Academic literature on the topic 'Radar sounders'
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Journal articles on the topic "Radar sounders"
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MacGregor, Joseph A., Michael Studinger, Emily Arnold, Carlton J. Leuschen, Fernando Rodríguez-Morales, and John D. Paden. "Brief communication: An empirical relation between center frequency and measured thickness for radar sounding of temperate glaciers." Cryosphere 15, no. 6 (June 7, 2021): 2569–74. http://dx.doi.org/10.5194/tc-15-2569-2021.
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Abstract. Radar sounding of the thickness of temperate glaciers is challenged by substantial volume scattering, surface scattering and high attenuation rates. Lower-frequency radar sounders are often deployed to mitigate these effects, but the lack of a global synthesis of their success limits progress in system and survey design. Here we extend a recent global compilation of glacier thickness measurements (GlaThiDa) with the center frequency for radar-sounding surveys. From a maximum reported thickness of ∼ 1500 m near 1 MHz, the maximum thickness sounded decreases by ∼ 500 m per frequency decade. Between 25–100 MHz, newer airborne radar sounders generally outperform older, ground-based ones. Based on globally modeled glacier thicknesses, we conclude that a multi-element, ≤30 MHz airborne radar sounder could survey most temperate glaciers more efficiently.
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Haynes, Mark S. "Surface and subsurface radar equations for radar sounders." Annals of Glaciology 61, no. 81 (April 2020): 135–42. http://dx.doi.org/10.1017/aog.2020.16.
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AbstractThis work is a collection of radar equations for low-frequency radar sounding and radar in general that emphasize the form of the radar equation for different target and source geometries. This is meant as a handbook for scientists and engineers that work with or analyze radar sounder systems and interpret radar sounding echoes. Lookup tables summarize the results and derivations are provided for each equation.
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Lin, Xin, and Arthur Y. Hou. "Evaluation of Coincident Passive Microwave Rainfall Estimates Using TRMM PR and Ground Measurements as References." Journal of Applied Meteorology and Climatology 47, no. 12 (December 1, 2008): 3170–87. http://dx.doi.org/10.1175/2008jamc1893.1.
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Abstract This study compares instantaneous rainfall estimates provided by the current generation of retrieval algorithms for passive microwave sensors using retrievals from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) and merged surface radar and gauge measurements over the continental United States as references. The goal is to quantitatively assess surface rain retrievals from cross-track scanning microwave humidity sounders relative to those from conically scanning microwave imagers. The passive microwave sensors included in the study are three operational sounders—the Advanced Microwave Sounding Unit-B (AMSU-B) instruments on the NOAA-15, -16, and -17 satellites—and five imagers: the TRMM Microwave Imager (TMI), the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) instrument on the Aqua satellite, and the Special Sensor Microwave Imager (SSM/I) instruments on the Defense Meteorological Satellite Program (DMSP) F-13, -14, and -15 satellites. The comparisons with PR data are based on “coincident” observations, defined as instantaneous retrievals (spatially averaged to 0.25° latitude and 0.25° longitude) within a 10-min interval collected over a 20-month period from January 2005 to August 2006. Statistics of departures of these coincident retrievals from reference measurements as given by the TRMM PR or ground radar and gauges are computed as a function of rain intensity over land and oceans. Results show that over land AMSU-B sounder rain retrievals are comparable in quality to those from conically scanning radiometers for instantaneous rain rates between 1.0 and 10.0 mm h−1. This result holds true for comparisons using either TRMM PR estimates over tropical land areas or merged ground radar/gauge measurements over the continental United States as the reference. Over tropical oceans, the standard deviation errors are comparable between imager and sounder retrievals for rain intensities above 5 mm h−1, below which the imagers are noticeably better than the sounders; systematic biases are small for both imagers and sounders. The results of this study suggest that in planning future satellite missions for global precipitation measurement, cross-track scanning microwave humidity sounders on operational satellites may be used to augment conically scanning microwave radiometers to provide improved temporal sampling over land without degradation in the quality of precipitation estimates.
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Piazzo, L., M. C. Raguso, R. Seu, and M. Mastrogiuseppe. "Signal enhancement for planetary radar sounders." Electronics Letters 55, no. 3 (February 2019): 153–55. http://dx.doi.org/10.1049/el.2018.7284.
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You, Yalei, Veljko Petkovic, Jackson Tan, Rachael Kroodsma, Wesley Berg, Chris Kidd, and Christa Peters-Lidard. "Evaluation of V05 Precipitation Estimates from GPM Constellation Radiometers Using KuPR as the Reference." Journal of Hydrometeorology 21, no. 4 (April 2020): 705–28. http://dx.doi.org/10.1175/jhm-d-19-0144.1.
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AbstractThis study assesses the level-2 precipitation estimates from 10 radiometers relative to Global Precipitation Measurement (GPM) Ku-band precipitation radar (KuPR) in two parts. First, nine sensors—four imagers [Advanced Microwave Scanning Radiometer 2 (AMSR2) and three Special Sensor Microwave Imager/Sounders (SSMISs)] and five sounders [Advanced Technology Microwave Sounder (ATMS) and four Microwave Humidity Sounders (MHSs)]—are evaluated over the 65°S–65°N region. Over ocean, imagers outperform sounders, primarily due to the usage of low-frequency channels. Furthermore, AMSR2 is clearly superior to SSMISs, likely due to the finer footprint size. Over land all sensors perform similarly except the noticeably worse performance from ATMS and SSMIS-F17. Second, we include the Sondeur Atmospherique du Profil d’Humidite Intertropicale par Radiometrie (SAPHIR) into the evaluation process, contrasting it against other sensors in the SAPHIR latitudes (30°S–30°N). SAPHIR has a slightly worse detection capability than other sounders over ocean but comparable detection performance to MHSs over land. The intensity estimates from SAPHIR show a larger normalized root-mean-square-error over both land and ocean, likely because only 183.3-GHz channels are available. Currently, imagers are preferred to sounders when level-2 estimates are incorporated into level-3 products. Our results suggest a sensor-specific priority order. Over ocean, this study indicates a priority order of AMSR2, SSMISs, MHSs and ATMS, and SAPHIR. Over land, SSMIS-F17, ATMS and SAPHIR should be given a lower priority than the other sensors.
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Pettinelli, Elena, Barbara Cosciotti, Sebastian Emanuel Lauro, and Elisabetta Mattei. "An overview of GPR subsurface exploration of planets and moons." Leading Edge 41, no. 10 (October 2022): 672–80. http://dx.doi.org/10.1190/tle41100672.1.
