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Luke Rosenberg - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Medium Grazing Angle X-band
2020Co-Authors: Luke Rosenberg, Nick J. StacyAbstract:Doppler analysis of radar sea-clutter is typically performed from a static cliff top location looking out to sea. This constrains the Grazing Angle to low values and the radar look direction with respect to the wind. Current research at the DSTO is interested in the properties of sea- clutter at medium to high Grazing Angles, over all azimuth directions, full polarisation and different spatial resolutions. The sea clutter Doppler spectrum investigated in this paper was collected by an airborne platform and analysed using the three component Walker scattering model modified to include Doppler shifts from the moving platform. The modelling results enable the underlying Doppler spectrum and autocorrelation of the sea clutter to be estimated. This will enable future analysis into the performance of medium to high Grazing Angle target detection algorithms in the maritime environment. Index Terms—Sea-clutter, SAR, Doppler
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Investigation of Azimuthal Variations From X-Band Medium-Grazing-Angle Sea Clutter
IEEE Transactions on Geoscience and Remote Sensing, 2016Co-Authors: Zaynab Guerraou, Luke Rosenberg, Sébastien Angelliaume, Charles-antoine GuérinAbstract:The Ingara X-band fully polarimetric medium-Grazing-Angle sea-clutter data set was collected in the Australian maritime environment over an angular range of 360° in azimuth and from 15° to 45° in Grazing. This paper reports further analysis of this data set, focusing on understanding the azimuth variation to enable improved simulation accuracy and extraction of relevant geophysical parameters. This includes some original properties of the co- and cross-polarized normalized radar cross section as a function of the scattering geometry and sea surface parameters. We also assess the performances and limitations of recent sea surface scattering models in the light of this rich data set.
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doppler spectra of medium Grazing Angle sea clutter part 1 characterisation
Iet Radar Sonar and Navigation, 2016Co-Authors: Simon Watts, Luke Rosenberg, Stephen Bocquet, Matthew RitchieAbstract:This study is concerned with the characterisation of Doppler spectra from high range resolution X-band radar sea clutter observed from an airborne platform over the range of Grazing Angles, 15° to 45°. It is observed that when looking up or down wind there is a strong correlation between mean Doppler shift and local spectrum intensity. When combined with random fluctuations of spectrum width, these characteristics give the spectra a temporal and spatial variability. This behaviour has previously been observed in low Grazing Angle data and these results confirm the wider applicability of the models developed using that data. The modelling method is also extended here to capture the bimodal behaviour observed with high intensity returns from breaking waves looking up or down-wind.
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Statistical analysis of low Grazing Angle high resolution X-band SAR sea clutter
2014 International Radar Conference, 2014Co-Authors: Anthony Fiche, Luke Rosenberg, Sébastien Angelliaume, Ali KhenchafAbstract:This paper investigates the statistical analysis of two low Grazing Angle (3° and 10°) synthetic aperture radar datasets collected by ONERA's SETHI X-band radar off the coast of France. The focus of the work is to find the most suitable probability density function which matches the data. Particular attention is paid to the tail region, where the threshold is determined in a detection scenario. To measure the effectiveness of each model fit, the Bhattacharyya metric has been extended to measure the goodness of fit in this region.
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Coherent detection with non-stationary high Grazing Angle X-band sea-clutter
2014 11th European Radar Conference, 2014Co-Authors: Luke RosenbergAbstract:The detection of radar targets in non-stationary sea-clutter is an important research problem for the radar community. A successful detection scheme should take account of the first and second order statistics, maintain a constant false alarm rate and have a relatively simple processing scheme. Three detection scenarios based on the cell averaging constant false alarm rate (CA-CFAR) algorithm are investigated in this paper using the Ingara high Grazing Angle data. The first two apply the CA-CFAR algorithm in the time and frequency domains, while the third uses the output of an adaptive least squares filter applied to adaptively whiten the data.
H. Rungaldier - One of the best experts on this subject based on the ideXlab platform.
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Wind-speed dependence of small-Grazing-Angle microwave backscatter from sea surfaces
IEEE Transactions on Antennas and Propagation, 1996Co-Authors: J.d. Barter, B.m. Lake, E. Caponi, M. Caponi, C.l. Hindman, H. RungaldierAbstract:Results of X-band microwave backscatter from sea surfaces at a small-Grazing Angle for a range of wind speeds (3.8-10.3 m/s) are presented. The data indicate that the speed of faster-than-Bragg scatterers and their time-averaged polarization ratio both increase with wind speed. At a friction velocity above /spl sim/21 cm/s, super events (i.e., backscattering events where the horizontal-polarization power exceeds the vertical-polarization power) begin to appear. The fraction of fast scatterers which produce super events also increases with wind speed. The presence of super events indicates that in addition to scattering mechanisms, such as Bragg-resonant scattering, composite surface theory, wedge scattering, and specular reflection, other mechanisms which favor the horizontal-polarization returns must be considered.
