(A) study on range migration algorithm for advanced airborne spotlight SAR imaging

Abstract

Spotlight synthetic aperture radar (SAR) can offer a high azimuth resolution than that in stripmap SAR because the antenna is properly steered to illuminate the same area during the raw data acquisition time in spotlight SAR. Thus, many researchers have developed the reconstruction algorithms for airborne spotlight SAR imaging. In this dissertation, we study the range migration algorithm (RMA) based on the spherical wave assumption and one interpolation for the spotlight SAR imaging. However, the original RMA is used in the broadside-mode monostatic SAR with the straight-line flight path. Thus, we modify the original RMA to reconstruct the SAR image with high quality in advanced spotlight SAR such as the squint-mode SAR, airborne SAR with motion errors, the bistatic SAR, the forward-looking bistatic SAR, and the airborne SAR with the high altitude. First, the RMA with the reference signal based on the fixed reference range is difficult to reconstruct the SAR image in squint-mode SAR which is used due to the flexibility of the flight path. Hence, we introduce a modified RMA with a modified reference signal to transform a squint-mode data to a broadside-mode data based on the coordinate transformation and the extended Taylor approximation (ETA). The ETA increases the accuracy of the Taylor approximation using the repetition technique. Then, using the principle of the stationary phase (PSP), we analyze the presented formulation in the frequency domain. Moreover, to compensate the curvature errors induced by the approximation of the proposed method, we extend the proposed method based on the subarea technique. Next, since a motion error is the main phase error source in airborne SAR, we introduce a modified RMA with an efficient motion compensation via the known motion error information. Specifically, the proposed method is based on the subarea technique with shifting and the subaperture technique via the mean values of the motion errors. Then, using the ETA and ...