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Bordbari, R., Y. Maghsoudi i M. Salehi. "BUILT-UP AREA DETECTION BASED ON SUBSPACE PROJECTIONS USING POLARIMETRIC SAR DATA". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-4/W4 (26.09.2017): 37–41. http://dx.doi.org/10.5194/isprs-archives-xlii-4-w4-37-2017.
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The task of detecting and identifying objects remotely has long been an area of intense interest and active research. Active sensing of objects with radio waves is a whole new domain of target detection which is made available by radar remote sensors. Land cover/use information extraction is one of the most important applications of radar remote sensing, especially in urban areas. In this paper, we take a new look at the built-up area extraction problem in polarimetric SAR (PolSAR) data and assume canonical scattering mechanisms as our signal sources which combination of them with appropriate weight fractions formed a scattering vector of each pixel. The set of the scattering mechanisms is divided into two groups: the scattering mechanism of built-up area, and non-objected scattering mechanisms. Then, we describe a technique which simultaneously annihilates the effect of non-objected scattering mechanisms, and detects the presence of a scattering mechanism of interest. The experimental results on several quad-polarimetric datasets show the significant agreement with expected results, while saving computational complexity.
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Sergievskaya, Irina, Stanislav Ermakov, Alexey Ermoshkin, Ivan Kapustin, Alexander Molkov, Olga Danilicheva i Olga Shomina. "Modulation of Dual-Polarized X-Band Radar Backscatter Due to Long Wind Waves". Remote Sensing 11, nr 4 (19.02.2019): 423. http://dx.doi.org/10.3390/rs11040423.
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Investigation of microwave scattering mechanisms is extremely important for developing methods for ocean remote sensing. Recent studies have shown that a common two-scale scattering model accounting for resonance (Bragg) scattering has some drawbacks, in particular it often overestimates the vertical-to-horizontal polarization radar return ratio and underestimates the radar Doppler shifts if the latter are assumed as associated with quasi linear resonance surface waves. It is supposed nowadays that radar backscattering at moderate incidence angles is determined not only by resonance Bragg mechanism but also contains non polarized (non Bragg) component which is associated supposedly with wave breaking but which is still insufficiently studied. Better understanding of the scattering mechanisms can be achieved when studying variations of radar return due to long wind waves. In this paper, results of experiments from an Oceanographic Platform on the Black Sea using dual co-polarized X-band scatterometers working at moderate incidence are presented and variations of Bragg and non-Bragg components (BC and NBC, respectively) and radar Doppler shifts are analysed. It is established that BC and NBC are non-uniformly distributed over profile of dominant (decametre-scale) wind waves (DWW). Variations of BC are characterized by some “background” return weakly modulated with the dominant wind wave periods, while NBC is determined mostly by rare and strong spikes occurred near the crests of the most intense individual waves in groups of DWW. We hypothesize that the spikes are due to intensification of nonlinear structures on the profile of short, decimetre-scale wind waves when the latter are amplified by intense DWW. Bragg scattering in slicks under the experimental conditions was suppressed stronger than NBC and spikes dominated in total radar return. It is obtained that radar Doppler shifts at HH-polarization are larger than at VV-polarization, particularly in slicks, the same relation is for NBC and BC Doppler shifts, thus indicating different scattering mechanisms for these components.
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Sui, Ran, Junjie Wang, Dejun Feng i Yong Xu. "Full-polarization radar target feature modulation based on active polarization conversion metasurface". Journal of Applied Physics 132, nr 17 (7.11.2022): 174903. http://dx.doi.org/10.1063/5.0107643.
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Electromagnetic (EM) metasurfaces comprising artificially designed subwavelength unit cells have drawn considerable attention due to the EM properties beyond the limits of natural materials. As one of the representative structures, active polarization conversion metasurface (APCM) is switchable by loading active components. It provides great freedom to manipulate the polarization state of EM waves. However, the current research mainly focused on the application of communication and paid less attention to the radar effect of APCM. APCM redistributes electromagnetic wave energy in multi-polarization channels, so it will have great application potential in polarimetric radar. Herein, based on the fully polarimetric radar one-dimensional high resolution range profile, the radar effect of time-modulated metasurface is studied. For this purpose, a method of target scattering mechanisms manipulation and a polarization-insensitive structure of APCM are proposed. The amplitude-phase joint modulation method is specifically analyzed in detail. The distance transformation and virtual multi-target phenomena are further discovered. Virtual targets along the distance dimension are generated in multi-polarization channels, while the scattering mechanisms of k-order targets are effectively manipulated. The relationship between the target scattering matrix and the modulation parameters is obtained. It may provide an effective method for the application of active metasurface in fully polarimetric radars.
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Sergievskaya, Irina A., Stanislav A. Ermakov, Aleksey V. Ermoshkin, Ivan A. Kapustin, Olga V. Shomina i Alexander V. Kupaev. "The Role of Micro Breaking of Small-Scale Wind Waves in Radar Backscattering from Sea Surface". Remote Sensing 12, nr 24 (19.12.2020): 4159. http://dx.doi.org/10.3390/rs12244159.
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The study of the microwave scattering mechanisms of the sea surface is extremely important for the development of radar sensing methods. Some time ago, Bragg (resonance) scattering of electromagnetic waves from the sea surface was proposed as the main mechanism of radar backscattering at moderate incidence angles of microwaves. However, it has been recently confirmed that Bragg scattering is often unable to correctly explain observational data and that some other physical mechanisms should be taken into consideration. The newly introduced additional scattering mechanism was characterized as non-polarized, or non-Bragg scattering, from quasi-specular facets appearing due to breaking wave crests, the latter usually occurring in moderate and strong winds. In this paper, it was determined experimentally that such non-polarized radar backscattering appeared not only for rough sea conditions in which wave crests strongly break and “white caps” occur, but also at very low wind velocities close to their threshold values for the wave generation process. The experiments were performed using two polarized Doppler radars. The experiments demonstrated that a polarization ratio, which characterizes relative contributions of non-polarized and Bragg components to the total backscatter, changed slightly with wind velocity and wind direction. Detailed analysis of radar Doppler shifts revealed two types of scatterers responsible for the non-polarized component. One type of scatterer, moving with the velocities of decimeter-scale wind waves, determined radar backscattering at low winds. We identified these scatterers as “microbreakers” and related them to nonlinear features in the profile of decimeter-scale waves, like bulges, toes and parasitic capillary ripples. The scatterers of the second type were associated with strong breaking, moved with the phase velocities of meter-scale breaking waves and appeared at moderate winds additionally to the “microbreakers”. Along with strong breakers, the impact of microbreaking in non-polarized backscattering at moderate winds remained significant; specifically the microbreakers were found to be responsible for about half of the non-polarized component of the radar return. The presence of surfactant films on the sea surface led to a significant suppression of the small-scale non-Bragg scattering and practically did not change the non-Bragg scatterer speed. This effect was explained by the fact that the nonlinear structures associated with dm-scale waves were strongly reduced in the presence of a film due to the cascade mechanism, even if the reduction of the amplitude of dm waves was weak. At the same time, the velocities of non-Bragg scatterers remained practically the same as in non-slick areas since the phase velocity of dm waves was not affected by the film.
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Tonboe, R. T., L. T. Pedersen i C. Haas. "Simulation of the satellite radar altimeter sea ice thickness retrieval uncertainty". Cryosphere Discussions 3, nr 2 (21.07.2009): 513–59. http://dx.doi.org/10.5194/tcd-3-513-2009.
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Abstract. Although it is well known that radar waves penetrate into snow and sea ice, the exact mechanisms for radar-altimeter scattering and its link to the depth of the effective scattering surface from sea ice are still unknown. Previously proposed mechanisms linked the snow ice interface, i.e. the dominating scattering horizon, directly with the depth of the effective scattering surface. However, simulations using a multilayer radar scattering model show that the effective scattering surface is affected by snow-cover and ice properties. With the coming Cryosat-2 (planned launch 2009) satellite radar altimeter it is proposed that sea ice thickness can be derived by measuring its freeboard. In this study we evaluate the radar altimeter sea ice thickness retrieval uncertainty in terms of floe buoyancy, radar penetration and ice type distribution using both a scattering model and ''Archimedes' principle''. The effect of the snow cover on the floe buoyancy and the radar penetration and on the ice cover spatial and temporal variability is assessed from field campaign measurements in the Arctic and Antarctic. In addition to these well known uncertainties we use high resolution RADARSAT SAR data to simulate errors due to the variability of the effective scattering surface as a result of the sub-footprint spatial backscatter and elevation distribution sometimes called preferential sampling. In particular in areas where ridges represent a significant part of the ice volume (e.g. the Lincoln Sea) the simulated altimeter thickness estimate is lower than the real average footprint thickness. This means that the errors are large, yet manageable if the relevant quantities are known a priori. A discussion of the radar altimeter ice thickness retrieval uncertainties concludes the paper.