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Geophysical techniques were first tested beyond Earth during the Apollo program. Of those examined, radio-wave propagation methods appeared to be the most suitable for the moon and other solar system bodies. This was due to the electromagnetic characteristics of planetary subsurfaces and the possibility to remotely perform measurements on board spacecrafts and rovers. After the first successful experiment on the moon, more than 20 years passed before ground-penetrating radar (GPR) was included in the payload of a planetary mission. Technological advancements in GPR design and successful results of radio echo sounding measurements for the detection of basal water below terrestrial ice sheets paved the way for the application of similar techniques to search for liquid water in the Martian subsurface. Since deployment of the first two subsurface radar sounders above Mars, the number of proposed planetary missions relying on GPR for surveying the subsurface of planets, moons, and other objects has grown progressively. Six orbiting radar sounders and five GPRs mounted on rovers/landers have been employed so far to explore the moon, Mars, and comet 67P/GC. Some of these are in full operation and some are just starting to operate. Planned missions to the icy moons of Jupiter will also depend heavily on radar sounders to detect evidence of an internal ocean on Europa and to understand the habitability conditions on Europa, Ganymede, and Callisto. Finally, planetary missions to Earth's twin, the planet Venus, could take advantage of GPR to understand the cause of its drastic change in climatic conditions and the geologic phenomena that contributed to changing a watery and hospitable surface into a hot and asphyxiating inhabitable planet.
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Wang, Jianxin, David B. Wolff, Jackson Tan, David A. Marks, Jason L. Pippitt, and George J. Huffman. "Validation of IMERG Oceanic Precipitation over Kwajalein." Remote Sensing 14, no. 15 (August 5, 2022): 3753. http://dx.doi.org/10.3390/rs14153753.
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The integrated Multi-satellitE Retrievals for GPM (IMERG) Version V05B and V06B precipitation products from the Global Precipitation Measurement (GPM) mission are validated against ground-based observations from the Kwajalein Polarimetric S-band Weather Radar (KPOL) deployed at Kwajalein Atoll in the central Pacific Ocean. Such a validation is particularly important as comprehensive surface measurements over the oceans are practically infeasible, which hampers the identification of possible errors, and improvement of future versions of IMERG and other satellite-based retrieval algorithms. The V05B and V06B IMERG products are validated at their native 0.1°, 30 min resolution from 2014 to 2018 based on both volumetric and categorical metrics. This validation study indicates that precipitation rates from both IMERG V05B and V06B are underestimated with respect to radar surface estimates, but the underestimation is much reduced from V05B to V06B. IMERG V06B outperforms V05B with reduced systematic bias and improved precipitation detectability. The IMERG performance is further traced back to its individual sensors and morphing-based algorithms. The overall underestimation in V05B is mainly driven by the negative relative biases from morphing-based algorithms which are largely corrected in V06B. Imagers perform generally better than sounders because of the usage of low-frequency channels in imagers which can better detect emission signals by the hydrometeors. Among imagers, the GPM Microwave Imager (GMI) and Advanced Microwave Scanning Radiometer Version 2 (AMSR2) are the best, followed by Special Sensor Microwave Imager/Sounder (SSMIS). Among sounders, the Microwave Humidity Sounder (MHS) is the best, followed by Advanced Technology Microwave Sounder (ATMS) and the Sounder for Atmospheric Profiling of Humidity in the Intertropics by Radiometry (SAPHIR) for V06B. Among all categories, morph-only and IR + morph only perform better than SAPHIR. SAPHIR shows the worst performance among all categories, likely due to its limited channel selection. It is envisaged that these results will improve our understanding of IMERG performance over oceans and aid in the improvement of future versions of IMERG.
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Bekaert, David, Nicolas Gebert, Chung-Chi Lin, Florence Hélière, Jørgen Dall, Anders Kusk, and Steen Savstrup Kristensen. "Multichannel surface clutter suppression: East Antarctica P-band SAR ice sounding in the presence of grating lobes." Annals of Glaciology 55, no. 67 (2014): 9–21. http://dx.doi.org/10.3189/2014aog67a100.
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AbstractIce sounding with radar is a well-established technique for the retrieval of ice depth, and provides information on ice structures and layering. Airborne radar ice sounders suffer from off-nadir surface clutter that masks the signal from bedrock and ice layers with unwanted but simultaneously received surface reflections. This is of importance for future satellite ice-sounding missions, as the spaceborne geometry leads to strong surface clutter even for deep subsurface returns. This paper presents analysis and comparison of different clutter-suppression techniques applied to data acquired with the European Space Agency's P-band POLarimetric Airborne Radar Ice Sounder (POLARIS). The 4 m long antenna of POLARIS enables simultaneous reception of up to four across-track channels. It was operated in 2011 over Antarctica at a high flight altitude of 3200 m. Different coherent weighting techniques of the receive channels were used to suppress the surface ‘clutter’. However, with a channel spacing of 1.4 times the wavelength, the grating lobe imposes a limitation to the off-nadir angular range in which clutter can be effectively attenuated. Results of ice sounding over Jutulstraumen glacier are described, where we demonstrate a clutter suppression of up to 10 dB.
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Kelly, Kathryn A., and D. Randolph Watts. "Monitoring Gulf Stream Transport by Radar Altimeter and Inverted Echo Sounders." Journal of Physical Oceanography 24, no. 5 (May 1994): 1080–84. http://dx.doi.org/10.1175/1520-0485(1994)024<1080:mgstbr>2.0.co;2.
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Blagoveshchensky, D. V., M. Lester, V. A. Kornienko, I. I. Shagimuratov, A. J. Stocker, and E. M. Warrington. "Observations by the CUTLASS radar, HF Doppler, oblique ionospheric sounding, and TEC from GPS during a magnetic storm." Annales Geophysicae 23, no. 5 (July 28, 2005): 1697–709. http://dx.doi.org/10.5194/angeo-23-1697-2005.
