of the resolution of these sensors, consisting on 25 m2, it was possible to clearly define areas affected by subsidence but the single sinkholes could not be detected because of the small size of each punctual event, that is generally varying from few meters to a hundred meters diameter. Furthermore, SBAS was applied to 23 COSMO-SkyMed SAR satellite images from December 2011 to May 2013. The high resolution of these data (3m x 3m) and the short revisiting time allowed to have precise information of the displacement of punctual sinkholes beyond the overall subsidence of the coast. A specific sinkhole was considered to understand its temporal evolution. On the basis of the results from D-InSAR processing, a simplified analytical model was implemented. Vertical and horizontal components of the surface displacement field obtained from analysis of SAR images have been used as input data to derive geometric parameters of the source and in particular to estimate the volumetric strain of the phenomenon. Position, dimension and mechanism were obtained. The gained experience proved that space-borne SAR data allow to obtain important information about the dynamics of instability phenomena, which degree of precision depends on several factors, as vegetation density and surface velocity. The applicability of D-InSAR methods in different conditions was tested to obtain useful information to re-create the phenomena through numerical modeling. When rapid displacements overcome the maximum detectable surface velocities between two consecutive SAR acquisitions and changing in land cover produces a complete coherence loss, the amplitude of the signal can be analyzed instead of the phase. In the Val Maso landslide, a rapid mapping of surface deformation was possible, providing important hints to manage post-event emergency situations. Despite the dense vegetation in Cischele area, SBAS technique could assess a component of the landslide displacement, through an accurate calibration of some processing parameters. Thanks to the flat morphology of the site and the almost absent vegetation covering, analysis of sinkholes in Jordan Dead Sea coast gave precise information about ground deformation and helpful data to model a sinkhole and to define its geometry and volume reduction. In these favorable conditions, SAR data allow one to predict the occurrence of geological instabilities, characterize their extension, model their evolution and define an early warning system to prevent catastrophic events.
L’analisi degli spostamenti superficiali del terreno permette di ottenere importanti informazioni sull’evoluzione di un fenomeno di instabilità geologia e identificarne i fattori di innesco. A questo scopo, i dati RADAR ad apertura sintetica (SAR) satellitari possono essere utilizzati per raccogliere misure indirette relativamente alle deformazioni superficiali di aree affette da dissesti geologici. I risultati ottenuti tramite tecniche di telerilevamento SAR possono poi essere confrontati con i risultati di simulazioni numeriche: il raffronto tra campi di spostamento e velocità consente di validare e calibrare il modello numerico. Le simulazioni numeriche sono probabilmente lo strumento più diffuso per la riproduzione un dissesto sotto specifiche ipotesi, la cui esattezza è fortemente connessa alla quantità di dati di input disponibili. Spesso molti dei parametri necessari a costruire un modello devono essere stabiliti attraverso ragionevoli assunzioni, che possono essere verificate grazie a misure sul campo e monitoraggi con tecniche classiche, o attraverso tecniche di telerilevamento. Un diverso approccio, applicato nella creazione di un modello, consiste nel considerare una mappa di spostamenti superficiali quale punto di partenza per modellare un fenomeno di instabilità e le caratteristiche della sorgente. Tale approccio necessita della disponibilità di precisi valori di velocità di spostamento, ad una risoluzione spaziale adeguata al fenomeno che si sta analizzando. Il presente lavoro è finalizzato a determinare il contributo dei dati SAR satellitari nello studio dei dissesti geologici, con particolare riferimento a frane e sinkholes. L’approccio metodologico è stato utilizzato in diverse condizioni per capirne l’applicabilità e ottimizzarne i risultati ottenuti, superando alcuni dei limiti del dato SAR. Le tecniche di telerilevamento RADAR satellitare, ed in particolare la tecnica InSAR (Synthetic Aperture RADAR Interferometry), considerano le variazioni di fase tra il segnale trasmesso e la componente retrodiffusa che torna al ricevitore, e restituiscono accurate mappe di spostamento superficiale su larga scala. Tra l’altro è possibile stimare non solo le deformazioni, ma tutta l’evoluzione degli spostamenti, utilizzando informazioni derivanti da diversi interferogrammi ottenuti da numerose immagini SAR, combinandoli ed analizzando i cambiamenti di fase del segnale. Queste tecniche sono definite D-InSAR (Differential Interferometric SAR) e i principali algoritmi proposti in quest’ambito sono denominati PS InSAR (Ferretti et al., 2001) ed SBAS (Berardino et al., 2002). Ma le tecniche D-InSAR hanno delle limitazioni nella loro applicazione: possono rilevare solo una componente dello spostamento complessivo; non tutte le geometrie sono visibili al satellite ed è quindi importante valutare l’esposizione dell’area che si analizza; anche la presenza di fitta vegetazione genera delle limitazioni. In questi casi è possibile utilizzare l’ampiezza del dato, anziché la fase, per identificare superfici soggette a deformazioni (Casu et al., 2011). Le tecniche menzionate sono state applicate a tre casi reali: • due frane manifestatesi nella zona prealpina della Provincia di Vicenza nel 2010; • subsidenza e sinkholes che affliggono la costa Giordana del Mar Morto. Entrambe le frane analizzate, la frana di Contrada Cischele e la frana di Val Maso, sono state innescate da un evento di pioggia eccezionale che ha colpito la Provincia di