Abstract
Synthetic Aperture Radar (SAR) imaging with a non-zero (forward) squint angle is capable of providing a longer time for reaction than that of the broadside mode. However, due to the large squint angle, there will be severe coupling between range and azimuth samples in the echoed data, which is known as the problematic Range Cell Migration (RCM) in the SAR community. Especially when the SAR sensor mounted on an airborne platform encounters unexpected motion deviations/errors, the coupling becomes more complicated, and it is difficult to differentiate the systematic RCM for the SAR Image Formation Processing (IFP) and the non-systematic RCM error to be compensated. To this end, a novel and accurate SAR imaging algorithm is proposed in this paper to facilitate the processing of airborne SAR data collected at a high-squint angle. Firstly, the proposed algorithm is established under a Fast Time-Domain Back-Projection (FTDBP) framework for the SAR IFP. FTDBP paves the way to avoid the complicated processing for the systematic RCM as for the conventional SAR IFP in the Doppler processing manner. It is capable of generating a high-resolution SAR image efficiently under more general geometries and configurations. Secondly, regarding the non-systematic RCM errors, the proposed algorithm realizes the compensation by correcting both the Non-systematic Range Cell Migration (NsRCM), as well as Azimuthal Phase Error (APE) in a coherent manner. It is consequently capable of auto-calibrating the effects of the motion error completely without being dependent on the airborne navigation unit. Finally, both simulated and raw data collected by the airborne squinted SAR are applied to evaluate the proposed algorithm. Comparisons with conventional algorithms are carried out to reveal the superiority of the proposed algorithm.
Highlights
Synthetic Aperture Radar (SAR) has become an important tool for ground mapping and remote sensing, because of its advantages of all weather, all day-and-night, long operating range and high spatial resolution [1,2,3,4,5]
As it is well known that the accuracy of the error estimation from Azimuthal Phase Error (APE) is higher than that from the Non-systematic Range Cell Migration (NsRCM) error, we propose the motion error compensation in a coherent manner under the relationship developed in Equation (20), where the APE estimation is performed first and directly calculating the NsRCM error based on the analytical relationship
A novel error auto-calibration algorithm based on Fast Factorized Back-Projection (FFBP) formation is proposed for airborne high-resolution SAR imaging at a large squint angle
Summary
Synthetic Aperture Radar (SAR) has become an important tool for ground mapping and remote sensing, because of its advantages of all weather, all day-and-night, long operating range and high spatial resolution [1,2,3,4,5]. A novel squint SAR imaging algorithm is proposed under the FFBP IFP framework incorporated with a 2D error auto-calibration process that is capable of auto-calibrating both the APE and NsRCM errors in a coherent manner Because both the motion errors in the along-track and cross-track are taken into account, the proposed algorithm can feasibly accommodate the airborne SAR data collected at a high-squint angle. Based on the analytical relationship, the error auto-calibration process can be completed by compensating the APE and NsRCM errors coherently, instead of separately It can achieve well-focused SAR images from the echoed data collected at a high-squint angle and even without the airborne navigation measurements or when only low accuracy measurements are available.
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