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Abstract. Multi-diagnostic observations, covering a significant area of northwest Europe, were made during the magnetic storm interval (28–29 April 2001) that occurred during the High Rate SolarMax IGS/GPS-campaign. HF radio observations were made with vertical sounders (St. Petersburg and Sodankyla), oblique incidence sounders (OIS), on paths from Murmansk to St. Petersburg, 1050 km, and Inskip to Leicester, 170 km, Doppler sounders, on paths from Cyprus to St. Petersburg, 2800 km, and Murmansk to St. Petersburg, and a coherent scatter radar (CUTLASS, Hankasalmi, Finland). These, together with total electron content (TEC) measurements made at GPS stations from the Euref network in northwest Europe, are presented in this paper. A broad comparison of radio propagation data with ionospheric data at high and mid latitudes, under quiet and disturbed conditions, was undertaken. This analysis, together with a geophysical interpretation, allow us to better understand the nature of the ionospheric processes which occur during geomagnetic storms. The peculiarity of the storm was that it comprised of three individual substorms, the first of which appears to have been triggered by a compression of the magnetosphere. Besides the storm effects, we have also studied substorm effects in the observations separately, providing an improved understanding of the storm/substorm relationship. The main results of the investigations are the following. A narrow trough is formed some 10h after the storm onset in the TEC which is most likely a result of enhanced ionospheric convection. An enhancement in TEC some 2–3 h after the storm onset is most likely a result of heating and upwelling of the auroral ionosphere caused by enhanced currents. The so-called main effect on ionospheric propagation was observed at mid-latitudes during the first two substorms, but only during the first substorm at high latitudes. Ionospheric irregularities observed by CUTLASS were clearly related to the gradient in TEC associated with the trough. The oblique sounder and Doppler observations also demonstrate differences between the mid-latitude and high-latitude paths during this particular storm. Keywords. Ionosphere (Ionospheric disturbances) – Magnetospheric physics (Storms and substorms) – Radio science (Ionospheric propagation)
Dissertations / Theses on the topic "Radar sounders"
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Leonardo, Carrer. "Advanced Signal Processing Methods for Planetary Radar Sounders Data." Doctoral thesis, Università degli studi di Trento, 2018. https://hdl.handle.net/11572/368977.
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Radar sounders are spaceborne electromagnetic sensors specifically designed for subsurface investigations. They operate in the HF/VHF part of the electromagnetic spectrum and are widely employed for applications such as monitoring changes to the polar ice sheets of the Earth and for the study of planetary bodies (e.g. Mars) from satellite. Radar sounding of planetary bodies is a relatively young discipline both in terms of system design and data processing architectures. As a result of the current state of the art in system design, the data recorded by radar sounders are typically affected by artifacts, such as off-nadir surface clutter, which hinders its interpretation by scientists. On top of that, the analysis of the very large of amount of data produced by such systems is typically performed manually by experts thus inherently subjective and time-consuming. Therefore the development of automatic high-level processing strategies for reliable, objective and fast extraction of information is needed.
Accordingly, this thesis work deals with different aspects of radar sounding namely system design, low-level and high-level processing.
The thesis provides three main novel contributions to the state of the art. First, we present a study on system design, performance assessment and 3D electromagnetic simulations of a radar sounding system specifically tailored for detecting lava tubes under the Moon surface. Lava tubes are considered to be important and useful structures. By having a stable temperature and by providing protection against cosmic ray radiation and micrometeorites impacts, they could potentially serve as natural shelter for human outposts on the Moon.
The results presented in this thesis show that a multi-frequency radar sounder is the best option for effectively sound most of the lava tube dimension expected from the literature and that they show unique electromagnetic signature which can be used for their detection.
The second novel contribution is focused on low-level processing and consists in a bio-inspired clutter detection model based on bats echolocation. Very relevant analogies occur between a bat and radar sounder such as the nadir acquisition geometry. The mathematical model proposed in this thesis adapts the bats frequency diversity strategy (i.e. multi-frequency approach) to solve clutter ambiguities to the radar sounding case.
The proposed bio-inspired clutter detection model has been tested and validated on experimental data acquired over Mars. The experimental results showed that the method is able to discriminate in a precise way the radar echoes arising from subsurface targets with respect to off-nadir surface clutter ones.
The third novel contribution of this thesis goes in the direction of high-level processing and in particular of automatic data analysis for accurate and fast extraction of relevant information from radar sounding data. To this extent, we propose a novel automatic method for retrieving the spatial position and radiometric properties of the subsurface layers based on Hidden Markov Models for radar response modeling and the Viterbi Algorithm for the inference step. Furthermore, a novel radargram enhancement and denoising technique has been developed to support the detection step. The effectiveness of the technique has been demonstrated on different radargrams acquired over the North Pole of Mars pointing out its superiority with respect to current state of the art techniques.
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Gerekos, Christopher. "Advanced Backscattering Simulation Methods for the Design of Spaceborne Radar Sounders." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/261416.
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Spaceborne radar sounders are an important class of remote sensing instruments which operate by recording backscattered electromagnetic waves in the vicinity of a solid planetary body. The incoming waves are generally transmitted by the radar itself (active sounding), although external signals of opportunity can also be used (passive sounding). There are currently two major planetary radar sounders under development, both headed to the Jovian icy moons (Europa, Ganymede and Callisto). Designing a radar sounder is a very challenging process involving careful leveraging of heritage and predictive tools, and in which backscattering simulators play a central role. This is especially true for coherent simulators, due to their higher accuracy and the possibility they offer to apply advanced processing techniques on the resulting simulated data, such as synthetic aperture radar focusing, or any other operation which requires field amplitude, phase and polarisation. For this reason, designing computationally-efficient coherent simulators is an important and active research area. The first contribution of this thesis is a novel multilayer coherent simulator based on the Stratton-Chu equation and the linear phase approximation, which can generate realistic simulated radar data on a wide range of surface and subsurface digital elevation models (DEM), using only a fraction of the computational resources that a finite-difference time-domain method would need. Thorough validation was conducted against both theoretical formulations and real data, which confirmed the accuracy of the method. The method was then generalised to noisy active and passive sounding, which is an important capability in the context of the proposed use of passive sounding on the Jovian icy moons. Provided that representative information about the surface and this external field exists, the simulator could compare the relative scientific value of active and passive sounding of a given target under given conditions. However, quality DEMs of the Jovian icy moons are scarce. For this reason we also present a comparative study of the fractal roughness of Europa and Mars (a much better studied body), where we derive fractal analogue maps of twelve types of Europan terrains on Mars. These maps could be used to guide the choice of Martian DEMs on which to perform representative backscattering simulations for future radar missions on Europa. Finally, we explore the possibility of entirely new radar architectures with the novel concept of the distributed radar. In a distributed sounder, very large across-track antennas can be synthesised from smallsats flying on selected orbits, providing a way to obtain a highly-directive antenna without the need to deploy large and complex structures in space. We develop an analytical formulation to treat the problem of beamforming with an array affected by perturbations on the positions of its array elements, and propose a set of Keplerian parameters that enable the concept.