Vicenza nell’autunno 2010. La frana che ha interessato Contrada Cischele, nel Comune di Recoaro Terme, è caratterizzata da velocità di deformazione contenute, dovute alla riattivazione del versante in frana in stretta connessione con gli eventi di pioggia e quindi l’innalzamento della falda. La frana si è manifestata causando danni alle abitazioni presenti, alla strada Provinciale ed al muro di contenimento che la delimita. Grazie alle indagini in situ e alle prove di laboratorio effettuate sui materiali è stato possibile riprodurre un modello di stabilità globale del versante. L’analisi del dissesto con dati SAR è avvenuta inizialmente attraverso la valutazione dei dati PS storici nell’archivio del Ministero dell’Ambiente, verificando la presenza di spostamenti precedenti all’evento del 2010. Successivamente è stata applicata la tecnica SBAS utilizzando 14 immagini COSMO-SkyMed acquisite a cavallo dell’evento piovoso. La presenza di vegetazione nel versante, che è causa di una decorrelazione temporale tra i dati, ha reso particolarmente complesso il processamento. Attraverso un’attenta calibrazione dei parametri di filtraggio dei dati è stato possibile definire il campo di spostamenti nell’area indagata. La frana in località Val Maso, nel Comune di Valli del Pasubio, è caratterizzata da dinamiche molto diverse rispetto al precedente caso. A seguito delle eccezionali piogge del Novembre 2010, il versante è collassato con un movimento rototraslativo al coronamento, che è evoluto in colata. L’evento si è sviluppato molto rapidamente ed ha coinvolto circa 200'000 m3 di materiale asportato; la superficie di scivolamento si è localizzata a circa 20 m di profondità. Una back analysis della stabilità del versante ha permesso di definire con maggiore accuratezza le proprietà geotecniche dei materiali coinvolti. Poi, i parametri ottenuti sono stati utilizzati per un’analisi disaccopiata di filtrazione e stabilità globale dell’area a monte del coronamento di frana, per valutare l’entità della minima intensità di pioggia in grado di innescare la retrogressione del fenomeno. Ulteriori informazioni sulla frana sono state ricercate tramite l’utilizzo di dati SAR satellitari. A causa della densa vegetazione e degli evidenti cambiamenti morfologici indotti dalla frana, le tecniche PS ed SBAS non sono risultate applicabili. Si è pertanto analizzata l’ampiezza del dato, anziché la fase, utilizzando 9 immagini COSMO-SkyMed, acquisite prima e dopo l’evento. La valutazione dei cambiamenti di ampiezza ha permesso di perimetrare l’area in frana. Infine la tecnica SBAS è stata utilizzata per indagare l’evoluzione dei sinkholes che interessano la costa Giordana del Mar Morto, con particolare attenzione alla porzione sud-orientale della costa, denominata Ghor Al Haditha. Grazie ai numerosi riferimenti bibliografici relativi a quest’area (Bartov et al., 2000; Closson et al., 2007, 2009; Abou Karaki et al., 2005; Abelson et al., 2006; Akawwi et al., 2009; Ezersky et al., 2013) sono chiare le ragioni del verificarsi di questi dissesti e della subsidenza lungo tutta la costa del lago. L’innesco è connesso all’ingente sfruttamento, a scopo civile ed industriale, delle acque del Mar Morto, il cui livello si sta abbassando di circa 1 m/anno. La conseguenza di questo sfruttamento è una sostituzione dell’acqua salina, presente in profondità, con acqua dolce di falda, la quale causa la dissoluzione degli strati salini presenti nel terreno. L’area è stata analizzata utilizzando immagini ERS, Envisat e COSMO-SkyMed. I primi due dataset hanno evidenziato la subsidenza che affligge le coste, senza permettere di isolare gli spostamenti dovuti ai singoli sinkhole, a causa della risoluzione spaziale di 25 m di questi dati SAR. L’utilizzo dei dati COSMO ha invece permesso di identificare gli spostamenti dovuti ai sinkholes in modo molto dettagliato, grazie all’alta risoluzione spaziale di questi dati (3m x 3m) e al breve tempo di rivisitazione del satellite. Uno specifico sinkhole è stato individuato ed analizzato studiandone l’evoluzione temporale. Sulla base dei risultati ottenuti dal processamento SBAS è stato definito un modello analitico: partendo dal campo di spostamenti superficiali sono stati derivati i parametri geometrici della sorgente e stimata la variazione di volume associata al fenomeno. Le esperienze fatte hanno evidenziato come i dati SAR satellitari permettano di ottenere importanti informazioni riguardo le dinamiche dei fenomeni di instabilità. Il grado di dettaglio di tali informazioni dipendono da diversi fattori, quali la risoluzioni spaziale del dato, la numerosità e la vicinanza temporale dei dati analizzati, la presenza di vegetazione più o meno fitta, la velocità degli spostamenti. La possibilità di utilizzare i dati SAR per ottenere informazioni utili alla creazione di un modello numerico è stata testata in diverse condizioni. In presenza di movimenti molto rapidi, che superano il valore massimo di velocità rilevabile, e cambiamenti netti della copertura vegetativa provocano una perdita di coerenza, è possibile analizzare l’ampiezza del segnale anziché la fase. Nel caso della frana in località Val Maso, è stato possibile mappare la superficie soggetta a deformazioni, fornendo un possibile strumento fondamentale per la gestione dell’emergenza post-evento. Nonostante la presenza di vegetazione nel versante in frana, in località Cischele, la tecnica SBAS ha permesso di stimare una componente dello spostamento superficiale, grazie all’attenta calibrazione di alcuni parametri del processamento. La morfologia pianeggiante della costa del Mar Morto, in località Ghor Al Haditha, e la scarsa presenza di vegetazione, hanno permesso di ottenere precise informazioni relativamente alle deformazioni superficiali indotte dal subsidenza e sinkholes, tanto da poter generare un modello analitico del fenomeno, utile alla creazione di un sistema di early warning, sulla base dei movimenti che precedono un possibile evento catastrofico.