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Batool, Sidra, Fabrizio Frezza, Fabio Mangini i Patrizio Simeoni. "Introduction to Radar Scattering Application in Remote Sensing and Diagnostics: Review". Atmosphere 11, nr 5 (18.05.2020): 517. http://dx.doi.org/10.3390/atmos11050517.
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The manuscript reviews the current literature on scattering applications of RADAR (Radio Detecting And Ranging) in remote sensing and diagnostics. This paper gives prime features for a variety of RADAR applications ranging from forest and climate monitoring to weather forecast, sea status, planetary information, and mapping of natural disasters such as the ones caused by earthquakes. Both the fundamental parameters involved in scattering mechanisms of RADAR applications and the factors affecting RADAR performances are also discussed.
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SHARIFF, KARIM, i ALAN WRAY. "Analysis of the radar reflectivity of aircraft vortex wakes". Journal of Fluid Mechanics 463 (25.07.2002): 121–61. http://dx.doi.org/10.1017/s0022112002008674.
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Radar has been proposed as a way of tracking wake vortices to reduce aircraft spacing and tests have revealed radar echoes from aircraft wakes in clear air. The mechanism causing refractive index gradients in these tests is thought to be the same as that for homogeneous and isotropic atmospheric turbulence in the Kolmogorov inertial range, for which there is a scattering analysis due to Tatarski. In reality, however, the structure of aircraft wakes has a significant coherent part superimposed with turbulence, about whose structure very little is known. This work adopts a picture of a coherent (in fact two-dimensional) wake to perform a scattering analysis and calculate the reflected power. In particular, two simple mechanisms causing refractive index gradients are considered: (A) radial pressure (and therefore density) gradient in a columnar vortex arising from the rotational flow; (B) adiabatic transport of atmospheric fluid within a descending oval surrounding a vortex pair. In the scattering analysis, Tatarski's weak scattering approximation is kept but the usual assumptions of a far field and a uniform incident wave are dropped. Neither assumption is generally valid for a wake that is coherent across the radar beam. For analytical insight, an approximate analysis that invokes, in addition to weak scattering, the far-field and wide cylindrical beam assumptions, is also developed and compared with the more general analysis. Reflectivities calculated for the oval (mechanism B) are within 2–13 dB m2 of the measurements (≈−70 dB m2) of MIT Lincoln Laboratory at Kwajalein atoll. However, the present predictions have a cut-off away from normal incidence which is not present in the measurements. This implies that the two-dimensional picture is not entirely complete. Estimates suggest that the thin layer of vorticity which is baroclinically generated at the boundary of the oval is turbulent and this may account for reflectivity away from normal incidence. The reflectivity of a vortex (mechanism A) is comparable to that of the oval (mechanism B) but occurs at a frequency (about 50 MHz) that is lower than those considered in all the experiments to date. This result may be useful because: (i) existing atmospheric radars (known as ST radars) already operate at this frequency and so the present prediction could be verified; (ii) rain clutter is not a problem at this frequency; (iii) mechanism A is more robust because it is independent of atmospheric stratification.
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Arii, Motofumi, Hiroyoshi Yamada, Shoichiro Kojima i Masato Ohki. "Review of the Comprehensive SAR Approach to Identify Scattering Mechanisms of Radar Backscatter from Vegetated Terrain". Electronics 8, nr 10 (29.09.2019): 1098. http://dx.doi.org/10.3390/electronics8101098.
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In a field of polarimetric synthetic aperture radar (SAR) remote sensing, various kinds of polarimetric decomposition techniques have been proposed. However, poor validations prevent them from operational applications. A true composition ratio of scattering mechanisms within a radar backscatter plays a key role. To overcome the issue, a novel comprehensive SAR approach to accurately identify a contribution of each scattering mechanism has been introduced. This is based on multiparametric SAR observation combined with a numerical model simulation. In this article, a comprehensive SAR approach is concisely reviewed to accelerate the research in this field. First, popular model-based polarimetric decompositions are introduced and their limitations are shown. Then, a behavior of scattering mechanisms is analyzed by the discrete scatterer model with some results using real multiparametric SAR data. A comprehensive SAR approach must be essential to realize an operational use of polarimetric SAR data.
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Mittal, Vikas, Dharmendra Singh i Lalit Mohan Saini. "Critical analysis of classification techniques for polarimetric synthetic aperture radar data". International Journal of Advances in Intelligent Informatics 2, nr 1 (16.04.2016): 7. http://dx.doi.org/10.26555/ijain.v2i1.52.
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Full polarimetry SAR data known as PolSAR contains information in terms of microwave energy backscattered through different scattering mechanisms (surface-, double- and volume-scattering) by the targets on the surface of land. These scattering mechanisms information is different in different features. Similarly, different classifiers have different capabilities as far as identification of the targets corresponding to these scattering mechanisms. Extraction of different features and the role of classifier are important for the purpose of identifying which feature is the most suitable with which classifier for land cover classification. Selection of suitable features and their combinations have always been an active area of research for the development of advanced classification algorithms. Fully polarimetric data has its own advantages because its different channels give special scattering feature for various land cover. Therefore, first hand statistics HH, HV and VV of PolSAR data along with their ratios and linear combinations should be investigated for exploring their importance vis-à-vis relevant classifier for land management at the global scale. It has been observed that individually first hand statistics yield low accuracies. And their ratios are also not improving the results either. However, improved accuracies are achieved when these natural features are stacked together.
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Bondur, V. G., T. N. Chimitdorzhiev, A. V. Dmitriev, P. N. Dagurov, A. I. Zakharov i L. N. Zakharova. "Using radar polarimetry to monitor changes in backscattering mechanisms in landslide zones for the case study of the Bureya river bank collapse". Исследования Земли из Космоса, nr 4 (17.08.2019): 3–17. http://dx.doi.org/10.31857/s0205-9614201943-17.
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The possibilities of radar polarimetry methods for identification of landslide zones are analyzed here. The fact of transformation of the dominant scattering type by the reflecting surface was used as a key feature of the landslide zone. ALOS-2 PALSAR-2 polarimetric data were processed using the Freeman–Durden and Cloude–Pottier decompositions for the four test sites selected in the area of a landslide caused by the Bureya river bank collapse. The decomposition results are consistent with each other in general, however, some areas show significant differences due to the specifics of the basic model provisions. It is shown that before the landslide event on the landslide area there were three main mechanisms of radar signal scattering: surface, volume, and double scattering. After the collapse, this area is characterized by a single scattering from the surface with large-scale irregularities and without vegetation. So, the landslide area can be confidently recognized. The considerable potential of using the radar polarimetry method for remote diagnostics of the effects of landslide phenomena has been demonstrated.
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Chang, Ling, Anurag Kulshrestha, Bin Zhang i Xu Zhang. "Extraction and Analysis of Radar Scatterer Attributes for PAZ SAR by Combining Time Series InSAR, PolSAR, and Land Use Measurements". Remote Sensing 15, nr 6 (13.03.2023): 1571. http://dx.doi.org/10.3390/rs15061571.
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Extracting meaningful attributes of radar scatterers from SAR images, PAZ in our case, facilitates a better understanding of SAR data and physical interpretation of deformation processes. The attribute categories and attribute extraction method are not yet thoroughly investigated. Therefore, this study recognizes three attribute categories: geometric, physical, and land-use attributes, and aims to design a new scheme to extract these attributes of every coherent radar scatterer. Specifically, we propose to obtain geometric information and its dynamics over time of the radar scatterers using time series InSAR (interferometric SAR) techniques, with SAR images in HH and VV separately. As all InSAR observations are relative in time and space, we convert the radar scatterers in HH and VV to a common reference system by applying a spatial reference alignment method. Regarding the physical attributes of the radar scatterers, we first employ a Random Forest classification method to categorize scatterers in terms of scattering mechanisms (including surface, low-, high-volume, and double bounce scattering), and then assign the scattering mechanism to every radar scatterer. We propose using a land-use product (i.e., TOP10NL data for our case) to create reliable labeled samples for training and validation. In addition, the radar scatterers can inherit land-use attributes from the TOP10NL data. We demonstrate this new scheme with 30 Spanish PAZ SAR images in HH and VV acquired between 2019 and 2021, covering an area in the province of Friesland, the Netherlands, and analyze the extracted attributes for data and deformation interpretation.