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Gerekos, Christopher. "Advanced Backscattering Simulation Methods for the Design of Spaceborne Radar Sounders." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/261416.
Full textAbstract:
Spaceborne radar sounders are an important class of remote sensing instruments which operate by recording backscattered electromagnetic waves in the vicinity of a solid planetary body. The incoming waves are generally transmitted by the radar itself (active sounding), although external signals of opportunity can also be used (passive sounding). There are currently two major planetary radar sounders under development, both headed to the Jovian icy moons (Europa, Ganymede and Callisto). Designing a radar sounder is a very challenging process involving careful leveraging of heritage and predictive tools, and in which backscattering simulators play a central role. This is especially true for coherent simulators, due to their higher accuracy and the possibility they offer to apply advanced processing techniques on the resulting simulated data, such as synthetic aperture radar focusing, or any other operation which requires field amplitude, phase and polarisation. For this reason, designing computationally-efficient coherent simulators is an important and active research area. The first contribution of this thesis is a novel multilayer coherent simulator based on the Stratton-Chu equation and the linear phase approximation, which can generate realistic simulated radar data on a wide range of surface and subsurface digital elevation models (DEM), using only a fraction of the computational resources that a finite-difference time-domain method would need. Thorough validation was conducted against both theoretical formulations and real data, which confirmed the accuracy of the method. The method was then generalised to noisy active and passive sounding, which is an important capability in the context of the proposed use of passive sounding on the Jovian icy moons. Provided that representative information about the surface and this external field exists, the simulator could compare the relative scientific value of active and passive sounding of a given target under given conditions. However, quality DEMs of the Jovian icy moons are scarce. For this reason we also present a comparative study of the fractal roughness of Europa and Mars (a much better studied body), where we derive fractal analogue maps of twelve types of Europan terrains on Mars. These maps could be used to guide the choice of Martian DEMs on which to perform representative backscattering simulations for future radar missions on Europa. Finally, we explore the possibility of entirely new radar architectures with the novel concept of the distributed radar. In a distributed sounder, very large across-track antennas can be synthesised from smallsats flying on selected orbits, providing a way to obtain a highly-directive antenna without the need to deploy large and complex structures in space. We develop an analytical formulation to treat the problem of beamforming with an array affected by perturbations on the positions of its array elements, and propose a set of Keplerian parameters that enable the concept.
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Sbalchiero, Elisa. "Advanced Methods for Generating and Processing Simulated Radar Sounder Data for Planetary Missions." Doctoral thesis, Università degli studi di Trento, 2022. https://hdl.handle.net/11572/355183.
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Radar sounders (RS) are active instruments that have proved to be able to profile the subsurface of planetary bodies. The design of RS instruments, as well as the interpretation of the acquired data, is a non-trivial task due to the complexity of the scenario of acquisition and the limited amount of information on the targets (especially in planetary exploration). In this context, data simulations are necessary to support the design of the radar, the development of the related processing chain, and the definition of algorithms for the automatic analysis of data.
However, state-of-the-art RS simulation methods are characterized by different trade-offs between simulation accuracy and computational costs. On the one hand, numerical methods, such as the Finite-Difference Time-Domain (FDTD) technique, allow to accurately model the wave-target interaction by exactly solving Maxwell's equations at the cost of very high computational requirements. On the other hand, optical methods, such as the ray-tracing based Multi-layer Coherent Simulator (MCS), rely on approximated solution of Maxwell's equations that allow for a better usage of computational resources at the cost of a less accurate modeling.
Moreover, simulators produce raw or range-compressed only data, making it difficult to interpret and analyze them via direct comparison with the real data, which are typically processed also for azimuth compression.
In this thesis, we present four main contributions related to the simulation of RS data to address the above-mentioned limitations.
The first and second contributions thus present 3D simulations of selected targets of two new RS instruments, i.e., the Radar for Icy Moon Exploration (RIME) and the EnVision Subsurface Radar Sounder (SRS). The simulations are performed with the FDTD and MCS simulators.
Despite producing good results in terms of detection probability of the selected targets, these two contributions highlight the above-mentioned gaps in the literature of simulation of RS data. The first main limitation is the lack of methods that can accurately model both large and small-scale scattering phenomena at relatively low computational costs. This problem is addressed by the third contribution of this thesis, which presents a novel integrated simulation technique that models both large and small-scale surface scattering phenomena by combining the advantages of the FDTD and MCS techniques, in an accurate and computationally efficient way. The second problem identified is the lack of SAR processing techniques to be applied to the simulated radargrams. This is addressed in the fourth contribution which presents a range-Doppler method for focusing raw radar sounder data simulated with 3D coherent electromagnetic simulators. The method is general and can be applied to any electromagnetic simulator, and is demonstrated for both the FDTD and MCS methods. The results presented throughout the thesis indicate that the proposed methods advance the state-of-the-art of techniques for both generating and processing simulated RS data.
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Ferro, Adamo. "Advanced Methods for the Analysis of Radar Sounder and VHR SAR Signals." Doctoral thesis, Università degli studi di Trento, 2011. https://hdl.handle.net/11572/368915.
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In the last decade the interest in radar systems for the exploration of planetary bodies and for Earth Observation (EO) from orbit increased considerably. In this context, the main goal of this thesis is to present novel methods for the automatic analysis of planetary radar sounder (RS) signals and very high resolution (VHR) synthetic aperture radar (SAR) images acquired on the Earth. Both planetary RSs and VHR SAR systems are instruments based on relatively recent technology which make it possible to acquire from
orbit new types of data that before were available only in limited areas from airborne acquisitions. The use of orbiting platforms allows the acquisition of a huge amount of data on large areas. This calls for the development of effective and automatic methods for the extraction of information tuned on the characteristics of these new systems. The work has been organized in two parts.
The first part is focused on the automatic analysis of data acquired by planetary RSs. RS signals are currently mostly analyzed by means of manual investigations and the topic
of automatic analysis of such data has been only marginally addressed in the literature. In this thesis we provide three main novel contributions to the state of the art on this topic. First, we present a theoretical and empirical statistical study of the properties of RS signals. Such a study drives the development of two novel automatic methods for the generation of subsurface feature maps and for the detection of basal returns. The second contribution is a method for the extraction of subsurface layering in icy environments, which is capable to detect linear features with sub-pixel accuracy. Moreover, measures for the analysis of the properties of the detected layers are proposed. Finally, the third contribution is a technique for the detection of surface clutter returns in radargrams.
The proposed method is based on the automatic matching between real and clutter data generated according to a simulator developed in this thesis.