Satellite geodesy plays an important role in earth observation. This dissertation presents three applications of satellite geodesy in environmental and climate change. Three satellite geodesy techniques are used: high-precision Global Positioning System (GPS), the Gravity Recovery and Climate Experiment (GRACE) and Interferometric Synthetic Aperture Radar (InSAR). In the first study, I use coastal uplift observed by GPS to study the annual changes in mass loss of the Greenland ice sheet. The data show both spatial and temporal variations of coastal ice mass loss and suggest that a combination of warm atmospheric and oceanic condition drove these variations. In the second study, I use GRACE monthly gravity change estimates to constrain recent freshwater flux from Greenland. The data show that Arctic freshwater flux started to increase rapidly in the mid-late 1990s, coincident with a decrease in the formation of dense Labrador Sea Water, a key component of the deep southward return flow od the Atlantic Meridional Overturning Circulation (AMOC). Recent freshening of the polar oceans may be reducing formation of Labrador Sea Water and hence may be weakening the AMOC. In the third study, I use InSAR to monitor ground deformation caused by CO2 injection at an enhanced oil recovery site in west Texas. Carbon capture and storage can reduce CO2 emitted from power plants, and is a promising way to mitigate anthropogenic warming. From 2007 to 2011, ~24 million tons of CO2 were sequestered in this field, causing up to 10 MPa pressure buildup in a reservoir at depth, and surface uplift up to 10 cm. This study suggests that surface displacement observed by InSAR is a cost-effective way to estimate reservoir pressure change and monitor the fate of injected fluids at waste disposal and CO2 injection sites.

Cette étude illustre les résultats d’une activité expérimentale basée sur des couples d’images ERS et ENVISAT, appliquée en Calabre (Italie du sud) pour la période 1998-2007. L’objectif de ce travail a été la détection de subsidences, de glissements de terrain et de l’évaluation des conditions du risque pour une zone stratégiquement très importante tel que la « Piana di Lamzia » avec l’utilisation de données dérivées de l’interféromètre SAR et leur intégration dans un SIG. Après avoir présenté les principes des techniques utilisées et l’illustration de certaines approches originales dans leur implémentation, on a montré quelques résultats de leurs applications. En particulier nous avons focalisé l’attention sur les zones urbaines et l’environnement des villes de Vibo Valentia et Lamezia Terme et sur le réseau des infrastructures présentes. Le travail a porté sur la standardisation d’une procédure opérationnelle avec l’intégration d’un logiciel expérimental. Les apports de la technique concernent à la fois la localisation, la caractérisation et la quantification des phénomènes affectant la surface topographique. L’ensemble des informations obtenues fournit des indications inédites et précieuses à la compréhension de certains phénomènes et à leur modélisation. Pour ce qui concerne l’apport direct de la technique au contrôle des infrastructures, elle semble résulter adaptée que pour une étude indirecte. Une analyse plus fine ne serait possible qu’avec l’utilisation de la technique des Permanent Scatterers
The work shows the experimental results based on ERS and ENVISAT data, developed in the central area of Calabria since 1998 up to 2007 (Envisat).The objective is to use SAR derived elevation data to improve subsidence prediction, landslides, earth motion and damage assessment for a important regional area such as "Piana of Lamezia". After a synthetic presentation of the technique and the illustration of an original approaches in it implementation, we have showed the thematic results. In particular, we have dealt with the urban areas of Vibo Valentia and Lamezia Terme cities, their surroundings, and the network of infrastructures. Works carried to the standardization of an operational procedure with the integration of experimental software. The contributions of the technique relate at the same time the localization, characterization and quantification of the phenomena affecting topographic surface. The obtained information provides new and important indications to the comprehension of different phenomena and their modelling. Concerning the direct contribution of the DInSAR technique to the control of the infrastructures it seems to still result adapts for a indirect study. Currently, not being completely operative new satellites SAR with metric and sub-metric resolution, a finer analysis would be possible only with the use of the Permanent Scatterers technique

Dynamical mass estimates down to the planet-mass regime can help to understand planet formation. We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of FW Tau C, a proposed similar to 10M(Jup) planet-mass companion at similar to 330 au from the host binary FW Tau AB. We spatially and spectrally resolve the accretion disk of FWTau C in (CO)-C-12 (2-1). By modeling the Keplerian rotation of gas, we derive a dynamical mass of similar to 0.1 M-circle dot. Therefore, FW Tau C is unlikely a planet, but rather a low-mass star with a highly inclined disk. This also suggests that FW Tau is a triple system consisting of three similar to 0.1. M-circle dot stars.