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Sassen, Kenneth, James R. Campbell, Jiang Zhu, Pavlos Kollias, Matthew Shupe i Christopher Williams. "Lidar and Triple-Wavelength Doppler Radar Measurements of the Melting Layer: A Revised Model for Dark- and Brightband Phenomena". Journal of Applied Meteorology 44, nr 3 (1.03.2005): 301–12. http://dx.doi.org/10.1175/jam-2197.1.
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Abstract During the recent Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE) field campaign in southern Florida, rain showers were probed by a 0.523-μm lidar and three (0.32-, 0.86-, and 10.6-cm wavelength) Doppler radars. The full repertoire of backscattering phenomena was observed in the melting region, that is, the various lidar and radar dark and bright bands. In contrast to the ubiquitous 10.6-cm (S band) radar bright band, only intermittent evidence is found at 0.86 cm (K band), and no clear examples of the radar bright band are seen at 0.32 cm (W band), because of the dominance of non-Rayleigh scattering effects. Analysis also reveals that the relatively inconspicuous W-band radar dark band is due to non-Rayleigh effects in large water-coated snowflakes that are high in the melting layer. The lidar dark band exclusively involves mixed-phase particles and is centered where the shrinking snowflakes collapse into raindrops—the point at which spherical particle backscattering mechanisms first come into prominence during snowflake melting. The traditional (S band) radar brightband peak occurs low in the melting region, just above the lidar dark-band minimum. This position is close to where the W-band reflectivities and Doppler velocities reach their plateaus but is well above the height at which the S-band Doppler velocities stop increasing. Thus, the classic radar bright band is dominated by Rayleigh dielectric scattering effects in the few largest melting snowflakes.
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Tonboe, Rasmus T., Vishnu Nandan, John Yackel, Stefan Kern, Leif Toudal Pedersen i Julienne Stroeve. "Simulated Ka- and Ku-band radar altimeter height and freeboard estimation on snow-covered Arctic sea ice". Cryosphere 15, nr 4 (13.04.2021): 1811–22. http://dx.doi.org/10.5194/tc-15-1811-2021.
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Abstract. Owing to differing and complex snow geophysical properties, radar waves of different wavelengths undergo variable penetration through snow-covered sea ice. However, the mechanisms influencing radar altimeter backscatter from snow-covered sea ice, especially at Ka- and Ku-band frequencies, and the impact on the Ka- and Ku-band radar scattering horizon or the “track point” (i.e. the scattering layer depth detected by the radar re-tracker) are not well understood. In this study, we evaluate the Ka- and Ku-band radar scattering horizon with respect to radar penetration and ice floe buoyancy using a first-order scattering model and the Archimedes principle. The scattering model is forced with snow depth data from the European Space Agency (ESA) climate change initiative (CCI) round-robin data package, in which NASA's Operation IceBridge (OIB) data and climatology are included, and detailed snow geophysical property profiles from the Canadian Arctic. Our simulations demonstrate that the Ka- and Ku-band track point difference is a function of snow depth; however, the simulated track point difference is much smaller than what is reported in the literature from the Ku-band CryoSat-2 and Ka-band SARAL/AltiKa satellite radar altimeter observations. We argue that this discrepancy in the Ka- and Ku-band track point differences is sensitive to ice type and snow depth and its associated geophysical properties. Snow salinity is first increasing the Ka- and Ku-band track point difference when the snow is thin and then decreasing the difference when the snow is thick (>0.1 m). A relationship between the Ku-band radar scattering horizon and snow depth is found. This relationship has implications for (1) the use of snow climatology in the conversion of radar freeboard into sea ice thickness and (2) the impact of variability in measured snow depth on the derived ice thickness. For both (1) and (2), the impact of using a snow climatology versus the actual snow depth is relatively small on the radar freeboard, only raising the radar freeboard by 0.03 times the climatological snow depth plus 0.03 times the real snow depth. The radar freeboard is a function of both radar scattering and floe buoyancy. This study serves to enhance our understanding of microwave interactions towards improved accuracy of snow depth and sea ice thickness retrievals via the combination of the currently operational and ESA's forthcoming Ka- and Ku-band dual-frequency CRISTAL radar altimeter missions.
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Staples, Gordon, i Ridha Touzi. "The Application of RADARSAT-2 Quad-Polarized Data for Oil Slick Characterization". International Oil Spill Conference Proceedings 2014, nr 1 (1.05.2014): 2242–52. http://dx.doi.org/10.7901/2169-3358-2014.1.2242.
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ABSTRACT Spaceborne radar data has been extensively used to monitor numerous oil spills worldwide. The radar imagery provides information on the spatial extent of the oil, but in general, there is limited information on the characteristics of the oil such as the discrimination of sheen from emulsion. The full polarimetry capabilities of RADARSAT-2 were investigated in this study using acquisitions collected over the Gulf of Mexico. In this study, the Cloude-Pottier target decomposition algorithm was used to extract polarimetric information from RADARSAT-2 quad-polarized images acquired over the Macondo oil spill in the Gulf of Mexico. The Cloude-Pottier entropy (H) provides a measure of the amount of mixing between scattering mechanisms. For a wind-roughened ocean surface, the scattering is dominated by a single dominant scattering mechanism, namely Bragg scattering (H → 0). In the presence of an oil slick, however, the entropy increases (H → 1) which is due to the number independent scattering mechanisms increasing due to damping of the small-scale Bragg waves. Comparison of entropy with the over flight observations indicated that the variability of the entropy was consistent with the variability of the oil properties suggesting that the entropy was providing a qualitative measure of the oil characteristics. Specifically, when there was open water and a thin sheen, the entropy was close to 0, but in the presence thicker oil due to the presence of, for example, an emulsion, the entropy had values that were close to 1.
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Davison, Jennifer L., Robert M. Rauber i Larry Di Girolamo. "A Revised Conceptual Model of the Tropical Marine Boundary Layer. Part II: Detecting Relative Humidity Layers Using Bragg Scattering from S-Band Radar". Journal of the Atmospheric Sciences 70, nr 10 (1.10.2013): 3025–46. http://dx.doi.org/10.1175/jas-d-12-0322.1.
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Abstract Persistent layers of enhanced equivalent radar reflectivity factor and reduced spectral width were commonly observed within cloud-free regions of the tropical marine boundary layer (TMBL) with the National Center for Atmospheric Research S-Pol radar during the Rain in Cumulus over the Ocean (RICO) field campaign. Bragg scattering is shown to be the primary source of these layers. Two mechanisms are proposed to explain the Bragg scattering layers (BSLs), the first involving turbulent mixing and the second involving detrainment and evaporation of cloudy air. These mechanisms imply that BSLs should exist in layers with tops (bases) defined by local relative humidity (RH) minima (maxima). The relationship between BSLs and RH is explored. An equation for the vertical gradient of radio refractivity N is derived, and a scale analysis is used to demonstrate the close relationship between vertical RH and N gradients. This is tested using the derived radar BSL boundary altitudes, 131 surface-based soundings, and 34 sets of about six near-coincident, aircraft-released dropsondes. First, dropsonde data are used to quantify the finescale variability of the RH field. Then, within limits imposed by this variability, altitudes of tops (bases) of radar BSLs are shown to agree with altitudes of RH minima (maxima). These findings imply that S-band radars can be used to track the vertical profile of RH variations as a function of time and height, that the vertical RH profile of the TMBL is highly variable over horizontal scales as small as 60 km, and that BSLs are a persistent, coherent feature that delineate aspects of TMBL mesoscale structure.
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Dimitrov, Zlatomir. "Polarimetric Analysis of ALOS PALSAR data (POL-SAR) over Test Areas in North-West Bulgaria – Polarimetric Descriptors, Decompositions and Classifications". Aerospace Research in Bulgaria 34 (2022): 29–55. http://dx.doi.org/10.3897/arb.v34.e03.
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This study is focused on utilizing full-polarimetric L-band radar data from ALOS PALSAR (JAXA) by means of Polarimetry (POL-SAR), over mountainous test sites in Bulgaria. General aim is to show feasibility of the Polarimetry to describe natural targets, which exhibits various scattering mechanisms in respect to their bio-physical and geometrical properties. Firstly, the importance of Covariance and Coherent matrices is shown, which is followed by calculation of the polarimetric coherences with their particular significance. The mathematical and physical model based decompositions are applied to describe backscattering media from scattering mechanisms. Radar indices resulted from H/A/α-decomposition showed radnomization of scattering mechanisms over forest areas, whilst two major scattering mechanisms are observed mainly in crop lands. Α comparison is made between polarimetric descriptors from acquisitions in different seasonality over mountainous forest and agricultural lands. Polarimetric segmentations and classifications are applied, with 8 (H/A) and 16 (H/A/α) components. Finally, a forest mask is proposed based on relevant polarimetric descriptors. Study showed good utilization and importance of the full-polarimetric L-band SAR data, derived from ALOS PALSAR, in natural targets and forest areas. This report resulted from a course GEO414 -“Polarimetrie”, held at the University of Jena, Lehrstuhl für Fernerkundung, in the framework of ERASMUS+, with the kind support of – Dr. T. Jagdhuber (DLR) and Prof. C. Schmullius.
