Abstract
The coupling between range and azimuth dimensions is the main obstacle for highly squinted synthetic aperture radar (SAR) data focusing. Range walk correction (RWC) processing is effective to remove the linear coupling term, but the residual high order range cell migration (RCM) parts are spatial-variant in both range and azimuth dimensions. In this paper, we propose a precise spatial-variant range cell migration correction (RCMC) method with subaperture processing. The method contains two stages. Firstly, the main component of range-variant RCM is corrected in the coarse RCMC stage. Secondly, data are derived into azimuth subapertures (SAs), an SA-image-domain RCMC is developed by interp correction, where the SA image is obtained using a modified spectrum analysis (SPECAN) algorithm by establishing the relationship between Doppler frequency and residual spatial-variant RCM. In the proposed algorithm, precise compensation of space-variant RCM is implemented by SA processing, which is designed for a better practicality in real-time processing system. Simulated and real measured data experiments are designed to validate the effectiveness of the proposed approach for highly squinted SAR imaging.
Highlights
The highly squinted operating model [1,2] is widely used in the practical application of airborne synthetic aperture radar (SAR) [3], which has the advantages of higher mobility and flexibility to observe the areas of interest
After Range walk correction (RWC) processing, the main component of range-variant range cell migration (RCM) is corrected in the coarse range cell migration correction (RCMC) stage by range chirp scaling algorithm (CSA)
The azimuth nonlinear chirp scaling (ANLCS) processing provides highly accurate azimuth compression after RCMC with both CSA and the proposal, the focus degradation caused by the residual spatial-variant RCM in the CSA formation is significant enough to cause geometric and radiometric resolution losses
Summary
The highly squinted operating model [1,2] is widely used in the practical application of airborne synthetic aperture radar (SAR) [3], which has the advantages of higher mobility and flexibility to observe the areas of interest. For highly squinted SAR imaging, the most accurate method is based on time domain processing, such as backprojection (BP) and its extended fast imaging algorithms [9,10,11]. Based on the principle that azimuth times corresponding to the same Doppler frequency are different for targets in the same range cell, an effective SA azimuth-variant RCM compensation method is proposed in [28]. Based on the analysis above, an SA processing-based method is investigated in this paper, which implements the accurate azimuth-variant RCM compensation for highly squinted SAR. In the azimuth SPECAN image domain, the azimuth-variant residual RCM is easy to compensate by integrally shifting the image in the range direction according to the azimuth coordinate This step is rapidly implemented by interp correction processing. We would theoretically analyze the problem of conventional decoupling process in the following subsections
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