Multi-wavelength observations provide a complementary view of the formation of young, directly imaged planetmass companions. We report the ALMA 1.3 mm and Magellan adaptive optics H alpha, i', z', and YS observations of the GQ Lup system, a classical T Tauri star with a 10-40 M-Jup substellar companion at similar to 110 au projected separation. We estimate the accretion rates for both components from the observed Ha fluxes. In our similar to 0.'' 05 resolution ALMA map, we resolve GQ Lup A's disk in the. dust continuum, but no signal is found from the companion. The disk is compact, with a radius of similar to 22 au, a dust mass of similar to 6M(circle plus), an inclination angle of similar to 56 degrees, and a very flat surface density profile indicative of a radial variation in dust grain sizes. No gaps or inner cavity are found in the disk, so there is unlikely a massive inner companion to scatter GQ Lup B outward. Thus, GQ Lup B might have formed in situ via disk fragmentation or prestellar core collapse. We also show that GQ Lup A's disk is misaligned with its spin axis, and possibly with GQ Lup B's orbit. Our analysis on the tidal truncation radius of GQ Lup A's disk suggests that GQ Lup B's orbit might have a low eccentricity.

La tesi propone un processo di indagine per il rilievo di edifici storici e la generazione di prodotti a valenza metrica, al fine di ottenere una modalità di analisi completa, che si avvale di un’alta precisione di misura, per lo studio geometrico del manufatto d’interesse. I principali obiettivi di questa trattazione sono: la documentazione e caratterizzazione geometrica dell'edificato, tramite rilevamento laser scanning e GNSS; lo studio degli spostamenti al suolo del territorio circostante il sito di indagine, tramite interferometria satellitare; la ricerca e lo studio di eventuali relazioni tra gli spostamenti a scala territoriale e i risultati delle indagini a scala di edificio. Si propone l’integrazione di queste tecniche come strumento per l’analisi strutturale dell’edificio allo stato di fatto e per il monitoraggio delle evoluzioni future della struttura, in rapporto con quelle dell’ambiente circostante. Per testare le potenzialità del processo, lo si applica al Monastero di San Domenico sito in Montecreto, Modena (MO). Ottenuta la restituzione del rilievo laser scanner del Complesso, si vuole mettere in relazione lo spostamento del suolo con il rilievo fotografico del quadro fessurativo acquisito in loco, tramite l’analisi geometrica condotta attraverso il modello elaborato. Il processo d’indagine proposto offre grandi vantaggi: l’alta risoluzione ed accuratezza delle misure effettuate e l’alta densità di dato rilevato creano un continuum spaziale di dati, restituendo una documentazione completa del sito indagato. L'integrazione con altre tecniche topografiche (ad esempio GNSS) permette, di arricchire il prodotto finale e di verificarne la bontà del processo di elaborazione. Sebbene non sia stato possibile identificare una relazione diretta tra dato di spostamento al suolo e quadro fessurativo, il modello elaborato è uno strumento di analisi geometrica che, in confronto con indagini pregresse o future, agevolerà l’identificazione di criticità strutturali.

L’imagerie à très haute dynamique s’applique à de nombreux domaines de recherche en astronomie et astrophysique. Cette problématique observationnelle est abordée sur plusieurs fronts par de nombreuses techniques complémentaires : coronographie, interferométrie, optique adaptative, controle de front d’onde et discrimination des speckles. La combinaison de celles ci permet d’atteindre un haut contraste avec pour ultime objectif l’imagerie d’exoplanètes et l’étude de l’environnement stellaire. Le travail présenté dans ce manuscrit se focalise sur la coronographie et plus particulièrement sur l’optimisation active du procedé d’occultation en fonction du contexte observationnel.La première partie de cette recherche traite de l’observation d’objets résolus par le développement d’un masque focal de Lyot de diamètre variable. La deuxième partie s’applique à étendre le concept du masque focal adaptatif au masque de phase de type Roddier pour l’observation de l’environnement proche d’objets non résolus. L’utilisation des propriétés des cristaux liquides permet de réaliser un déphasage par rotation de polarisation et une modulation de transmission à l’extérieur du masque. Cette modulation permet un controle actif d’optimisation de l’interférence pour une adéquation du masque au contexte observationnel : longueur d’onde, morphologie d’image et défauts intrinsèques au masque, agitation atmosphérique. La dernière partie de ce manuscrit ébauche de nouvelles perspectives quant à la possibilité d’une imagerie à haut contraste. La modulation temporelle de phase transmise par un masque focal adaptatif est mise à profit par l’utilisation des méthodes de détection synchrone
High contrast imaging of extra-solar planets and environments of bright astro- physical objects in general, such as stars, active galactic nuclei or objects of the Solar System is a challenging task. Different approaches are needed if the bright region to occult is optically resolved or not. We present the Adaptive Mask concept, observations on sky and numerical simulations show the usefulness of the proposed methods to optimize the efficiency of the coronagraphs for optically resolved or non resolved objects. Accessing small IWA is considered as an edge as it provides substantial scientific and technical advantages. One of the difficulties of accessing small IWA is that coronagraphs become very sensitive to low-order aberrations such as tip-tilt. Our original approach aims at integrating the small IWA capability and the mitigation of sensitivity to low-order aberrations within the coronagraph itself. Our concept is applicable to both low and high Strehl regimes, corresponding to current and next generation AO systems. The adaptive coronagraph can adapt dynamically, in quasi real time, to adjust to the observing conditions to deliver a stable and optimized contrast at the science image level. The mask adaptability both in size, phase and amplitude also compensates for manufacturing errors of the mask itself, and potentially for chromatic effects. The mask adaptability concept using a local phase modulation in the focal plane allows synchronous modulation for high dynamic range synchronous detection of a faint target immersed in a background. The coherence of the speckles with the central star is used to discriminate them from proper companions