The second part of this dissertation is devoted to the analysis of VHR SAR images, with special focus on urban areas. New VHR SAR sensors allow the analysis of such areas
at building level from space. This is a relatively recent topic, which is especially relevant for crisis management and damage assessment. In this context, we describe in detail an empirical and theoretical study carried out on the relation between the double-bounce effect of buildings and their orientation angle. Then, a novel approach to the automatic detection and reconstruction of building radar footprints from VHR SAR images is pre-sented. Unlike most of the methods presented in the literature, the developed method can extract and reconstruct building radar footprints from single VHR SAR images. The technique is based on the detection and combination of primitive features in the image, and introduces the concept of semantic meaning of the primitives.
Qualitative and quantitative experimental results obtained on real planetary RS and spaceborne VHR SAR data confirm the effectiveness of the proposed methods.
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Thakur, Sanchari. "Advanced Methods for Simulation and Performance Analysis of Planetary Radar Sounder Data." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/259173.
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Radar sounders (RS) are low frequency remote sensing instruments that profile the shallow subsurface of planetary bodies providing valuable scientific information. The prediction of the RS performance and the interpretation of the target properties from the RS data are challenging due to the complex electromagnetic interaction between many acquisition variables. RS simulations address this issue by forward modeling this complex interaction and simulating the radar response. However, existing simulators require detailed and subjective modeling of the target in order to produce realistic radargrams. For less-explored planetary bodies, such information is difficult to obtain with high accuracy. Moreover, the high computational requirements of conventional electromagnetic simulators prohibit the simulation of a large number of radargrams. Thus, it is not possible to generate and analyze a database of simulated radargrams representative of the acquisition scenario that would be very useful for both the RS design and the data analysis phase. To overcome these difficulties and to produce realistic simulated radargrams, this thesis proposes two novel approaches to the simulation and analysis of the radar response. The first contribution is a simulation approach that leverages the data available over geological analogs of the investigated target and reprocesses them to obtain the simulated radargrams. The second contribution is a systematic approach to the generation and analysis of a database of simulated radargrams representing the possible scenarios during the RS acquisition. The database is analyzed to predict the RS performance, to design the instrument parameters, and to support the development of automatic target detection algorithms. To demonstrate the proposed techniques the thesis addresses their use in two future RS instruments, which are at different phases of development: (1) the Radar for Icy Moons Exploration (RIME) and (2) a RS for Earth observation of the polar ice caps. The first contribution focuses on the analysis of the detectability of complex tectonic targets on the icy moons of Jupiter by RIME by simulating the radar response of 3D target models. The second contribution presents a feasibility study for an Earth orbiting RS based on the proposed simulation approaches.
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Thakur, Sanchari. "Advanced Methods for Simulation and Performance Analysis of Planetary Radar Sounder Data." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/259173.
Full textAbstract:
Radar sounders (RS) are low frequency remote sensing instruments that profile the shallow subsurface of planetary bodies providing valuable scientific information. The prediction of the RS performance and the interpretation of the target properties from the RS data are challenging due to the complex electromagnetic interaction between many acquisition variables. RS simulations address this issue by forward modeling this complex interaction and simulating the radar response. However, existing simulators require detailed and subjective modeling of the target in order to produce realistic radargrams. For less-explored planetary bodies, such information is difficult to obtain with high accuracy. Moreover, the high computational requirements of conventional electromagnetic simulators prohibit the simulation of a large number of radargrams. Thus, it is not possible to generate and analyze a database of simulated radargrams representative of the acquisition scenario that would be very useful for both the RS design and the data analysis phase. To overcome these difficulties and to produce realistic simulated radargrams, this thesis proposes two novel approaches to the simulation and analysis of the radar response. The first contribution is a simulation approach that leverages the data available over geological analogs of the investigated target and reprocesses them to obtain the simulated radargrams. The second contribution is a systematic approach to the generation and analysis of a database of simulated radargrams representing the possible scenarios during the RS acquisition. The database is analyzed to predict the RS performance, to design the instrument parameters, and to support the development of automatic target detection algorithms. To demonstrate the proposed techniques the thesis addresses their use in two future RS instruments, which are at different phases of development: (1) the Radar for Icy Moons Exploration (RIME) and (2) a RS for Earth observation of the polar ice caps. The first contribution focuses on the analysis of the detectability of complex tectonic targets on the icy moons of Jupiter by RIME by simulating the radar response of 3D target models. The second contribution presents a feasibility study for an Earth orbiting RS based on the proposed simulation approaches.
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Donini, Elena. "Advanced methods for simulation-based performance assessment and analysis of radar sounder data." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/304147.
Full textAbstract:
Radar Sounders (RSs) are active sensors that transmit in the nadir electromagnetic (EM) waves with a low frequency in the range of High-Frequency and Very-High-Frequency and relatively wide bandwidth. Such a signal penetrates the surface and propagates in the subsurface, interacting with dielectric interfaces. This interaction yields to backscattered echoes detectable by the antenna that are coherently summed and stored in radargrams. RSs are used for planetary exploration and Earth observation for their value in investigating subsurface geological structures and processes, which reveal the past geomorphological history and possible future evolution. RS instruments have several parameter configurations that have to be designed to achieve the mission science goals. On Mars, radargram visual analyses revealed the icy layered deposits and liquid water evidence in the poles. On the Earth, RSs showed relevant structures and processes in the cryosphere and the arid areas that help to monitor the subsurface geological evolution, which is critical for climate change. Despite the valuable results, visual analysis is subjective and not feasible for processing a large amount of data. Therefore, a need emerges for automatic methods extracting fast and reliable information from radargrams. The thesis addresses two main open issues of the radar-sounding literature: i) assessing target detectability in simulated orbiting radargrams to guide the design of RS instruments, and ii) designing automatic methods for information extraction from RS data. The RS design is based on assessing the performance of a given instrument parameter configuration in achieving the mission science goals and detecting critical targets. The assessment guides the parameter selection by determining the appropriate trade-off between the achievable performance and technical limitations. We propose assessing the detectability of subsurface targets (e.g., englacial layering and basal interface) from satellite radar sounders with novel performance metrics. This performance assessment strategy can be applied to guide the design of the SNR budget at the surface, which can further support the selection of the main EORS instrument parameters. The second contribution is designing automatic methods for analyzing radargrams based on fuzzy logic and deep learning. The first method aims at identifying buried cavities, such as lava tubes, exploiting their geometric and EM models. A fuzzy system is built on the model that detects candidate reflections from the surface and the lava tube boundary. The second and third proposed methods are based on deep learning, as they showed groundbreaking results in several applications. We contributed with an automatic technique for analyzing radargram acquired in icy areas to investigate the basal layer. To this end, radargrams are segmented with a deep learning network into literature classes, including englacial layers, bedrock, and echo-free zone (EFZ) and thermal noise, as well as new classes of basal ice and signal perturbation. The third method proposes an unsupervised segmentation of radargrams with deep learning for detecting subsurface features. Qualitative and quantitative experimental results obtained on planetary and terrestrial radargrams confirm the effectiveness of the proposed methods, which investigate new subsurface targets and allow an improvement in terms of accuracy when compared to other state-of-the-art methods.
