Abstract
Due to the atmospheric turbulence, the motion trajectory of airborne very high resolution (VHR) synthetic aperture radars (SARs) is inevitably affected, which introduces range-variant range cell migration (RCM) and aperture-dependent azimuth phase error (APE). Both types of errors consequently result in defocused images, as residual range- and aperture-dependent motion errors are significant in VHR-SAR images. Nevertheless, little work has been devoted to the range-variant RCM auto-correction and aperture-dependent APE auto-correction. In this paper, a precise motion compensation (MoCo) scheme for airborne VHR-SAR is studied. In the proposed scheme, the motion error is obtained from inertial measurement unit and SAR data, and compensated for with respect to both range and aperture. The proposed MoCo scheme compensates for the motion error without space-invariant approximation. Simulations and experimental data from an airborne 3.6 GHz bandwidth SAR are employed to demonstrate the validity and effectiveness of the proposed MoCo scheme.
Highlights
Since the simulation result of Point A is the same as Point D, we only present the azimuth upsampling analysis of point D in Figure 11, where “sub-ap.” refers to sub-aperture
The analysis indicates that the aperture-dependent residual motion error does affect focusing, especially toward azimuth in the very high resolution (VHR)-SAR images, and the improved sub-aperture motion compensation (MoCo) can compensate for the aperture-dependent residual motion error precisely
Experimental results based on a 3.6 GHz-bandwidth SAR are presented to demonstrate the effectiveness of the proposed MoCo scheme
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The quivering path of the airborne SAR caused by atmospheric turbulence results in a considerably blurry image, especially for very high resolution (VHR) SAR images. Traditional motion compensation (MoCo) methods for VHR-SAR are burdened by the nonnegligible errors [1]. A novel MoCo scheme including two modified IMUbased MoCo methods and two improved auto-focus methods is proposed to obtain a wellfocused VHR-SAR image for the stripmap mode by compensating offboard. Inertial measurement units (IMUs) are commonly installed on aircrafts for recording the flight trajectory. Several IMU-based motion compensation (MoCo) methods have been proposed i.e., Two Step MoCo (TSM) [2,3] and One-Step MoCo (OSM) [4,5].
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