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Szigarski, Christoph, Thomas Jagdhuber, Martin Baur, Christian Thiel, Marie Parrens, Jean-Pierre Wigneron, Maria Piles i Dara Entekhabi. "Analysis of the Radar Vegetation Index and Potential Improvements". Remote Sensing 10, nr 11 (9.11.2018): 1776. http://dx.doi.org/10.3390/rs10111776.
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The Radar Vegetation Index (RVI) is a well-established microwave metric of vegetation cover. The index utilizes measured linear scattering intensities from co- and cross-polarization and is normalized to ideally range from 0 to 1, increasing with vegetation cover. At long wavelengths (L-band) microwave scattering does not only contain information coming from vegetation scattering, but also from soil scattering (moisture & roughness) and therefore the standard formulation of RVI needs to be revised. Using global level SMAP L-band radar data, we illustrate that RVI runs up to 1.2, due to the pre-factor in the standard formulation not being adjusted to the scattering mechanisms at these low frequencies. Improvements on the RVI are subsequently proposed to obtain a normalized value range, to remove soil scattering influences as well as to mask out regions with dominant soil scattering at L-band (sparse or no vegetation cover). Two purely vegetation-based RVIs (called RVII and RVIII), are obtained by subtracting a forward modeled, attenuated soil scattering contribution from the measured backscattering intensities. Active and passive microwave information is used jointly to obtain the scattering contribution of the soil, using a physics-based multi-sensor approach; simulations from a particle model for polarimetric vegetation backscattering are utilized to calculate vegetation-based RVI-values without any soil scattering contribution. Results show that, due to the pre-factor in the standard formulation of RVI the index runs up to 1.2, atypical for an index normally ranging between zero and one. Correlation analysis between the improved radar vegetation indices (standard RVI and the indices with potential improvements RVII and RVIII) are used to evaluate the degree of independence of the indices from surface roughness and soil moisture contributions. The improved indices RVII and RVIII show reduced dependence on soil roughness and soil moisture. All RVI-indices examined indicate a coupled correlation to vegetation water content (plant moisture) as well as leaf area index (plant structure) and no single dependency, as often assumed. These results might improve the use of polarimetric radar signatures for mapping global vegetation.
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Bondur, Valery, Tumen Chimitdorzhiev, Aleksey Dmitriev i Pavel Dagurov. "Fusion of SAR Interferometry and Polarimetry Methods for Landslide Reactivation Study, the Bureya River (Russia) Event Case Study". Remote Sensing 13, nr 24 (17.12.2021): 5136. http://dx.doi.org/10.3390/rs13245136.
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In this paper, we demonstrate the estimation capabilities of landslide reactivation based on various SAR (Synthetic Aperture Radar) methods: Cloude-Pottier decomposition of Sentinel-1 dual polarimetry data, MT-InSAR (Multi-temporal Interferometric Synthetic Aperture Radar) techniques, and cloud computing of backscattering time series. The object of the study is the landslide in the east of Russia that took place on 11 December 2018 on the Bureya River. H-α-A polarimetric decomposition of C-band radar images not detected significant transformations of scattering mechanisms for the surface of the rupture, whereas L-band radar data show changes in scattering mechanisms before and after the main landslide. The assessment of ground displacements along the surface of the rupture in the 2019–2021 snowless periods was carried out using MT-InSAR methods. These displacements were 40 mm/year along the line of sight. The SBAS-InSAR results have allowed us to reveal displacements of great area in 2020 and 2021 snowless periods that were 30–40 mm/year along the line-of-sight. In general, the results obtained by MT-InSAR methods showed, on the one hand, the continuation of displacements along the surface of the rupture and on the other hand, some stabilization of the rate of landslide processes.
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Drews, R., O. Eisen, D. Steinhage, I. Weikusat, S. Kipfstuhl i F. Wilhelms. "Potential mechanisms for anisotropy in ice-penetrating radar data". Journal of Glaciology 58, nr 209 (2012): 613–24. http://dx.doi.org/10.3189/2012jog11j114.
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AbstractRadar data (center frequency 150 MHz) collected on the Antarctic plateau near the EPICA deep-drilling site in Dronning Maud Land vary systematically in backscattered power, depending on the azimuth antenna orientation. Backscatter extrema are aligned with the principal directions of surface strain rates and change with depth. In the upper 900m, backscatter is strongest when the antenna polarization is aligned in the direction of maximal compression, while below 900 m the maxima shift by 90° pointing towards the lateral flow dilatation. We investigate the backscatter from elongated air bubbles and a vertically varying crystal-orientation fabric (COF) using different scattering models in combination with ice-core data. We hypothesize that short-scale variations in COF are the primary mechanism for the observed anisotropy, and the 900 m boundary between the two regimes is caused by ice with varying impurity content. Observations of this kind allow the deduction of COF variations with depth and are potentially also suited to map the transition between Holocene and glacial ice.
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Monteith, Albert R., Lars M. H. Ulander i Stefano Tebaldini. "Calibration of a Ground-Based Array Radar for Tomographic Imaging of Natural Media". Remote Sensing 11, nr 24 (6.12.2019): 2924. http://dx.doi.org/10.3390/rs11242924.
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Ground-based tomographic radar measurements provide valuable knowledge about the electromagnetic scattering mechanisms and temporal variations of an observed scene and are essential in preparation for space-borne tomographic synthetic aperture radar (SAR) missions. Due to the short range between the radar antennas and a scene being observed, the tomographic radar observations are affected by several systematic errors. This article deals with the modelling and calibration of three systematic errors: mutual antenna coupling, magnitude and phase errors and the pixel-variant impulse response of the tomographic image. These errors must be compensated for so that the tomographic images represent an undistorted rendering of the scene reflectivity. New calibration methods were described, modelled and validated using experimental data. The proposed methods will be useful for future ground-based tomographic radar experiments in preparation for space-borne SAR missions.
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Yu, Tian-You, Robert D. Palmer i Phillip B. Chilson. "An investigation of scattering mechanisms and dynamics in PMSE using coherent radar imaging". Journal of Atmospheric and Solar-Terrestrial Physics 63, nr 17 (listopad 2001): 1797–810. http://dx.doi.org/10.1016/s1364-6826(01)00058-x.
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Lu, Jinwen, Yanjin Zhang, Hua Yan, Lei Zhang i Hongcheng Yin. "Global Scattering Center Representation of Target Wide-Angle Single Reflection/Diffraction Mechanisms Based on the Multiple Manifold Concept". Electronics 11, nr 24 (16.12.2022): 4209. http://dx.doi.org/10.3390/electronics11244209.
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Many radar applications, such as system design and testing and target detection and recognition, need to compress and rapidly reconstruct the target-scattering characteristics data through some suitable sparse representations, while the scattering center (SC) model resulting from different scattering mechanisms is just a prospective candidate. For the target scattering characteristics data with single reflection/diffraction mechanisms, the multimanifold structures of wide-angle SCs were revealed in light of asymptotic high-frequency theory and ray theory of electromagnetic field. Then the multimanifold clustering and curve/surface fitting algorithms are introduced to construct the target global SC (GSC) model. Compared with simulation data of sphere-cone target, the RCS at elevation 90°, azimuth 0–180° can be accurately reconstructed by only 77 parameters, the compress rate and root mean square error are 0.66 and 1.17 dB respectively. Simulation results showed that the GSC model could greatly compress the wide-angle scattering data while ensuring a suitable reconstruction accuracy. The proposed multimanifold GSC representation is convenient to implement and can effectively replace the redundant original scattering characteristics data.
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Han, Wentao, Haiqiang Fu, Jianjun Zhu, Qinghua Xie i Shurong Zhang. "Orthogonal Scattering Model-Based Three-Component Decomposition of Polarimetric SAR Data". Remote Sensing 14, nr 17 (1.09.2022): 4326. http://dx.doi.org/10.3390/rs14174326.