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Donini, Elena. "Advanced methods for simulation-based performance assessment and analysis of radar sounder data." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/304147.
Full textAbstract:
Radar Sounders (RSs) are active sensors that transmit in the nadir electromagnetic (EM) waves with a low frequency in the range of High-Frequency and Very-High-Frequency and relatively wide bandwidth. Such a signal penetrates the surface and propagates in the subsurface, interacting with dielectric interfaces. This interaction yields to backscattered echoes detectable by the antenna that are coherently summed and stored in radargrams. RSs are used for planetary exploration and Earth observation for their value in investigating subsurface geological structures and processes, which reveal the past geomorphological history and possible future evolution. RS instruments have several parameter configurations that have to be designed to achieve the mission science goals. On Mars, radargram visual analyses revealed the icy layered deposits and liquid water evidence in the poles. On the Earth, RSs showed relevant structures and processes in the cryosphere and the arid areas that help to monitor the subsurface geological evolution, which is critical for climate change. Despite the valuable results, visual analysis is subjective and not feasible for processing a large amount of data. Therefore, a need emerges for automatic methods extracting fast and reliable information from radargrams. The thesis addresses two main open issues of the radar-sounding literature: i) assessing target detectability in simulated orbiting radargrams to guide the design of RS instruments, and ii) designing automatic methods for information extraction from RS data. The RS design is based on assessing the performance of a given instrument parameter configuration in achieving the mission science goals and detecting critical targets. The assessment guides the parameter selection by determining the appropriate trade-off between the achievable performance and technical limitations. We propose assessing the detectability of subsurface targets (e.g., englacial layering and basal interface) from satellite radar sounders with novel performance metrics. This performance assessment strategy can be applied to guide the design of the SNR budget at the surface, which can further support the selection of the main EORS instrument parameters. The second contribution is designing automatic methods for analyzing radargrams based on fuzzy logic and deep learning. The first method aims at identifying buried cavities, such as lava tubes, exploiting their geometric and EM models. A fuzzy system is built on the model that detects candidate reflections from the surface and the lava tube boundary. The second and third proposed methods are based on deep learning, as they showed groundbreaking results in several applications. We contributed with an automatic technique for analyzing radargram acquired in icy areas to investigate the basal layer. To this end, radargrams are segmented with a deep learning network into literature classes, including englacial layers, bedrock, and echo-free zone (EFZ) and thermal noise, as well as new classes of basal ice and signal perturbation. The third method proposes an unsupervised segmentation of radargrams with deep learning for detecting subsurface features. Qualitative and quantitative experimental results obtained on planetary and terrestrial radargrams confirm the effectiveness of the proposed methods, which investigate new subsurface targets and allow an improvement in terms of accuracy when compared to other state-of-the-art methods.
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Ilisei, Ana-Maria. "Advanced Methods for the Analysis of Radar Sounder Data Acquired at the Ice Sheets." Doctoral thesis, Università degli studi di Trento, 2016. https://hdl.handle.net/11572/367890.
Full textAbstract:
The World Climate Research Programme (WCRP) has recently reconfirmed the importance of a better understanding of the Cryosphere for advancing the analysis, modeling and prediction of climate change and its impact on the environment and society. One of the most complete collection of information about the ice sheets and glaciated areas is contained in the data (radargrams) acquired by Radar Sounder (RS) instruments. The need to better understand the structure of the ice sheets and the availability of enourmous quantities of radargrams call for the development of automatic techniques for an efficient extraction of information from RS data. This topic has been only marginally addressed in the literature. Thus, in this thesis we address this challenge by contributing with four novel automatic techniques for the analysis of radargrams acquired at the ice sheets.
The first contribution of this thesis presents a system for the automatic classification of ice subsurface targets in RS data. The core of the system is represented by the extraction of a set of features for target discrimination. The features are based on both the specific statistical properties of the RS signal and the spatial distribution of the ice subsurface targets. The second contribution is an unsupervised model-based technique for the automatic detection and property estimation of ice subsurface targets. This is done by using the parameters of the RS system combined with the output of an automatic image segmentation algorithm. The third contribution presents an automatic technique for the local 3D reconstruction of the ice sheet. It is based on the use of RS and altimeter (ALT) data, and relies on the use of a geostatistical interpolation method and on several statistical measures for validating the interpolation results and the quality of interpolation. The fourth contribution presents a technique for the automatic estimation of radar power losses in ice as a continuous non-linear function of depth, by using RS and ice core data. The technique relies on the detection of ice layers in the RS data, the computation of their reflectivity from the ice core data and the use of the radar equation for loss estimation. Qualitative and quantitative experimental results obtained on real RS data confirm the effectiveness of the first three techniques. Also, preliminary results have been obtained by applying the fourth technique to real RS and ice core data acquired in Greenland.
Due to their advantages over the traditional manual approach, e.g., efficiency, objectivity, possibility of jointly analyzing multisensor data (e.g., RS, ALT), the proposed methods can support the scientific community to enhance the data usage for a better modeling and understanding of the ice sheets. Moreover, they will become even more important in the near future, since the volume of data is expected to grow from the increase in airborne and possible Earth Observation spaceborne RS missions.
Books on the topic "Radar sounders"
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United States. National Aeronautics and Space Administration., ed. Airborne/space-based Doppler lidar wind sounders sampling the PBL and other regions of significant □and U inhomogeneities: Final report under NASA NAS8-40191, covering the period April 1994-March 1998. [Washington, DC: National Aeronautics and Space Administration, 1998.
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United States. National Aeronautics and Space Administration., ed. Airborne/space-based Doppler lidar wind sounders sampling the PBL and other regions of significant Ý and U inhomogeneities: Final report under NASA NAS8-40191, covering the period April 1994-March 1998. [Washington, DC: National Aeronautics and Space Administration, 1998.