La mia tesi dal titolo ”Applicazione della tecnica PSinSAR™ allo studio di fenomeni franosi lenti: casi di studio in Emilia-Romagna” ha avuto come obiettivo quello di mostrare le potenzialità e i limiti della tecnica PSinSAR nel monitoraggio di fenomeni franosi localizzati in Val Marecchia. Ho svolto, nel capitolo due, un’analisi preliminare dell’area di studio andando a evidenziare prima le caratteristiche climatiche, piogge medie annue e le temperature minime e massime, e a seguire sono passato a descrivere l’inquadramento geologico e geomorfologico. L’area della Val Marecchia è, da questo punto di vista, molto particolare poggiando su quella che è definita dagli autori “coltre della Val Marecchia”; essa è un complesso alloctono sovrascorso ai terreni autoctoni della successione Umbro – Romagnola - Marchigiana. La traslazione verso Est della coltre avvenne per "scatti", in funzione delle principali fasi tettoniche appenniniche, separati da momenti di pausa in cui sedimentarono le formazioni più recenti le quali poi si spostarono in modo solidale con la coltre. La coltre, infatti, è costituita da un insieme di formazioni di età diverse e in particolare ritroviamo, partendo da quella più antica l’unità ligure, l’unità subligure e infine l’unità epiligure. La presenza di formazioni più recenti sopra ad altre più antiche rende unica la morfologia della vallata con enormi blocchi rocciosi poggianti su un substrato in genere argilloso come nell’esempio più famoso della rupe di San Leo. Da queste analisi è emersa un’altra caratteristica peculiare della valle cioè la forte tendenza a essere interessata da dissesti di varie tipologie. Gli indici di franosità mostrano che nella zona alta della vallata circa il 50% del territorio è interessato da dissesti, valore che decresce leggermente nella parte media e bassa della valle. Il motivo di tale instabilità è da imputare in parte alla forte erosione che avviene sulle placche epiliguri e in parte alle caratteristiche scadenti del substrato che è per lo più composto di argille e arenarie. Per quanto riguarda le tipologie di frane in Val Marecchia la situazione è molto eterogenea; in particolari le tre tipologie più frequenti sono il colamento lento, lo scivolamento rotazionale/traslativo e le frane di tipo complesso. Nel terzo capitolo ho descritto la tecnica PSinSAR; essa si basa sull’elaborazione di scene riprese da satellite per giungere alla formazione di una rete di punti, i PS, di cui conosciamo i movimenti nel tempo. I Permanent Scatterer (PS) sono dei bersagli radar individuati sulla superficie terrestre dal sensori satellitari caratterizzati per il fatto di possedere un’elevata stabilità nel tempo alla risposta elettromagnetica. I PS nella maggior parte dei casi corrispondono a manufatti presenti sulla superficie quali edifici, monumenti, strade, antenne e tralicci oppure ad elementi naturali come per esempio rocce esposte o accumuli di detrito. Lo spostamento viene calcolato lungo la linea di vista del satellite, per cui il dato in uscita non mostra lo spostamento effettivo del terreno, ma l'allontanamento o l'avvicinamento del punto rispetto al satellite. La misure sono sempre differenziali, ovvero sono riferite spazialmente a un punto noto a terra chiamato reference point, mentre temporalmente alla data di acquisizione della prima immagine. La tecnica PSinSAR proprio per la sua natura è "cieca" rispetto ai movimenti in direzione Nord-Sud. Le scene utilizzate per la creazione dei dataset di PS derivano quasi interamente dai satelliti ERS e ENVISAT. Tuttora sono disponibili anche le scene dei satelliti TerraSAR-X, RADARSAT e Cosmo Skymed. I sensori utilizzati in questo ambito sono i SAR (Synthetic Aperture Radar) che sono sensori attivi, cioè emettono loro stessi l'energia necessaria per investigare la superficie terrestre al contrario dei sensori ottici. Questo permette di poter acquisire scene anche di notte e in condizioni di cielo nuvoloso. La tecnica PSinSAR presenta molti vantaggi rispetto alle tecniche interferometriche tradizionali essa, infatti, è immune agli errori di decorrelamento temporale e spaziale oltre agli errori atmosferici, che portavano ad avere precisioni non inferiori a qualche cm, mentre ora l’errore di misura sulla velocità media di spostamento si attesta in genere sui 2 mm. La precisione che si ha nella georeferenziazione dei punti è in genere di circa 4-7 m lungo la direzione Est e circa 1-2 m in quella Nord. L’evoluzione di PSinSAR, SqueeSAR, permette un numero maggiore di punti poiché oltre ai Permanent Scatterers PS, tramite un apposito algoritmo, calcola anche i Distribuited Scatterer DS. I dataset di dati PS che ho utilizzato nel mio lavoro di tesi (PSinSAR) derivano, come detto in precedenza, sia da scene riprese dal satellite ERS che da ENVISAT nelle due modalità ascendenti e discendenti; nel primo caso si hanno informazioni sui movimenti avvenuti tra il 1992 e il 2000 mentre per l’ENVISAT tra il 2002 e il 2008. La presenza di dati PS nelle due modalità di ripresa sulla stessa zona permette tramite alcuni calcoli di ricavare la direzione effettiva di spostamento. È importante però sottolineare che, a seconda della modalità di ripresa, alcune aree possono risultare in ombra, per questo nell’analisi dei vari casi di studio non sempre sono stati utilizzabili tutti i dataset. Per l'analisi dei vari casi di studio, presentati nel capitolo 4, ho utilizzato diverso materiale cartografico. In particolare mi sono servito delle Carte Tecniche Regionali (CTR) a scala 1:10000 e 1:5000, in formato digitale, come base cartografica. Sempre in formato digitale ho utilizzato anche le carte geologiche