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New scattering models are constantly emerging to extract the detailed polarization information of ground targets. They contribute to the refined interpretation of Polarimetric Synthetic Aperture Radar (PolSAR) images. However, an increasingly prominent problem lies ahead of model decomposition methods when there are similar scattering models for a decomposition scheme. It is difficult to separate the polarization power of similar scattering mechanisms reasonably and robustly. Therefore, in this paper, we first analyze the necessity of orthogonality between scattering models. Following this, we propose two mutually orthogonal rank-1 scattering models, which can degenerate to mostly current scattering models. The orthogonality and adaptability of scattering models are considered in the model derivation. Simulated PolSAR data, real ALOS-2/PALSAR-2, GF-3, and E-SAR data are selected to validate the proposed method. As shown by the results, first, the proposed method enhances the double-bounce scattering contribution in urban areas and maintains the volume-scattering contribution in vegetation areas because it separates the polarization power of different scattering mechanisms more reasonably. Second, the proposed method is powerful in the robust interpretation of different ground targets, resulting from the orthogonality of scattering models. These two characteristics of orthogonal scattering models are expected to play a positive role in large-scale applications, especially in land-cover classification.
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Weissel, J. K., K. R. Czuchlewski i Y. Kim. "Synthetic aperture radar (SAR)-based mapping of volcanic flows: Manam Island, Papua New Guinea". Natural Hazards and Earth System Sciences 4, nr 2 (19.04.2004): 339–46. http://dx.doi.org/10.5194/nhess-4-339-2004.
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Abstract. We present new radar-based techniques for efficient identification of surface changes generated by lava and pyroclastic flows, and apply these to the 1996 eruption of Manam Volcano, Papua New Guinea. Polarimetric L- and P-band airborne synthetic aperture radar (SAR) data, along with a C-band DEM, were acquired over the volcano on 17 November 1996 during a major eruption sequence. The L-band data are analyzed for dominant scattering mechanisms on a per pixel basis using radar target decomposition techniques. A classification method is presented, and when applied to the L-band polarimetry, it readily distinguishes bare surfaces from forest cover over Manam volcano. In particular, the classification scheme identifies a post-1992 lava flow in NE Valley of Manam Island as a mainly bare surface and the underlying 1992 flow units as mainly vegetated surfaces. The Smithsonian's Global Volcanism Network reports allow us to speculate whether the bare surface is a flow dating from October or November in the early part of the late-1996 eruption sequence. This work shows that fully polarimetric SAR is sensitive to scattering mechanism changes caused by volcanic resurfacing processes such as lava and pyroclastic flows. By extension, this technique should also prove useful in mapping debris flows, ash deposits and volcanic landslides associated with major eruptions.
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Fei, Zhongyang, Yan Yang, Xiangwen Jiang, Qijun Zhao i Xi Chen. "Dynamic Electromagnetic Scattering Simulation of Tilt-Rotor Aircraft in Multiple Modes". Sensors 23, nr 17 (1.09.2023): 7606. http://dx.doi.org/10.3390/s23177606.
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To study the electromagnetic scattering of tilt-rotor aircraft during multi-mode continuous flight, a dynamic simulation approach is presented. A time-varying mesh method is established to characterize the dynamic rotation and tilting of tilt-rotor aircraft. Shooting and bouncing rays and the uniform theory of diffraction are used to calculate the multi-mode radar cross-section (RCS). And the scattering mechanisms of tilt-rotor aircraft are investigated by extracting the micro-Doppler and inverse synthetic aperture radar images. The results show that the dynamic RCS of tilt-rotor aircraft in helicopter and airplane mode exhibits obvious periodicity, and the transition mode leads to a strong specular reflection on the rotor’s upper surface, which increases the RCS with a maximum increase of about 36 dB. The maximum micro-Doppler shift has functional relationships with flight time, tilt speed, and wave incident direction. By analyzing the change patterns of maximum shift, the real-time flight state and mode can be identified. There are some significant scattering sources on the body of tilt-rotor aircraft that are distributed in a planar or point-like manner, and the importance of different scattering sources varies in different flight modes. The pre-studies on the key scattering areas can provide effective help for the stealth design of the target.
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Fan, Shengren, Vladimir Kudryavtsev, Biao Zhang, William Perrie, Bertrand Chapron i Alexis Mouche. "On C-Band Quad-Polarized Synthetic Aperture Radar Properties of Ocean Surface Currents". Remote Sensing 11, nr 19 (5.10.2019): 2321. http://dx.doi.org/10.3390/rs11192321.
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We present new results for ocean surface current signatures in dual co- and cross-polarized synthetic aperture radar (SAR) images. C-band RADARSAT-2 quad-polarized SAR ocean scenes are decomposed into resonant Bragg scattering from regular (non-breaking) surface waves and scattering from breaking waves. Surface current signatures in dual co- and cross-polarized SAR images are confirmed to be governed by the modulations due to wave breaking. Due to their small relaxation scale, short Bragg waves are almost insensitive to surface currents. Remarkably, the contrast in sensitivity of the non-polarized contribution to dual co-polarized signals is found to largely exceed, by a factor of about 3, the contrast in sensitivity of the corresponding cross-polarized signals. A possible reason for this result is the co- and cross-polarized distinct scattering mechanisms from breaking waves: for the former, quasi-specular radar returns are dominant, whereas for the latter, quasi-resonant scattering from the rough breaking crests governs the backscatter intensity. Thus, the differing sensitivity can be related to distinct spectral intervals of breaking waves contributing to co- and cross-polarized scattering in the presence of surface currents. Accordingly, routinely observed current signatures in quad-polarized SAR images essentially originate from wave breaking modulations, and polarized contrasts can therefore help quantitatively retrieve the strength of surface current gradients.
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Churyumov, A. N., Yu A. Kravtsov, O. Yu Lavrova, K. Ts Litovchenko, M. I. Mityagina i K. D. Sabinin. "Signatures of resonant and non-resonant scattering mechanisms on radar images of internal waves". International Journal of Remote Sensing 23, nr 20 (styczeń 2002): 4341–55. http://dx.doi.org/10.1080/01431160110107644.
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Chen, Si-Wei, Yong-Zhen Li, Xue-Song Wang, Shun-Ping Xiao i Motoyuki Sato. "Modeling and Interpretation of Scattering Mechanisms in Polarimetric Synthetic Aperture Radar: Advances and perspectives". IEEE Signal Processing Magazine 31, nr 4 (lipiec 2014): 79–89. http://dx.doi.org/10.1109/msp.2014.2312099.
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Nam, Christine C. W., i Johannes Quaas. "Evaluation of Clouds and Precipitation in the ECHAM5 General Circulation Model Using CALIPSO and CloudSat Satellite Data". Journal of Climate 25, nr 14 (15.07.2012): 4975–92. http://dx.doi.org/10.1175/jcli-d-11-00347.1.
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Abstract Observations from Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and CloudSat satellites are used to evaluate clouds and precipitation in the ECHAM5 general circulation model. Active lidar and radar instruments on board CALIPSO and CloudSat allow the vertical distribution of clouds and their optical properties to be studied on a global scale. To evaluate the clouds modeled by ECHAM5 with CALIPSO and CloudSat, the lidar and radar satellite simulators of the Cloud Feedback Model Intercomparison Project’s Observation Simulator Package are used. Comparison of ECHAM5 with CALIPSO and CloudSat found large-scale features resolved by the model, such as the Hadley circulation, are captured well. The lidar simulator demonstrated ECHAM5 overestimates the amount of high-level clouds, particularly optically thin clouds. High-altitude clouds in ECHAM5 consistently produced greater lidar scattering ratios compared with CALIPSO. Consequently, the lidar signal in ECHAM5 frequently attenuated high in the atmosphere. The large scattering ratios were due to an underestimation of effective ice crystal radii in ECHAM5. Doubling the effective ice crystal radii improved the scattering ratios and frequency of attenuation. Additionally, doubling the effective ice crystal radii improved the detection of ECHAM5’s highest-level clouds by the radar simulator, in better agreement with CloudSat. ECHAM5 was also shown to significantly underestimate midlevel clouds and (sub)tropical low-level clouds. The low-level clouds produced were consistently perceived by the lidar simulator as too optically thick. The radar simulator demonstrated ECHAM5 overestimates the frequency of precipitation, yet underestimates its intensity compared with CloudSat observations. These findings imply compensating mechanisms in ECHAM5 balance out the radiative imbalance caused by incorrect optical properties of clouds and consistently large hydrometeors in the atmosphere.
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Li, Haoliang, Xingchao Cui i Siwei Chen. "PolSAR Ship Detection with Optimal Polarimetric Rotation Domain Features and SVM". Remote Sensing 13, nr 19 (30.09.2021): 3932. http://dx.doi.org/10.3390/rs13193932.