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United States. National Aeronautics and Space Administration., ed. Airborne/space-based Doppler lidar wind sounders sampling the PBL and other regions of significant Ý and U inhomogeneities: Final report under NASA NAS8-40191, covering the period April 1994-March 1998. [Washington, DC: National Aeronautics and Space Administration, 1998.
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United States. National Aeronautics and Space Administration. LASA: Lidar Atmospheric Sounder and Altimeter. [Washington]: NASA, 1987.
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George C. Marshall Space Flight Center., ed. RAWS, the spaceborne radar wind sounder: Annual progress report, 1991. Lawrence, Kan: Radar Systems and Remote Sensing Laboratory, University of Kansas Center for Research, Inc., 1991.
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Airborne/space-based Doppler lidar wind sounders sampling the PBL and other regions of significant Ý and U inhomogeneities: Final report under NASA NAS8-40191, covering the period April 1994-March 1998. [Washington, DC: National Aeronautics and Space Administration, 1998.
Find full textBook chapters on the topic "Radar sounders"
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Ono, T., A. Kumamoto, Y. Kasahara, Y. Yamaguchi, A. Yamaji, T. Kobayashi, S. Oshigami, et al. "The Lunar Radar Sounder (LRS) Onboard the Kaguya (SELENE) Spacecraft." In The Kaguya Mission to the Moon, 145–92. New York, NY: Springer New York, 2010. http://dx.doi.org/10.1007/978-1-4419-8122-6_7.
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Howard, Penny McCall. "From ‘where am I?’ to ‘where is that?’ Rethinking navigation." In Environment, Labour and Capitalism at Sea. Manchester University Press, 2017. http://dx.doi.org/10.7228/manchester/9781784994143.003.0005.
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Chapter Four continues the discussion of techniques and technologies with a focus on orientation and navigation. The chapter draws on Tim Ingold’s and James Gibson’s descriptions of orientation as a process of movement through the landscape to find affordances. The chapter describes the techniques used locally for finding position from the 1960s onwards: dead-reckoning, and the use of radar, depth sounders, Decca, and GPS. Challenging anthropological accounts of ‘Western’ navigation that assume Westerners always rely on charts and instruments and that these alienate people from direct relations with their environment, the GPS chartplotter shows the perpetual importance of the subjective and experiential aspects of orientation in a digital age. The chapter argues that alienation is instead produced by relations of ownership and exploitation, and that the chartplotter facilitates the centralisation of fishing knowledge with the skipper and the employment of low-waged migrant workers as crew. While authors such as Edwin Hutchins describe navigation as answering the absolute question ‘where am I?’, the chapter proposes that the aim of navigation is usually to answer the relational question ‘where is that?’
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Clarke, John Hughes. "Present-Day Methods of Depth Measurement." In Continental Shelf Limits. Oxford University Press, 2000. http://dx.doi.org/10.1093/oso/9780195117820.003.0015.
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Bathymetric data are needed to derive the morphological criteria that define the extent of the juridical continental shelf. Two features in particular, the '"foot of slope" and the 2500-m contour, must be defined. The previous chapter considered historical methods of determining bathymetry. This chapter will cover the present day methods that can be used to better meet the need for accurate bathymetry. In order to satisfy the demands of UNCLOS, bathymetric data are required in depths ranging from about 200 m to more than 5000 m. Shallower depths, while useful for demonstrating the morphology of the physical continental shelf, do not bear any relevance to the delineation of juridical continental shelf boundaries, other than where they are required to establish the baseline. Alternate methods to derive bathymetry other than using sound are available. Those involving airborne electromagnetic methods (e.g., electromagnetic induction, red-green lasers, and inversion of sea surface radar images) are not capable of determining depths much in excess of 40 m. The only other method potentially useful for deriving deeper water bathymetry is through inversion of sea surface altimetry obtained from satellites. This will be discussed at the end of this chapter. The optimal method thus remains acoustic. The traditional approach has been to use single-beam echo sounders (see previous chapter). This chapter discusses the more modern '"swath" sonar techniques, which are becoming widely used. The great majority of historic bathymetry has been collected using the single-beam sounding approach. As discussed in chapter 9, this method has a number of limitations, three of the most critical of which are i. incomplete coverage; ii. uncertainty about the exact location of the first arrival of the acoustic pulse; and iii. distortion of short-wavelength topography. In order to achieve more complete coverage, better echo location, and higher spatial resolution, methods were devised to project acoustic energy both within narrower solid angles (figure 10.1) and while deriving this information over angular sectors extending further out from the side of the survey vessel. All the methods commonly applied involved scanning the seabed orthogonal to the ship heading. Sequential scans, accumulated as the ship progresses, form a corridor (or swath) of seabed information (figure 10.2).
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Liou, K. N., and Y. Gu. "Radiative Transfer in Cirrus Clouds: Light Scatting and Spectral Information." In Cirrus. Oxford University Press, 2002. http://dx.doi.org/10.1093/oso/9780195130720.003.0017.
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The importance of cirrus clouds in climate has been recognized in the light of a number of intensive composite field observations: the First ISCCP Regional Experiment (FIRE) I in October-November 1986; FIRE II in November-December 1991; the European experiment on cirrus (ICE/EUCREX) in 1989; Subsonic Aircraft: Contrail and Cloud Effect Special Study (SUCCESS) in April 1996. Based on observations from the ground-based lidar and radar, airborne instrumentation, and satellites, cirrus clouds are typically located in the upper troposphere and lower stratosphere (Liou 1986). The formation, maintenance, and dissipation of cirrus clouds are directly associated with synoptic and mesoscale disturbances as well as related to deep cumulus outflows. Increases of high cloud cover have been reported at a number of urban airports in the United States based on surface observations spanning 40 years (Liou et al. 1990; Frankel et al. 1997). These increases have been attributed to the contrails and water vapor produced by jet airplane traffic. Satellite observations from NOAA polar-orbiting High-Resolution Infrared Radiation Sounder (HIRS) using the CO2 slicing method (Wylie et al. 1994) also show that cirrus cloud cover substantially increased between 60° S and 60° N during a 4-year period from June 1989 to September 1993. Understanding the role of cirrus clouds in climate must begin with reliable modeling of their radiative properties for incorporation in climate models as well as determination of the global variability of their composition, structure, and optical properties. Development of the remote sensing methodologies for the detection and retrieval of the ubiquitous visible and subvisual cirrus clouds requires the basic scattering, absorption, and polarization data for ice crystals in conjunction with appropriate radiative transfer models. We present the fundamentals involving radiative transfer in cirrus clouds and review pertinent research. In section 13.1, an overview of the subject of light scattering by ice crystals is presented in which we discuss a unification of the geometric optics approach for large ice particles and the finite-difference time domain numerical solution for small ice particles, referred to as the unified theory. Section 13.2 presents radiative transfer in cirrus clouds involving two unique properties: orientation of nonspherical ice crystals and cloud inhomogeneity.