e geomorfologiche dell'area della Val Marecchia (fogli 266, 267, 278) oltre, per finire, agli shapefile presi dal database online del Piano stralcio dell’Assetto Idrogeologico PAI. Il software usato per la realizzazione del lavoro di tesi è stato ArcGIS di proprietà di ESRI. Per ogni caso di studio ho per prima cosa effettuato un'analisi dal punto di vista geologico e geomorfologico, in modo da fare un quadro delle formazioni presenti oltre ad eventuali fenomeni franosi mostrati dalle carte. A seguire ho svolto un confronto fra il dato PS, e quindi i valori di spostamento, e la perimetrazione mostrata nel PAI. Per alcuni casi di studio il dato PS ha mostrato movimenti in aree già perimetrate nel PAI come "in dissesto", mentre in altri il dato satellitare ha permesso di venire a conoscenza di fenomeni non conosciuti (come ad esempio nel caso di Monte Gregorio). Per ogni caso di studio ho inoltre scelto alcuni PS caratteristici (solitamente quelli a coerenza maggiore) e ho ricavato la relativa serie storica. In questo modo è stato possibile verificare lo spostamento durante tutti gli anni in cui sono state prese le scene (dal 1992 al 2000 per dati ERS, dal 2002 al 2008 per dati ENVISAT) potendo quindi mettere in luce accelerazioni o assestamenti dei fenomeni nel tempo, oltre a escludere la presenza di trend di spostamento anomali imputabili nella maggior parte dei casi a errori nel dato. L’obiettivo della tesi è stato da una parte di verificare la bontà del dato PS nell’interpretazione dei movimenti dovuti a dissesti franosi e dall’altra di fare un confronto tra il dato di spostamento ricavato dai PS e i vari inventari o carte di piano. Da questo confronto sono emerse informazioni molti interessanti perché è stato possibile avere conferme di movimento su dissesti già conosciuti (Sant’Agata Feltria, San Leo e altri) ma anche di venire a conoscenza di fenomeni non conosciuti (Monte Gregorio). In conclusione è emerso dal mio lavoro che il monitoraggio tramite tecnica PSinSAR necessita di essere integrato con le tecniche tradizionali poiché presenta alcune limitazioni importanti come l’impossibilità di "vedere" movimenti veloci o lungo la direzione Nord-Sud, oltre ad avere dati in aree vegetate o scarsamente abitate. I vantaggi sono però notevoli potendo monitorare con un’unica ripresa vaste porzioni di territorio oltre ad avere serie storiche consistenti, in grado di evidenziare i movimenti avvenuti nel passato. Tale tecnica quindi, secondo il mio parere, può essere utilizzata come supporto alla stesura di cartografia di fenomeni franosi fornendo informazioni aggiuntive rispetto alle varie tecniche tradizionali come il GPS, sondaggi geotecnici e sondaggi inclinometrici.

Subtle gravitational e ects can be measured by precisely monitoring the position of a test mass. Often this is done by measuring the displacement between two or more test objects. The Gravity Recovery and Climate Experiment (GRACE) satellites do just this, by continuously tracking changes in their separation with micron-level sensitivity. These displacement measurements are used to infer the gravitational potential of the Earth, which has enabled scientists to monitor key aspects of our climate since their launch in 2002. It is planned that the GRACE Follow-On satellites will include a laser ranging instrument as a technology demonstrator to improve the displacement measurement. Before science operation commences and measurements can begin, the laser on each satellite needs to be precisely pointed towards the opposite satellite, and thus the satellites must undergo an initial acquisition scan after launch to establish the laser link. This thesis is concerned with developing technology for the GRACE Follow-On laser ranging instrument and exploring interferometric techniques for future satellite missions. In the following chapters, we experimentally demonstrate an acquisition system with GRACE Follow-On-like parameters, requiring no additional hardware but relying on the photodetectors and signal processing equipment already required for science operation. This strategy was developed with multiple collaborators over several years led by C. Mahrdt at the Albert Einstein Institute. To establish the laser link, ve degrees of freedom must be optimized (pitch and yaw for each beam, and the frequency di erence between the two lasers). Laser steering and frequency scanning patterns are combined with a fast Fourier transform-based peak detection algorithm run on each satellite to nd the signal. We successfully demonstrate both stages (commissioning and reacquisition) of the proposed acquisition strategy. One of the core components needed for the GRACE Follow-On laser ranging instrument is the triple mirror assembly (TMA), a modi ed corner cube that symmetrically routes the laser beam around existing hardware about the satellite's center of mass. A prototype triple mirror assembly was designed and constructed by local and international collaborators, and we present optical tests demonstrating three of the performance requirements of the prototype. The path length stability of a beam traveling through the TMA was measured in a test bed resembling the measurement con guration of the GRACE Follow-On interferometer. The parallelism between the incoming and outgoing beams to/from the TMA is measured to the arc second level. Additional measurements quantify changes in the parallelism as the TMA prototype is heated and cooled. Finally, we give a brief overview of digitally-enhanced interferometry, a developing technique for optical metrology which has signi cant advantages over a conventional heterodyne system and could be employed for future space missions. We present an experimental demonstration of the multiplexing capability of the technique, showing an improved displacement sensitivity between measurement points when information from several sensors is combined to suppress errors due to laser frequency noise. We discuss an option for the technique to be applied to future inter-satellite measurement architectures and examine possible simpli cations to the optical bench layout.

