Parameter Estimation and Error Calibration for Multi-Channel Beam-Steering SAR Systems

Abstract

Multi-channel beam-steering synthetic aperture radar (multi-channel BS-SAR) can achieve high resolution and wide-swath observations by combining beam-steering technology and azimuth multi-channel technology. Various imaging algorithms have been proposed for multi-channel BS-SAR but the associated parameter estimation and error calibration have received little attention. This paper focuses on errors in the main parameters in multi-channel BS-SAR (the derotation rate and constant Doppler centroid) and phase inconsistency errors. These errors can significantly reduce image quality by causing coarser resolution, radiometric degradation, and appearance of ghost targets. Accurate derotation rate estimation is important to remove the spectrum aliasing caused by beam steering, and spectrum reconstruction for multi-channel sampling requires an accurate estimate of the constant Doppler centroid and phase inconsistency errors. The time shift and scaling effect of the derotation error on the azimuth spectrum are analyzed in this paper. A method to estimate the derotation rate is presented, based on time shifting, and integrated with estimation of the constant Doppler centroid. Since the Doppler histories of azimuth targets are space-variant in multi-channel BS-SAR, the conventional estimation methods of phase inconsistency errors do not work, and we present a novel method based on minimum entropy to estimate and correct these errors. Simulations validate the proposed error estimation methods.

Unambiguous Recovery of Multistatic SAR Data for Nonzero Cross Track Baseline Case

“…The system defined by (14) is an "underdetermined" system as far as infinite number of ambiguities are taken into consideration. The proposed method can handle N amb ambiguities in the case of N = 2N amb + 1 satellites.…”

“…The number of unknowns for the reflectivity γ (r 0 − r mig k , η amb k ) is 2N amb + 1. Thus, a system of linear equations can be obtained by using N = 2N amb + 1 satellites as in (14), shown at the bottom of the page. In the vector notation (14) can be written as S = H (13) where…”

“…To overcome this limitation, a multistatic SAR reconstruction method for along-track displaced passive receivers is already proposed [12]. There are further advancements in this method to deal with higher nonuniform sampling case [3], [13] and error calibration [14]. To the best of our knowledge, the effort for combining multiple bistatic SAR data for the HRWS imaging is limited to merely along-track baselines.…”

Azimuth Multichannel Reconstruction Based on Advanced Hyperbolic Range Equation

“…Besides improving the HRWS im-aging capacity, the distributed SAR system can increase the flexibility and reliability, greatly improve the satellite operation life, and reduce the operational cost [18]. No matter how DPCMAB SAR works, azimuth multichannel reconstruction is usually required before the imaging process as improper PRF adoption leads to azimuth non-uniform sampling [19,20].…”

An Improved Airborne Multichannel SAR Imaging Method With Motion Compensation and Range-Variant Channel Mismatch Correction

“…However, as for phase error correction, the performance is dependent on the Doppler centroid frequency accuracy, and since phase error is estimated at range frequency domain, it cannot accommodate the range-variance of phase error effectively. Based on spectrum power distribution, another phase error estimation method is presented by minimizing the leaked spectrum energy caused by phase error [18]- [20]. However, the robustness of the method is relatively poor and it also has a high computational complexity, because it is sensitive to the Doppler centroid frequency error and characteristics of the scenes and an iterative operation is employed by this method.…”