A Novel Maximum-Contrast-Based Channel Phase Bias Calibration Algorithm for Spaceborne Multi-Channel SAR in Azimuth

Range-Dependent Channel Calibration for High-Resolution Wide-Swath Synthetic Aperture Radar Imagery

“…The convergence can be regulated by specifying a maximum iteration number or by evaluating the discrepancy between two consecutive iterations. It is important to observe that, when addressing the optimization problem described in Equation (22), it is necessary to compute the first-order and second-order partial derivatives at each iteration. The calculation of the inverse of the Hessian matrix, which determines the search step, is performed for each iteration and requires a significant computational burden.…”

“…The sharpness function [ 21 , 22 ] is used to calculate the overall intensity of all reconstructed Doppler components in the Doppler spectrum. This function serves as a metric for the reconstructed Doppler spectra and is dependent on the phase error parameters.…”

“…It is important to note that additional metric functions can be used to characterize the intensity distribution feature of the reconstructed Doppler spectrum. Examples include entropy, as described in [ 29 ], and contrast, as described in [ 22 ]. The primary rationale for choosing sharpness is mostly due to its convenience in deriving a simple yet effective gradient-based solver.…”

“…However, subspace projection methods require the spatial degree of freedom to be larger than the ambiguity, which, in turn, requires the use of more channels and complex equipment. The authors of [ 21 , 22 ] present a channel calibration method for HRWS SAR images. This method focuses on addressing phase errors by evaluating the sharpness of the reconstructed Doppler spectrum using a group of ideal spatial filters.…”