In the last decade satellite remote sensing has become an effective tool for monitoring geo-hazard-induced ground motions, and has been increasingly used by scientific community. Geo-hazards direct and indirect costs are currently rising, causing serious socio-economics and casualty losses. Therefore, creating a priority list turns out to be essential to highlight the most relevant ground deformations and to better focus the risk management practices at regional scale. The Sentinel-1 constellation, thanks to the 6-days repeatability and the free availability of the data, allows to easily update the geo-hazard-induced ground motions, compared to other kind of satellite sensors. In this PhD Thesis, the potentialities and drawbacks of the interferometric technique have been presented and then exploited to define three different procedures, applied in different environment and at different scales, for the use of multi-band PSI products. This thesis work represents the main outcome of a three yearslong activity at the Department of Earth Sciences of the University of Florence, Centre technologic de telecomunicacions de Catalunya research center and TRE-Altamira (Barcelona). The main goal is to test and evaluate the potential and applicability of space-borne SAR data, processed by means of different PSI approaches, as operational tools for the characterization of geohazards in different geological and geomorphological environments. For this work, two Italian test areas at regional scale are been selected: Tuscany and Valle d’Aosta Regions. Furthermore a site at detailed scale was analyzed, the mining area of Saline di Volterra (Tuscany). The main goal of the thesis hinges on illustrating different methodologies that could be merged in one single workflow to detect active moving areas, characterize them in detail and cross-correlate the satellite data with ancillary information, implementing the obtained products and results in the Civil Protection chain and geohazard risk management. The proposed case studies were intended as examples, although referred to different environments and geohazards, for the working approaches to be used from regional to detailed scale. For the Tuscany Region, there were exploited Sentinel-1 images for active moving areas detection at regional scale. A hotspot-like methodology was used, exploiting the temporal repetitiveness of Sentinel-1 data analysed by means of the SqueeSAR algorithm to create deformation maps in three different periods with a 6 months update. Thanks to a filtering approach based on a velocity threshold, it was possible extract a total of 652 deformation clusters, divided in three different periods, to study their spatial and temporal evolution. The final output is a flexible geo-database that contains interferometric parameters, geographical, geomorphological and geological information, a brief evaluation of the possible triggering cause and information about the temporal evolution of the moving areas. For the Valle d’Aosta Region, it was used a clustering analysis applied to a large stack of Sentinel-1 satellite interferometric products that has been derived using the SqueeSAR algorithm. Valle d’Aosta Region is an alpine region characterized by a wide spectrum of mass wasting phenomena. The approach, based on simple GIS tools and indexes, allowed detecting 277 moving areas above the selected velocity threshold. Overall, landslides (complex, rotational, Deep Seated Gravitational Slope Deformation (DSGSD)), rock glacier evolution and detrital-related deformation are responsible for the detected motions. In mountainous areas, where the field data collection is sometimes limited or impossible, the presented approach is intended to create priority areas to be focused for further investigations. In this way, it is possible to increase, with reduced economic and personnel costs, the “landslide knowledge” of all the actors involved within the landslide risk management chain at regional scale. In this context, easily updatable clustering methodologies are very useful tools for MTInSAR data analysts; it is possible to obtain reliable results in a fast way and to compare them with previous results. Well knowing the limitations of the interferometric technique, especially in mountain regions, it is reasonable to rely on clustering approaches in order to derive multi-temporal synoptic views of ground motions over wide areas. For the Saline di Volterra case, it is presented a local scale application of multi-temporal satellite interferometry targeting a solution mining area in southern Tuscany. The surroundings of Saline di Volterra host several brine wells that pump water into a salt level at a depth ranging between 60 and 400 m below surface. The mining activity has a relevant environmental impact in terms of depletion of the water resources and in terms of ground motion, creating several sinkholes which were mapped through multi-temporal analysis of orthophotos. The deformation map, obtained through the analysis of Sentinel-1 images, revealed the presence of several subsidence bowls, sometimes corresponding to sinkholes formed in the recent past. The subsidence bowls have a common deformation pattern, with LOS velocities increasing forward the center of the bowl. The temporal evolution of the measurement points can vary a lot on case-basis. Finally, a correlation between LOS velocities and age of formation of sinkholes have been found. The Sentinel-1 images were processed with an ad hoc processing chain, elaborated in Centre Technologic Telecomunicacions Catalunya research center (Barcelona). With this new procedure, it was possible to detect fast deformation rates that are usually puzzling to solve in mining areas. This detailed scale and target-oriented approach demonstrated its capability to provide useful information in terms of density of measurement points and quality of the time series.