Conference papers on the topic "Radar sounders"
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Moore, Theresa, and John Paden. "Array Manifold Calibration for Multichannel Radar ICE Sounders." In IGARSS 2020 - 2020 IEEE International Geoscience and Remote Sensing Symposium. IEEE, 2020. http://dx.doi.org/10.1109/igarss39084.2020.9323719.
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Raguso, Maria Carmela, Lorenzo Piazzo, Marco Mastrogiuseppe, Roberto Seu, and Roberto Orosei. "Resolution Enhancement and Interference Suppression for Planetary Radar Sounders." In 2018 26th European Signal Processing Conference (EUSIPCO). IEEE, 2018. http://dx.doi.org/10.23919/eusipco.2018.8553468.
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Carrer, Leonardo, Renato Croci, and Lorenzo Bruzzone. "A robust on-board tracking technique for spaceborne radar sounders." In IGARSS 2015 - 2015 IEEE International Geoscience and Remote Sensing Symposium. IEEE, 2015. http://dx.doi.org/10.1109/igarss.2015.7325953.
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Wood, S. A., G. D. Emmitt, D. Bai, L. S. Wood, and S. Greco. "A Coherent Lidar Simulation Model for Simulating Space-Based and Aircraft-Based Lidar Winds." In Coherent Laser Radar. Washington, D.C.: Optica Publishing Group, 1995. http://dx.doi.org/10.1364/clr.1995.me11.
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The U.S. Air Force (USAF) seeks reliable measurements of winds in the vicinity of clouds from the perspective of a satellite platform or high altitude aircraft. These wind observations may be used as input to tactical decision aids or assimulated into weather forecast models. There is also interest in making direct wind measurements below clouds by sampling through optically thin gaps. To develop an optimal design concept for such lidar platforms, a simulation model has been developed to address questions of optimum laser wavelength, pulse length, minimum power, scanning strategies, optimal signal processing and wind computation algorithms. This paper presents an operational simulation model (Defense Lidar Simulation Model (DLSM)) for space-based/airborne coherent Doppler lidar wind sounders that produce simulated lidar winds using either global or mesoscale atmospheric model wind fields.
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Carrer, Leonardo, Sanchari Thakur, and Lorenzo Bruzzone. "Clutter Discrimination by Estimation of Direction of Arrival in Spaceborne Distributed Radar Sounders." In IGARSS 2022 - 2022 IEEE International Geoscience and Remote Sensing Symposium. IEEE, 2022. http://dx.doi.org/10.1109/igarss46834.2022.9883901.
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Frearson, Nick, and Tej Dhakal. "Design and Performance of the Icepod LC-130 Deep and Shallow Radar Sounders." In IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium. IEEE, 2018. http://dx.doi.org/10.1109/igarss.2018.8519125.
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Ferro, Adamo, Alain Pascal, and Lorenzo Bruzzone. "A novel method for automatic clutter detection in radargrams acquired by orbiting radar sounders." In IGARSS 2012 - 2012 IEEE International Geoscience and Remote Sensing Symposium. IEEE, 2012. http://dx.doi.org/10.1109/igarss.2012.6350741.
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Gossard, Earl E., J. E. Gaynor, and Robert Zamora. "Finestructure of Elevated Inversions: Implications for Optical Systems." In Optical Remote Sensing. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/ors.1985.tuc5.
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An experiment is described that combines in situ measurements made with very fast response sensors on a 300 m tower at the Boulder (Colorado) Atmospheric Observatory (Kaimal and Gaynor, 1983), with remote sensing of atmospheric layer structure by acoustic and FM-CW radar sounders (e.g., Little, 1969; Richter, 1969). A finestructure of laminae is often present within elevated inversion layers that is reminiscent of the sheet and layer structure found in the ocean thermocline and in lakes and estuaries (e.g., Gregg, 1982). Figure 1 shows an acoustic record of such a stepped profile event through which a moving carriage on the tower carried temperature, humidity and wind sensors along time-height trajectories shown by the superimposed staight lines. The temperature measurements were made with platinum wires, humidity was measured with a Lyman-α humidiometer, and wind was measured by three-component sonic anemometers. The_data were then digitized at_a 10 Hz rate, and the carriage rose at 0.56 ms-1 and descended at 0.58 ms-1. Figure 2 shows the resulting profiles of temperature, humidity and wind. The transition through the sheets and layers within the inversion is often extremely abrupt with very large gradients. Near_the center of the lower sheet the local gradient of temperature was 6°C m-1. An experiment is described that combines in situ measurements made with very fast response sensors on a 300 m tower at the Boulder (Colorado) Atmospheric Observatory (Kaimal and Gaynor, 1983), with remote sensing of atmospheric layer structure by acoustic and FM-CW radar sounders (e.g., Little, 1969; Richter, 1969). A finestructure of laminae is often present within elevated inversion layers that is reminiscent of the sheet and layer structure found in the ocean thermocline and in lakes and estuaries (e.g., Gregg, 1982). Figure 1 shows an acoustic record of such a stepped profile event through which a moving carriage on the tower carried temperature, humidity and wind sensors along time-height trajectories shown by the superimposed staight lines. The temperature measurements were made with platinum wires, humidity was measured with a Lyman-α humidiometer, and wind was measured by three-component sonic anemometers. The_data were then digitized at_a 10 Hz rate, and the carriage rose at 0.56 ms-1 and descended at 0.58 ms-1. Figure 2 shows the resulting profiles of temperature, humidity and wind. The transition through the sheets and layers within the inversion is often extremely abrupt with very large gradients. Near_the center of the lower sheet the local gradient of temperature was 6°C m-1.
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Jara, Victor A., Kevin M. Player, Deebu Abi, Fernando Rodriguez-Morales, Sivaprasad Gogineni, Ayyangar R. Harish, and Carl Leuschen. "Portable temperate ice depth sounder radar (TIDSoR)." In 2008 IEEE Radar Conference (RADAR). IEEE, 2008. http://dx.doi.org/10.1109/radar.2008.4720906.
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Curran, R., J. Bilbro, and D. Fitzjarrald. "The Laser Atmospheric Wind Sounder (LAWS)." In Coherent Laser Radar. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/clr.1987.thc3.
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