Channel Phase Calibration for High-Resolution and Wide-Swath SAR Imaging with Doppler Spectrum Sharpness Optimization

Abstract

Channel phase calibration is a crucial issue in high resolution and wide swath (HRWS) imagery with azimuth multi-channel synthetic aperture radar (SAR) systems. Precise phase calibration is definitely required in reconstructing the full Doppler spectrum for precise HRWS imagery without high-level ambiguities. In this paper, we propose a novel calibration for HRWS SAR imagery by optimizing the reconstructed unambiguous Doppler spectrum. The sharpness of the reconstructed Doppler spectrum is applied as the metric to measure the unambiguity quality, which is maximized to retrieve the element phase error caused by channel imbalance. Real data experiments demonstrate the performance of the proposed calibration for ambiguity suppression in HRWS SAR imagery.

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

“…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.…”

“…The primary rationale for choosing sharpness is mostly due to its convenience in deriving a simple yet effective gradient-based solver. The solution developed by Newton is a convenient and highly efficient method for obtaining an optimal estimation [ 21 ]. We implement an iterative gradient-based solver in the following content.…”

“…Based on the given values, the distance between two adjacent channels in the array is approximately 8.427 m. In addition, a transmit bandwidth of 30 MHz yields a range resolution of 5 m. With 2048 range samples, this results in a range width of approximately 10.24 km. In our simulation experiments, we compare our proposed algorithm with the subspace projection algorithm [ 20 ] and the range-independent maximum spectrum sharpness (RIDMSS) algorithm from [ 21 ]. To conduct the comparison, we set the Doppler ambiguity number to three and the number of channels to four.…”

“…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.…”