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Polarimetric synthetic aperture radar (PolSAR) can obtain fully polarimetric information, which provides chances to better understand target scattering mechanisms. Ship detection is an important application of PolSAR and a number of scattering mechanism-based ship detection approaches have been established. However, the backscattering of manmade targets including ships is sensitive to the relative geometry between target orientation and radar line of sight, which makes ship detection still challenging. This work aims at mitigating this issue by target scattering diversity mining and utilization in polarimetric rotation domain with the interpretation tools of polarimetric coherence and correlation pattern techniques. The core idea is to find an optimal combination of polarimetric rotation domain features which shows the best potential to discriminate ship target and sea clutter pixel candidates. With the Relief method, six polarimetric rotation domain features derived from the polarimetric coherence and correlation patterns are selected. Then, a novel ship detection method is developed thereafter with these optimal features and the support vector machine (SVM) classifier. The underlying physics is that ship detection is equivalent to ship and sea clutter classification after the ocean and land partition. Four kinds of spaceborne PolSAR datasets from Radarsat-2 and GF-3 are used for comparison experiments. The superiority of the proposed detection methodology is clearly demonstrated. The proposed method achieves the highest figure of merit (FoM) of 99.26% and 100% for two Radarsat-2 datasets, and of 95.45% and 99.96% for two GF-3 datasets. Specially, the proposed method shows better performance to detect inshore dense ships and reserve the ship structure.
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He, Huan, Yi Chun Pan i Fang Zhi Geng. "Research on Backscattering of Sky Wave from Sea Surface". Applied Mechanics and Materials 602-605 (sierpień 2014): 2709–12. http://dx.doi.org/10.4028/www.scientific.net/amm.602-605.2709.
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For a long period, the sky-wave over-the-horizon radar (OTHR) has difficulty in detecting ship under the background of sea clutter, and it is difficult to apply the existing sea clutter model established in surface wave propagation mode to the sky-wave OTHR sea clutter suppression. Therefore, the difference between surface wave and sky wave propagation mode is analyzed firstly, then the scope of grazing angle about sky wave beam is calculated, finally the backscattering coefficients of sky wave from sea surface are derived by perturbation method and the backscattering mechanisms of sky wave from sea surface are analyzed. Results show that the mechanisms observe Bragg scattering mechanism. The backscattering coefficients of sky wave from sea surface which are given in this paper for the first time are significant for sky-wave OTHR sea clutter suppression.
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Kumjian, Matthew R., Alexander V. Ryzhkov, Heather D. Reeves i Terry J. Schuur. "A Dual-Polarization Radar Signature of Hydrometeor Refreezing in Winter Storms". Journal of Applied Meteorology and Climatology 52, nr 11 (listopad 2013): 2549–66. http://dx.doi.org/10.1175/jamc-d-12-0311.1.
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AbstractPolarimetric radar measurements in winter storms that produce ice pellets have revealed a unique signature that is indicative of ongoing hydrometeor refreezing. This refreezing signature is observed within the low-level subfreezing air as an enhancement of differential reflectivity ZDR and specific differential phase KDP and a decrease of radar reflectivity factor at horizontal polarization ZH and copolar correlation coefficient ρhv. It is distinct from the overlying melting-layer “brightband” signature and suggests that unique microphysical processes are occurring within the layer of hydrometeor refreezing. The signature is analyzed for four ice-pellet cases in central Oklahoma as observed by two polarimetric radars. A statistical analysis is performed on the characteristics of the refreezing signature for a case of particularly long duration. Several hypotheses are presented to explain the appearance of the signature, along with a summary of the pros and cons for each. It is suggested that preferential freezing of small drops and local ice generation are plausible mechanisms for the appearance of the ZDR and KDP enhancements. Polarimetric measurements and scattering calculations are used to retrieve microphysical information to explore the validity of the hypotheses. The persistence and repetitiveness of the signature suggest its potential use in operational settings to diagnose the transition between freezing rain and ice pellets.
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Battaglia, Alessandro. "Impact of second-trip echoes for space-borne high-pulse-repetition-frequency nadir-looking W-band cloud radars". Atmospheric Measurement Techniques 14, nr 12 (13.12.2021): 7809–20. http://dx.doi.org/10.5194/amt-14-7809-2021.
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Abstract. The appearance of second-trip echoes generated by mirror images over the ocean and by multiple scattering tails in correspondence with deep convective cores has been investigated for space-borne nadir-looking W-band cloud radar observations. Examples extracted from the CloudSat radar are used to demonstrate the mechanisms of formation and to validate the modelling of such returns. A statistical analysis shows that, for CloudSat observations, second-trip echoes are rare and appear only above 20 km (thus easy to remove). CloudSat climatology is then used to estimate the occurrence of second-trip echoes in the different configurations envisaged for the operations of the EarthCARE radar, which will adopt pulse repetition frequencies much higher than the one used by the CloudSat radar in order to improve its Doppler capabilities. Our findings predict that the presence of such echoes in EarthCARE observations cannot be neglected: in particular, over the ocean, mirror images will tend to populate the EarthCARE sampling window with a maximum frequency at its upper boundary. This will create an additional fake cloud cover in the upper troposphere (of the order of 3 % at the top of the sampling window and steadily decreasing moving downwards), and, in much less frequent instances, it will cause an amplification of signals in areas where clouds are already present. Multiple scattering tails will also produce second-trip echoes but with much lower frequencies: less than 1 profile out of 1000 in the tropics and practically no effects at high latitudes. At the moment, level-2 algorithms of the EarthCARE radar do not account for such occurrences. We recommend to properly remove these second-trip echoes and to correct for reflectivity enhancements, where needed. More generally this work is relevant for the design of future space-borne Doppler W-band radar missions.
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Zhang Jin-Peng, Zhang Yu-Shi, Li Qing-Liang i Wu Jia-Ji. "A time-varying Doppler spectrum model of radar sea clutter based on different scattering mechanisms". Acta Physica Sinica 67, nr 3 (2018): 034101. http://dx.doi.org/10.7498/aps.67.20171612.
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Shen, Yinbin, Xiaoshuang Ma, Shengyuan Zhu i Jiangong Xu. "Polarimetric SAR Speckle Filtering Using a Nonlocal Weighted LMMSE Filter". Sensors 21, nr 21 (6.11.2021): 7393. http://dx.doi.org/10.3390/s21217393.
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Despeckling is a key preprocessing step for applications using PolSAR data in most cases. In this paper, a technique based on a nonlocal weighted linear minimum mean-squared error (NWLMMSE) filter is proposed for polarimetric synthetic aperture radar (PolSAR) speckle filtering. In the process of filtering a pixel by the LMMSE estimator, the idea of nonlocal means is employed to evaluate the weights of the samples in the estimator, based on the statistical equalities between the neighborhoods of the sample pixels and the processed pixel. The NWLMMSE estimator is then derived. In the preliminary processing, an effective step is taken to preclassify the pixels, aiming at preserving point targets and considering the similarity of the scattering mechanisms between pixels in the subsequent filter. A simulated image and two real-world PolSAR images are used for illustration, and the experiments show that this filter is effective in speckle reduction, while effectively preserving strong point targets, edges, and the polarimetric scattering mechanism.
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Liu, Dongsheng, i Ling Han. "Integration of Fine Model-Based Decomposition and Guard Filter for Ship Detection in PolSAR Images". Sensors 21, nr 13 (23.06.2021): 4295. http://dx.doi.org/10.3390/s21134295.
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Ship detection with polarimetric synthetic aperture radar (PolSAR) has gained extensive attention due to its widespread application in maritime surveillance. Nevertheless, designing identifiable features to realize accurate ship detection is still challenging. For this purpose, a fine eight-component model-based decomposition scheme is first presented by incorporating four advanced physical scattering models, thus accurately describing the dominant and local structure scattering of ships. Through analyzing the exclusive scattering mechanisms of ships, a discriminative ship detection feature is then constructed from the derived contributions of eight kinds of scattering components. Combined with a spatial information-based guard filter, the efficacy of the feature is further amplified and thus a ship detector is proposed which fulfills the final ship detection. Several qualitative and quantitative experiments are conducted on real PolSAR data and the results demonstrate that the proposed method reaches the highest figure-of-merit (FoM) factor of 0.96, which outperforms the comparative methods in ship detection.
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Abdo, Ray, Laurent Ferro-Famil, Frederic Boutet i Sophie Allain-Bailhache. "Analysis of the Double-Bounce Interaction between a Random Volume and an Underlying Ground, Using a Controlled High-Resolution PolTomoSAR Experiment". Remote Sensing 13, nr 4 (10.02.2021): 636. http://dx.doi.org/10.3390/rs13040636.