B.m. Lake - One of the best experts on this subject based on the ideXlab platform.
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Hydrodynamic effects in low-Grazing Angle backscattering from the ocean
IEEE Transactions on Antennas and Propagation, 1999Co-Authors: E.a. Caponi, B.m. Lake, H.c. YuenAbstract:Time series of returned power, Doppler spectra and range versus time intensity (RTI) images collected from low-Grazing Angle radar backscattering from the ocean present features which cannot be explained solely within the framework of resonant Bragg scattering. We propose that most of the observed characteristics are a consequence of the way in which waves evolve on the surface of the ocean. We have built a model consisting of a hydrodynamic module and a radar response module. The hydrodynamics module includes most of the physics thought to be relevant to the evolution of a wavefield (i.e., nonlinear interactions, wind, and wavebreaking). The radar module computes the backscattering as the accumulation of Bragg response from every tilted facet of the reconstructed surface, except for those locations where hydrodynamic conditions leading to wavebreaking are detected. Facets involved in wavebreaking are assumed to contribute to the backscattering in a quasi-specular polarization independent fashion. The hydrodynamics module is used to simulate the evolution of a nonlinear wave field, starting from essentially monochromatic conditions. The evolution reproduces known characteristics of these systems, including the generation of sideband instabilities and downshifting. The radar response module is then exercised on the resulting surface at various stages of development. Simulated RTIs at very low-Grazing Angles reproduce the observed polarimetric characteristics, as well as their behavior when the Grazing Angle is increased. Simulated Doppler spectra reproduce the peak separation phenomenon observed in field measurements at very low-Grazing Angles and also show a behavior similar to that shown by field data when the Grazing Angle is increased.
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Wind-speed dependence of small-Grazing-Angle microwave backscatter from sea surfaces
IEEE Transactions on Antennas and Propagation, 1996Co-Authors: J.d. Barter, B.m. Lake, E. Caponi, M. Caponi, C.l. Hindman, H. RungaldierAbstract:Results of X-band microwave backscatter from sea surfaces at a small-Grazing Angle for a range of wind speeds (3.8-10.3 m/s) are presented. The data indicate that the speed of faster-than-Bragg scatterers and their time-averaged polarization ratio both increase with wind speed. At a friction velocity above /spl sim/21 cm/s, super events (i.e., backscattering events where the horizontal-polarization power exceeds the vertical-polarization power) begin to appear. The fraction of fast scatterers which produce super events also increases with wind speed. The presence of super events indicates that in addition to scattering mechanisms, such as Bragg-resonant scattering, composite surface theory, wedge scattering, and specular reflection, other mechanisms which favor the horizontal-polarization returns must be considered.
D.b. Trizna - One of the best experts on this subject based on the ideXlab platform.
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Dual polarized RCS Grazing Angle characteristics of internal gravity waves
IGARSS '98. Sensing and Managing the Environment. 1998 IEEE International Geoscience and Remote Sensing. Symposium Proceedings. (Cat. No.98CH36174), 1998Co-Authors: D.b. TriznaAbstract:Grazing Angle dependencies of radar cross section (RCS) are shown to differ for horizontally (HH) and vertically (VV) polarized X-band marine radar sea scatter from internal gravity wave (IGW) spatial modulations. For these internal gravity waves, observed off the coast of North Carolina, an IGW crest-to-trough modulation of 30-dB is observed at HH at 1/spl deg/, but only 10 dB at VV. The HH RCS decreases with increasing Grazing Angle, roughly to the minus one power, whereas VV RCS increases as for the composite model, but only to the first power. The HH/VV RCS ratio is 10 dB at 1/spl deg/, again opposite that expected from the two scale model, and decreases to -10 dB at 10/spl deg/ Grazing. The two scale model with wave-current modulation of short waves by wave-current interaction predicts a decrease in modulation as Grazing is approached, opposite the results presented. The authors suggest an influence of wave breaking radar scatter sources to explain these internal wave results, similar to arguments made for breaking wave scatter occurring near fronts.
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Low Grazing Angle dual polarized Doppler radar measurements of oceanic fronts
IGARSS '96. 1996 International Geoscience and Remote Sensing Symposium, 1996Co-Authors: N. Allan, D.b. Trizna, D.j. MclaughlinAbstract:Presents low Grazing Angle dual polarized Doppler radar measurements of oceanic fronts made from a ship-borne platform during the 2nd ONR/NRL High Resolution Remote Sensing experiment (HIRES-II). These are compared with in-situ Acoustic Doppler Current Profiler (ADCP) measurements and occurrence of whitecap events recorded using a closed circuit TV camera. The results show that dual polarized radar operating in this angular regime can provide useful information about the current variability, occurrence of wave breaking and the effects of fronts on the propagation of ocean waves. This information is important for understanding and modeling the physical mechanisms governing the radar imaging of oceanic fronts.
