Abstract
This paper presents a new approach for the squint-mode spotlight SAR imaging. Like the frequency scaling algorithm, this method starts with the received signal dechirped in range. According to the geometry for the squint mode, the reference range of the dechirping function is defined as the range between the scene center and the synthetic aperture center. In our work, the residual video phase is compensated firstly to facilitate the following processing. Then the range-cell migration with a high-order range-azimuth coupling form is processed by a nonlinear frequency scaling operation, which is different from the original frequency scaling one. Due to these improvements, the algorithm can be used to process high squint SAR data with a wide swath and a high resolution. In addition, some simulation results are given at the end of this paper to demonstrate the validity of the proposed method.
Highlights
Spotlight synthetic aperture radar (SAR) often operates in the squint mode
A simple geometry of airborne squint mode spotlight SAR is shown in Figure 1, where h is the flight altitude, θ is the angle of view, rc is the distance from the center of the scene to the flight line, rmin and rmax are the minimum and maximum distance from the scene to the flight line, and Rc is the distance between the scene center and the synthetic aperture center
The results obtained by using the frequency scaling (FS) algorithm [4], the FS algorithm with the dechirping function given in this paper and the proposed algorithm, have been compared
Summary
Several algorithms can be used for the squint mode spotlight SAR processing, that is, the polar format algorithm (PFA) [1], the range migration algorithm (RMA) [2], the chirp scaling (CS) algorithm [3], and the frequency scaling (FS) algorithm [4], the former three of which have been comprehensively discussed in [5]. With increasing the squint angle, the error becomes significant and degrades the image In the latter algorithm, which is presented specially for spotlight SAR data processing, the dechirped signal has been applied to reduce the sampling frequency in range. Based on the CS algorithm, a nonlinear chirp scaling (NCS) algorithm [8] has been proposed to deal with the squint mode strip-map SAR imaging, in which the CS technique is extended to the cubic order to achieve the effect of the rangedependent filtering required in the SRC.
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