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The radar response of vegetated environments, and forested areas in particular, are usually modeled using a very simple structure made of a random volume, representing a cloud of vegetation particles, lying over a semi-infinite medium with a rough interface, associated with the underlying ground. This Random Volume over Ground model can efficiently handle double-bounce scattering mechanisms, or arbitrary volume reflectivity profiles. This paper proposes to analyze a specific component of the Random Volume over Ground simplified scattering model, which concerns the double-bounce interaction between the ground and the volume. This specific contribution is not considered by classical characterization techniques and is studied in this work using a controlled experiment involving a Synthetic Aperture Radar operated in a Polarimetric and Tomographic configuration in order to image in 3D a controlled miniaturized scene composed of volume lying over a ground. It is shown that ground/volume double-bounce scattering, which remains focused at the ground level even in 3D imaging mode, and has polarimetric patterns that differ largely from those usually expected from double-bounce reflections, with volume-like features, such as a strong cross-polarized reflectivity or decorrelation between co-polarized channels. Moreover, it is shown that the full rank polarimetric patterns of the ground-volume mechanism are tightly linked to the reflectivity of the volume and may mask the ground response. As a consequence, isolating the ground response using 3D imaging does not permit to avoid a generally very strong distortion of the soil response by the double-bounce reflection, and the estimation of different geophysical parameters of the ground, such as its humidity or roughness are significantly altered.
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Chen, Lin, Minfeng Xing, Binbin He, Jinfei Wang, Min Xu, Yang Song i Xiaodong Huang. "Estimating Soil Moisture over Winter Wheat Fields during Growing Season Using RADARSAT-2 Data". Remote Sensing 14, nr 9 (6.05.2022): 2232. http://dx.doi.org/10.3390/rs14092232.
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Soil moisture content (SMC) is a significant factor affecting crop growth and development. However, SMC estimation, based on synthetic aperture radar (SAR), is influenced by a variety of surface parameters, such as vegetation cover and surface roughness. As a result, determining the SMC across agricultural areas (e.g., wheat fields) remotely (i.e., without ground measurement) is difficult to achieve. In this study, a model-based polarization decomposition method was used to decompose the original SAR signal into different scattering components that represented different scattering mechanisms. The different volume scattering models were applied, and then the results were compared in order to remove the scattering contribution from vegetation canopy, and extract the surface scattering components related to the soil moisture. Finally, by combining extensively used surface scattering models (e.g., CIEM and Dubois), and a method of roughness parameters optimization, a lookup table was developed to estimate the soil moisture during the wheat growth period. When CIEM is applied, the R2 and RMSE of the SMC are 0.534, 5.62 vol.%, and for the Dubois model, 0.634, 5.16 vol.%, respectively, which indicates that this approach provides good estimation performance for measuring soil moisture during the wheat growing season.
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Park, Sang-Eun, i Yoon Taek Jung. "Detection of Earthquake-Induced Building Damages Using Polarimetric SAR Data". Remote Sensing 12, nr 1 (1.01.2020): 137. http://dx.doi.org/10.3390/rs12010137.
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Remote sensing, particularly using synthetic aperture radar (SAR) systems, can be an effective tool in detecting and assessing the area and amount of building damages caused by earthquake or tsunami. Several studies have provided experimental evidence for the importance of polarimetric SAR observations in building damage detection and assessment, particularly caused by a tsunami. This study aims to evaluate the practical applicability of the polarimetric SAR observations to building damage caused by the direct ground-shaking of an earthquake. The urban areas heavily damaged by the 2016 Kumamoto earthquake in Japan have been investigated by using the polarimetric PALSAR-2 data acquired in pre- and post-earthquake conditions. Several polarimetric change detection approaches, such as the changes of polarimetric scattering powers, the matrix dissimilarity measures, and changes of the radar scattering mechanisms, were examined. Optimal damage indicators in the presence of significant natural changes, and a novel change detection method by the fuzzy-based fusion of polarimetric damage indicators are proposed. The accuracy analysis results show that the proposed automatic classification method can successfully detect the selected damaged areas with a detection rate of 90.9% and false-alarm rate of 1.3%.
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Chauhan, S., R. Darvishzadeh, M. Boschetti i A. Nelson. "UNDERSTANDING OF CROP LODGING INDUCED CHANGES IN SCATTERING MECHANISMS USING RADARSAT-2 AND SENTINEL-1 DERIVED METRICS". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLIII-B3-2020 (21.08.2020): 267–74. http://dx.doi.org/10.5194/isprs-archives-xliii-b3-2020-267-2020.
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Abstract. Crop lodging – the bending of crop stems from the vertical – is a major yield-reducing factor in cereal crops and causes deterioration in grain quality. Accurate assessment of crop lodging is important for improving estimates of crop yield losses, informing insurance loss adjusters and influencing management decisions for subsequent seasons. The role of remote sensing data, particularly synthetic aperture radar (SAR) data has been emphasized in the recent literature for crop lodging assessment. However, the effect of lodging on SAR scattering mechanisms is still unknown. Therefore, this research aims to understand the possible change in scattering mechanisms due to lodging by investigating SAR image pairs before and after lodging. We conducted the study in 26 wheat fields in the Bonifiche Ferraresi farm, located in Jolanda di Savoia, Ferrara, Italy. We measured temporal crop biophysical (e.g. crop angle) parameters and acquired multi-incidence angle RADARSAT-2 (R-2 FQ8-27° and R-2 FQ21-41°) and Sentinel-1 (S-1 40°) images corresponding to the time of field observations. We extracted metrics of SAR scattering mechanisms from RADARSAT-2 and Sentinel-1 image pairs in different zones using the unsupervised H/α decomposition algorithm and Wishart classifier. Contrasting results were obtained at different incidence angles. Bragg surface scattering increased in the case of S-1 (6.8%), R-2 FQ8 (1.8%) while at R-2 FQ21, it decreased (8%) after lodging. The change in double bounce scattering was more prominent at low incidence angle. These observations can guide future use of SAR-based information for operational crop lodging assessment in particular, and sustainable agriculture in general.
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Bailey, Johnson, i Armando Marino. "Quad-Polarimetric Multi-Scale Analysis of Icebergs in ALOS-2 SAR Data: A Comparison between Icebergs in West and East Greenland". Remote Sensing 12, nr 11 (9.06.2020): 1864. http://dx.doi.org/10.3390/rs12111864.
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Icebergs are ocean hazards which require extensive monitoring. Synthetic Aperture Radar (SAR) satellites can help with this, however, SAR backscattering is strongly influenced by the properties of icebergs, together with meteorological and environmental conditions. In this work, we used five images of quad-pol ALOS-2/PALSAR-2 SAR data to analyse 1332 icebergs in five locations in west and east Greenland. We investigate the backscatter and polarimetric behaviour, by using several observables and decompositions such as the Cloude–Pottier eigenvalue/eigenvector and Yamaguchi model-based decompositions. Our results show that those icebergs can contain a variety of scattering mechanisms at L-band. However, the most common scattering mechanism for icebergs is surface scattering, with the second most dominant volume scattering (or more generally, clouds of dipoles). In some cases, we observed a double bounce dominance, but this is not as common. Interestingly, we identified that different locations (e.g., glaciers) produce icebergs with different polarimetric characteristics. We also performed a multi-scale analysis using boxcar 5 × 5 and 11 × 11 window sizes and this revealed that depending on locations (and therefore, characteristics) icebergs can be a collection of strong scatterers that are packed in a denser or less dense way. This gives hope for using quad-pol polarimetry to provide some iceberg classifications in the future.
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Kiana, E., S. Homayouni, M. A. Sharifi i M. R. Farid-Rohani. "COMPARISON OF DECOMPOSITION METHODS OVER AGRICULTURAL FIELDS USING THE UAVSAR POLARIMETRIC SYNTHETIC APERTURE RADAR". ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XLII-4/W18 (18.10.2019): 649–53. http://dx.doi.org/10.5194/isprs-archives-xlii-4-w18-649-2019.
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Abstract. This paper investigates and compares the potential of five model-based polarimetric decompositions, namely those developed by Eigenvector-based decomposition (Van Zyl), Model-based decomposition (Freeman-Durden three-component decomposition and Yamaguchi four-component decomposition), An & Yang3 and An & Yang4 for crop biomass detection over agricultural fields covered by various crops. The time series of Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) data and the ground truth of soil and vegetation characteristics collected during the Soil Moisture Active Passive (SMAP) Validation Experiment in 2012 (SMAPVEX12) were used to compare the five decomposition methods with related to the scattering mechanisms and the biomass retrieval performances. The results show that the performance of each decomposition method for biomass retrieval depends on the crop types and the crop phenological stages. Finally, an overall biomass underestimation was observed from the five decompositions, and the highest regression value of 99% was obtained from Freeman decomposition as a result of the enhanced volume scattering. Indeed, Freeman-Durden model provided the best results.