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High resolution polarimetric radar scattering measurements of low Grazing Angle sea clutter
IEEE Journal of Oceanic Engineering, 1995Co-Authors: D.j. Mclaughlin, E.m. Twarog, N. Allan, D.b. TriznaAbstract:This paper presents fully polarimetric radar scattering measurements of low Grazing Angle sea clutter. The measurements were obtained at a three degree Grazing Angle using a high range resolution (1.5 m) X-Band polarimetric radar operated from a shore site overlooking the Chesapeake Bay. The radar employs pulse-to-pulse switching between orthogonal transmitted polarizations and simultaneously measures two orthogonally polarized components of the backscattered wave to obtain full polarimetric information about the scattering process. The complete Stokes matrix, computed by averaging successive realizations of the polarization scattering matrix, is used to obtain polarization signatures and to determine the polarization dependence of the clutter. Sea spike echoes are shown to be weakly polarized and to exhibit polarization signatures indicative of multiple independent scattering mechanisms. Clutter echoes in the absence of sea spikes are shown to be highly polarized and to exhibit polarization signatures indicative of a single dominant scattering mechanism.
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Statistics of X and S-band low Grazing Angle radar sea scatter
Proceedings of IGARSS '93 - IEEE International Geoscience and Remote Sensing Symposium, 1993Co-Authors: D.b. TriznaAbstract:Presents results of low Grazing Angle sea scatter experiments conducted using horizontally polarized, X and S-band radars for relatively calm seas and light winds. Comparisons are shown of the cumulative distributions of normalized radar cross section (NRCS) as a function of Grazing Angle. Differences at large NRCS suggest that scattering mechanisms in addition to Bragg scatter are more important at X-band than S-band.
Xiaojian Xu - One of the best experts on this subject based on the ideXlab platform.
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Simulation of Correlated Low-Grazing-Angle Sea Clutter Based on Phase Retrieval
IEEE Transactions on Geoscience and Remote Sensing, 2015Co-Authors: Jianing Wang, Xiaojian XuAbstract:It is known that the major difficulty of sea clutter simulation is the controlled generation of a continuous correlated non-Gaussian random process. In particular, for sea clutter at low Grazing Angles and over a long time scale, the spiky and nonstationary nature makes the simulation more difficult. This paper proposes a novel procedure for the simulation of continuous correlated low-Grazing-Angle sea clutter with prescribed statistic and correlation characteristics. The Pareto distribution is utilized to describe the statistics of the sea clutter intensity. In addition, different correlation characteristics for sea clutter over both short and long time scales are considered in this paper. First, the memoryless nonlinear transform is adopted to simulate the intensities of the correlated sea clutter. Second, the Doppler spectra of different range bins are generated separately. In particular, for the sea clutter over long time scales, successive time-varying Doppler spectra are modeled to characterize the nonstationarity of the sea clutter series. Then, the phases of the sea clutter are retrieved by constraining to the desired Doppler spectra and given magnitudes. Different methods are adopted for the phase retrieval of sea clutter on short and long time scales. Finally, simulation results show that the proposed procedure can generate continuous low-Grazing-Angle sea clutter with prescribed statistic and correlation characteristics. In particular, for the sea clutter over a long time scale, the simulated sea clutter series enjoys the time-varying Doppler spectrum while maintaining continuity. In addition, the proposed method is also suitable for other models, such as the K-distribution, the Weibull model, and so on.
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Simulation of Pareto distributed temporally and spatially correlated low Grazing Angle sea clutter
2014 International Radar Conference, 2014Co-Authors: Jianing Wang, Xiaojian XuAbstract:This paper proposes a procedure for simulation of the temporally and spatially correlated low Grazing Angle sea clutter based on the statistical and correlated characteristics. The magnitudes are Pareto distributed and the temporal correlation characteristics in separated range bins are different from each other. Firstly, the memoryless nonlinear transform (MNLT) is adopted to directly simulate the Pareto distributed high resolution range profiles (HRRPs) of the temporally and spatially correlated sea clutter from coherent pulses. Secondly, by utilizing the approximately linear relationship between the central Doppler frequency and the magnitude of low Grazing Angle sea clutter, Doppler spectrum of each range bin is modeled. Then, the alternating projection (AP) approach is used to retrieve the phases of sea clutter with desired Doppler spectrum and given magnitudes. Finally, simulation results show the Pareto distributed temporally and spatially correlated sea clutter with desired spatial correlation function and range resolved Doppler spectra.
