Research On Synthetic Aperture Radar Imaging Simulation From The Maritime Scene

The research on synthetic aperture radar (SAR) imaging simulation from the maritimescene has important scientific significance in the ocean environment monitoring, targetdetection and separation technology of signal. It is an important way to improve theperformance of SAR systems, verify SAR imaging algorithm and enhance the effect of theSAR application. The related works are systematically researched in this paper.The ocean surface wave model for SAR imaging is discussed firstly. The structure of theocean surface, which can be “seen” by the SAR, and the mechanism of the SAR to detectlarge-scale surface waves are studied. Ocean surface waves are described by the fluidmechanics model of water wave point. And, for ocean surface waves with obviousrandomness, it can be described by the superposition of waves with different amplitudes,frequencies, directions and phases. Two-scale surface model and the latest findings areintroduced.Two high-resolution SAR imaging processing algorithms are presented: range Doppler(RD) algorithm and chirp scaling (CS) algorithm, whose performances are compared. On thebasis of this, an improved non-linear chip scaling (NLCS) approach is proposed to handle thegeneral bistatic SAR (Bis-SAR) data to overcome the limitations of normal approach. The keyis to achieve the accurate spectrum of signal obtained by the method of series reversion andreduce the range-azimuth coupling by the linear range cell migration correction (LRCMC).Then the data is handled by NLCS, so the azimuth compression is enabled. Simulation resultsshow that the improved NLCS method can handle the complex Bis-SAR data.SAR imaging mechanism of ocean waves is investigated in detail. For SAR systems canonly probe the microscale waves which can emerge Bragg resonance with the incidentelectromagnetic (EM) wave. And, mesoscale ocean phenomena (such as surface waves,internal waves, under water topography and ships trails, etc.) can only be obtained by SARsystems indirectly through the modulation to microscale waves in space and time. The impactof spatial modulation and time modulation to SAR imaging is discussed in detail. In view ofthe inaccuracy of spectra modulation, a modulated distributed surface facet model (MDSFM)is proposed to calculate the radar cross section (RCS) of ocean surface in synthetic aperturetime based on the efficient double superimposition model (DSM). The modulation mechanismof ocean wave on SAR imaging is discussed in detail combined with calculation in spatialdomain and modulation in spectral domain. So the accurate SAR imaging simulation of oceanwaves is achieved. In addition, the impact of breaking waves on SAR imaging is discussed. Further, a hybrid method based on physical optics (PO) and physical theory of diffraction withequivalent edge currents (PTDEEC) is presented to calculate the high frequency scatteringcharacteristics of large ship target. Finally, this hybrid method combines with the four-pathmodel and MDSFM to investigate SAR imaging mechanism for the composite model of shipon dynamic ocean scene.Imaging mechanisms of Along-track interferometric synthetic aperture radar (ATI-SAR)and across-track interferometric synthetic aperture radar (XTI-SAR) for ocean waves arestudied in detail to analyze the application of this new technology on marine remote sensing.The complex image of ATI-SAR and XTI-SAR for ocean waves and the non-linear mappingbetween ATI-SAR phase spectra and wave spectral are obtained.For the more complicated geometry of marine Bis-SAR systems related to the marineMon-SAR systems, the modulated distributed surface facet moel (MDSFM) is extended tobistatic case. In addition, the impact of velocity bunching (VB) modulation, which is theunique modulation mechanism for SAR, on Bis-SAR is researched. The composite EMscattering between the ocean surface and the complex targets is calculated by the analysis ofthe bistatic scattering mechanism to obtain the scattering echo data of Bis-SAR. The intensityexpression in Bis-SAR image plane is derived which quantificationally describes the azimuthdisplacement of the scatter elements, the azimuth degradation of radar resolution and therange degradation of radar resolution caused by composite scattering. It provides a theoreticalbasis for the system design and applied research in ocean remote sensing of the Bis-SAR.A more accurate SAR raw echo model is obtained by improving the model proposed byFranceschetti. It overcomes the imprecise problem caused by the spectrum only to considergravity and the scattering coefficient only to take KA approximation. Then thethree-dimensional (3-D) convolution in time-domain (TD) is replaced by two-dimensional(2-D) product in frequency-domain (FD) by using the Fast Fourier Transform (FFT) and thedispersion relation of sea spectrum. The computational efficiency is greatly improved by thismodel, so the feasibility and accuracy of SAR raw echo data simulation for extended oceanscene is improved.