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Miles, Richard B., James B. Michael, Christopher M. Limbach, Sean D. McGuire, Tat Loon Chng, Matthew R. Edwards, Nicholas J. DeLuca, Mikhail N. Shneider i Arthur Dogariu. "New diagnostic methods for laser plasma- and microwave-enhanced combustion". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, nr 2048 (13.08.2015): 20140338. http://dx.doi.org/10.1098/rsta.2014.0338.
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The study of pulsed laser- and microwave-induced plasma interactions with atmospheric and higher pressure combusting gases requires rapid diagnostic methods that are capable of determining the mechanisms by which these interactions are taking place. New rapid diagnostics are presented here extending the capabilities of Rayleigh and Thomson scattering and resonance-enhanced multi-photon ionization (REMPI) detection and introducing femtosecond laser-induced velocity and temperature profile imaging. Spectrally filtered Rayleigh scattering provides a method for the planar imaging of temperature fields for constant pressure interactions and line imaging of velocity, temperature and density profiles. Depolarization of Rayleigh scattering provides a measure of the dissociation fraction, and multi-wavelength line imaging enables the separation of Thomson scattering from Rayleigh scattering. Radar REMPI takes advantage of high-frequency microwave scattering from the region of laser-selected species ionization to extend REMPI to atmospheric pressures and implement it as a stand-off detection method for atomic and molecular species in combusting environments. Femtosecond laser electronic excitation tagging (FLEET) generates highly excited molecular species and dissociation through the focal zone of the laser. The prompt fluorescence from excited molecular species yields temperature profiles, and the delayed fluorescence from recombining atomic fragments yields velocity profiles.
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SURESH, R., V. ARAVINDAN, P. RAJESH RAO i A. K. BHATNAGAR. "Clear air echoes from the atmospheric boundary layer over Chennai – A study using S-band Doppler Weather Radar". MAUSAM 56, nr 2 (20.01.2022): 447–64. http://dx.doi.org/10.54302/mausam.v56i2.951.
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During December 2002 – early April 2003, between 2345 and 0215 UTC and between 1230 and 1400 UTC covering the twilight period, radar reflectivities as high as 28-38 dBZ were measured in the atmospheric boundary layer by the Doppler Weather Radar (DWR) installed at Cyclone Detection Radar station, Chennai regularly. On analysis, it was found that these radar returns were not from precipitating clouds but from some other invisible source(s). The contributory mechanisms for this high order of reflectivity have been analysed from meteorological and non-meteorological angles. Thermodynamical parameters and potential radio refractive index have been computed and analysed. The refractive index structure constant (Cn2) has been computed from the 0000 and 1200 UTC RS/RW data as well as from the radar reflectivity data. The prevalence of convectively unstable atmosphere in the first layer adjacent to the surface (upto 350 m a.g.l) at 1200 UTC and nocturnal surface inversion at 0000 UTC contribute to the enhanced Cn2 in the range of 3.58 ´ 10-12 to 10-15 m-2/3 in the layers upto 900 m a.g.l. This sort of Bragg scattering with high Cn2 could have contributed to radar reflectivity factor as high as +0.8 dBZ only. During the last three decades, there is an alarming increase in nocturnal surface inversion frequencies over Chennai presumably due to high concentration of suspended particulate matters and respirable dust particles. The contribution by these pollutants to the radar reflectivity factor is restricted to a maximum of about – 0.9 dBZ only. Migratory birds of about eight to twelve thousand in number with 10 – 50 cm2 radar cross section and possibly innumerable insects appear as sources of the enhanced reflectivity.
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Giordano, S., G. Mercier i J. P. Rudant. "A PROPOSED FRAMEWORK TO UNMIX SCATTERING MECHANISMS OF POLARIMETRIC RADAR IMAGES USING VERY HIGH RESOLUTION OPTICAL IMAGES". ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences I-7 (17.07.2012): 279–84. http://dx.doi.org/10.5194/isprsannals-i-7-279-2012.
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Bellez, S., C. Dahon i H. Roussel. "Analysis of the Main Scattering Mechanisms in Forested Areas: An Integral Representation Approach for Monostatic Radar Configurations". IEEE Transactions on Geoscience and Remote Sensing 47, nr 12 (grudzień 2009): 4153–66. http://dx.doi.org/10.1109/tgrs.2009.2023663.
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Le-Tien, T., i D. T. Nguyen. "Performance of behaviour of scattering mechanisms in time-scale domain against random noise for centimetre wave radar". Electronics Letters 33, nr 22 (1997): 1900. http://dx.doi.org/10.1049/el:19971296.
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Karachristos, Konstantinos, i Vassilis Anastassopoulos. "Land Cover Classification Based on Double Scatterer Model and Neural Networks". Geomatics 2, nr 3 (24.08.2022): 323–37. http://dx.doi.org/10.3390/geomatics2030018.
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In this paper, a supervised land cover classification is presented based on the extracted information from polarimetric synthetic aperture radar (PolSAR) images. The analysis of the polarimetric scattering matrix is accomplished according to the Double Scatterer Model which interprets each PolSAR cell by a pair of elementary scattering mechanisms. Subsequently, by utilizing the contribution rate of the two fundamental scatterers, a novel data representation is accomplished, providing great informational content. The main component of the research is to highlight the robust new feature-tool and afterwards to present a classification scheme exploiting a fully connected artificial neural network (ANN). The PolSAR images used to verify the proposed method were acquired by RADARSAT-2 and the experimental results confirm the effectiveness of the presented methodology with an overall classification accuracy of 93%, which is considered satisfactory since only four feature-vectors are used.
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Wan, Jie, Changcheng Wang, Peng Shen, Jun Hu, Haiqiang Fu i Jianjun Zhu. "Forest Height and Underlying Topography Inversion Using Polarimetric SAR Tomography Based on SKP Decomposition and Maximum Likelihood Estimation". Forests 12, nr 4 (6.04.2021): 444. http://dx.doi.org/10.3390/f12040444.
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The key point of forest height and underlying topography inversion using synthetic aperture radar tomography (TomoSAR) depends on the accurate positioning of the phase centers of different scattering mechanisms. The traditional nonparametric spectrum analysis methods (such as beamforming and Capon) have limited vertical resolution and cannot accurately distinguish closely spaced scatterers. In addition, it is very difficult to accurately estimate the ground or canopy heights with single polarimetric SAR images because there is no guarantee that the vertical profile will generate two clear and separate peaks for all resolution cells. A polarimetric TomoSAR method based on SKP (sum of Kronecker products) decomposition and iterative maximum likelihood estimation is proposed in this paper. On the one hand, the iterative maximum likelihood TomoSAR method has a higher vertical resolution than that of the traditional methods. On the other hand, the separation of the canopy scattering mechanism and the ground scattering mechanism is conducive to the positioning of the phase centers. This method was applied to the inversion of forest height and underlying topography in a tropical forest over the TropiSAR2009 test site in Paracou, French Guiana with six passes of polarimetric SAR images. The inversion accuracy of underlying topography of the proposed method was up to 1.489 m and the inversion accuracy of forest height was up to 1.765 m. Compared with the traditional polarimetric beamforming and polarimetric capon methods, the proposed method greatly improved the inversion accuracy of forest height and underlying topography.
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Li, Shengyang, Hong Tan, Zhiwen Liu, Zhuang Zhou, Yunfei Liu, Wanfeng Zhang, Kang Liu i Bangyong Qin. "Mapping High Mountain Lakes Using Space-Borne Near-Nadir SAR Observations". Remote Sensing 10, nr 9 (6.09.2018): 1418. http://dx.doi.org/10.3390/rs10091418.
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Near-nadir interferometric imaging SAR (Synthetic Aperture Radar) techniques are promising in measuring global water extent and surface height at fine spatial and temporal resolutions. The concept of near-nadir interferometric measurements was implemented in the experimental Interferometric Imaging Radar Altimeters (InIRA) mounted on Chinese Tian Gong 2 (TG-2) space laboratory. This study is focused on mapping the extent of high mountain lakes in the remote Qinghai–Tibet Plateau (QTP) areas using the InIRA observations. Theoretical simulations were first conducted to understand the scattering mechanisms under near-nadir observation geometry. It was found that water and surrounding land pixels are generally distinguishable depending on the degree of their difference in dielectric properties and surface roughness. The observed radar backscatter is also greatly influenced by incidence angles. A dynamic threshold method was then developed to detect water pixels based on the theoretical analysis and ancillary data. As assessed by the LandSat results, the overall classification accuracy is higher than 90%, though the classifications are affected by low backscatter possibly from very smooth water surface. The algorithms developed from this study can be extended to all InIRA land measurements and provide support for the similar space missions in the future.