This PhD research aims at exploiting PSI techniques for ground displacement detection and mapping at regional and local scale, and for quantitatively and qualitatively analysis of slow-moving landslide phenomena. The work is mainly based on the combined use of ground motion rates provided by PS radar data with conventional geomorphologic tools such as optical data, geo-thematic and in situ information, and further ground-truth data. -------------------------------------------------------------- Questa tesi di Dottorato mira a sfruttare le tecniche PSI per l’identificazione e la mappatura di spostamenti del terreno a scala regionale e locale, e per l'analisi quantitativa e qualitativa dei fenomeni franosi lenti. Il lavoro si basa sull'uso combinato dei valori di velocità fornite da dati radar PS con strumenti geomorfologici convenzionali quali dati ottici, informazioni geo-tematiche e in situ, dati relativi a verità a terra.

The Qadimah Fault has been mapped as a normal fault running through the middle of a planned $$$50 billion city. For this reason, there is an urgent need to evaluate the seismic hazard that the fault poses to the new development. Although several geophysical studies have supported the existence of a fault, the driving mechanism remains unclear. While a fault controlled by gravity gliding of the overburden on a mobile salt layer is unlikely to be of concern to the city, one caused by the continued extension of a normal rotational fault due to Red Sea rifting could result in a major earthquake. A number of geomorphology and geodetic techniques were used to better understand the fault. An analysis of topographic data revealed a sharp discontinuity in slope aspect and hanging wall tilting which strongly supports the existence of a normal fault. A GPS survey of an emergent reef platform which revealed a tilted coral surface also indicates that deformation has occurred in the region. An interferometric synthetic aperture radar investigation has also been performed to establish whether active deformation is occurring on the fault. Ground movements that could be consistent with inter-seismic strain accumulation have been observed, although the analysis is restricted by the limited data available. However, a simple fault model suggests that the deformation is unlikely due to continued crustal stretching. This, in addition to the lack of footwall uplift in the topography data, suggests that the fault is more likely controlled by a shallow salt layer. However, more work will need to be done in the future to confirm these findings.

Studying recent volcanic and tectonic events in the Red Sea region is important for improving our knowledge of the Red Sea plate boundary and for regional geohazard assessments. However, limited information has been available about the past activity due to insufficient in-situ data and remoteness of some of the activity. In this dissertation, I have used satellite remote sensing to derive new information about several recent volcanic and tectonic events in the Red Sea region. I first report on three volcanic eruptions in the southern Red Sea, the 2007-8 Jebel at Tair eruption and the 2011-12 & 2013 Zubair eruptions, which resulted in formation of two new islands. Series of high- resolution optical images were used to map the extent of lava flows and to observe and analyze the growth and destructive processes of the new islands. I used Interferometric Synthetic Aperture Radar (InSAR) data to study the evolution of lava flows, to estimate their volumes, as well as to generate ground displacements maps, which were used to model the dikes that fed the eruptions. I then report on my work of the 2009 Harrat Lunayyir dike intrusion and the 2004 Tabuk earthquake sequence in western Saudi Arabia. I used InSAR observations and stress calculations to study the intruding dike at Harrat Lunayyir, while I combined InSAR data and Bayesian estimation to study the Tabuk earthquake activity. The key findings of the thesis are: 1) The recent volcanic eruptions in the southern Red Sea indicate that the area is magmatically more active than previously acknowledged and that a rifting episode has been taken place in the southern Red Sea; 2) Stress interactions between an ascending dike intrusion and normal faulting on graben-bounding faults above the dike can inhibit vertical propagation of magma towards the surface; 3) InSAR observations can improve locations of shallow earthquakes and fault model uncertainties are useful to associate earthquake activity with mapped faults; 4). The successful application of satellite remote sensing technologies in studying the recent volcanic and tectonic processes in the Red Sea region implies that remote sensing data are an important resource for the local authorities to monitor geohazards.

The phenomenon of induced seismicity is caused by anthropogenic activity such as: underground and opencast mining, extraction of conventional and unconventional hydrocarbons, construction of water reservoirs and production of geothermal energy. In recent years, interest in induced seismicity increased due to the fact that it causes increasingly stronger earthquakes, even above 4 on the Richter scale. Thus, it poses a threat to people, technical and urban infrastructure. This study analyzed the seismic event of M = 4.6, which occurred on the 15 September 2018 in the Rudna copper mine area in SW Poland. For this purpose, Sentinel 1 satellite data and DInSAR processing method were used to determine the ground movement values in the satellite line of sight. Based on the results for four image pairs, the area disturbed by the seismic event was determined. The maximum values of subsidence ranged from -65 mm to -75 mm depending on the analysed dataset and the area of deformation was determined at approx. 4 km sq. The results indicate the usefulness of the adopted method to determine ground deformation caused by induced seismicity in an underground mining area.