Abstract:Velocity bunching causes nonlinear modulations in synthetic aperture radar (SAR) images of oceanic scenes. SAR images for the azimuth waves exhibit destructive wavy patterns because of azimuthal distortion caused by velocity bunching. Meanwhile, velocity bunching creates constructive wavy patterns for long waves in certain cases. This paper aims to provide a simple indication for practical interpretation of plausible wavy patterns. A numerical simulation had been performed to address how velocity bunching form… Show more
“…Liu et al [15] suggested a method to simulate the SAR images of ship in different motion states by constructing the mesh model of the vessel, and the hydrodynamic models of the dynamic ship wake and ocean surface. Yoshida et al [16] explained the mechanism of azimuthal ocean wave emerged in SAR image spectra under specific condition based on a numerical simulation. Wang et al [17] proposed a simulation method for oceanic shear-wave-generated eddies, which was employed to research the imaging results of different radar frequencies, look directions of radar, wind speeds, and wind directions.…”
The interferometric imaging radar altimeter (InIRA) is a new generation radar altimeter, which can provide two-dimensional images of the sea surface topography (SST) at high resolution along a wide swath. This paper proposes a method for the simulation of sea surface images measured by InIRA. First, the Pierson-Moskowitz (PM) wave spectrum and two-scale model are used to simulate the sea surface from which elevation data is to be acquired. This simulated sea surface is then divided into small triangular facets using Delaunay triangulation. Second, the backscattering cross sections of these small facets are calculated via application of quasi-mirror scattering theory, and the backscattering coefficient of the simulated region derived via coherent superposition. Third, system parameters are set, consistent with the basic principle of InIRA. Assuming that the signal transmitted is a linear frequency modulation (LFM) pulse signal, the simulation images are then derived using the Range Doppler (RD) and Back Projection (BP) algorithms. By inverting the interferometric phase diagram, elevation estimates can be derived and compared with original simulated sea levels. This demonstrated accuracy within the centimeter range, verifying the correctness and feasibility of the proposed method.
“…Liu et al [15] suggested a method to simulate the SAR images of ship in different motion states by constructing the mesh model of the vessel, and the hydrodynamic models of the dynamic ship wake and ocean surface. Yoshida et al [16] explained the mechanism of azimuthal ocean wave emerged in SAR image spectra under specific condition based on a numerical simulation. Wang et al [17] proposed a simulation method for oceanic shear-wave-generated eddies, which was employed to research the imaging results of different radar frequencies, look directions of radar, wind speeds, and wind directions.…”
The interferometric imaging radar altimeter (InIRA) is a new generation radar altimeter, which can provide two-dimensional images of the sea surface topography (SST) at high resolution along a wide swath. This paper proposes a method for the simulation of sea surface images measured by InIRA. First, the Pierson-Moskowitz (PM) wave spectrum and two-scale model are used to simulate the sea surface from which elevation data is to be acquired. This simulated sea surface is then divided into small triangular facets using Delaunay triangulation. Second, the backscattering cross sections of these small facets are calculated via application of quasi-mirror scattering theory, and the backscattering coefficient of the simulated region derived via coherent superposition. Third, system parameters are set, consistent with the basic principle of InIRA. Assuming that the signal transmitted is a linear frequency modulation (LFM) pulse signal, the simulation images are then derived using the Range Doppler (RD) and Back Projection (BP) algorithms. By inverting the interferometric phase diagram, elevation estimates can be derived and compared with original simulated sea levels. This demonstrated accuracy within the centimeter range, verifying the correctness and feasibility of the proposed method.
Azimuth cutoff is an inherent disadvantage of synthetic aperture radar (SAR) wave observation. The waves shorter than some certain wavelength (azimuth cutoff) cannot be imaged in original form (structures) by SAR. For a single SAR observation, the problem of the azimuth cutoff for ocean waves can be resolved to some extent by cooperative observations of SAR satellites. Multiple SAR satellites are required to achieve simultaneous observation of an ocean area to obtain multiview SAR ocean wave synchronization data. Currently, these data cannot be acquired from in-orbit SARs. In this study, imaging simulations of multiview SAR ocean wave synchronization data based on small SAR satellites were carried out for the first time with Xband, 4-m resolution, stripmap mode and Single Look Complex (SLC) product. The Max Planck Institute (MPI) method was used to obtain the optimum wave spectrum of the synchronous data. The influencing factors of the azimuth cutoff wavelength were analyzed by using measured and simulated SAR data. The analysis results were used to develop a novel multiview wave spectrum data fusion method for azimuth cutoff compensation. The azimuth cutoff compensation effect was evaluated by comparing the inversion results before and after data fusion: the azimuth cutoff decreased by 9.76% on average, the root mean square error (RMSE) of the significant wave height is 0.06m, and RMSE of the mean wave period is 0.58s. The azimuth cutoff compensation method can be applied to SAR data for medium and low sea states (that is, wind speeds of 5-15 m/s). These results show that the proposed method of multiview wave spectrum data fusion effectively compensates for azimuth cutoff.
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