Abstract
Bistatic synthetic aperture radar (BiSAR) imaging is faced with two major challenges: large scene imaging and adaptability to unideal platform motion in practice. In order to deal with these two problems, a generalized wavefront-curvature-corrected polar format algorithm (PFA) is proposed in this article. The traditional PFA is little restricted on geometry configuration and platform motion, but its application to large scene imaging is limited by the far-field planar wavefront assumption. To solve this limitation, this article derives the phase error caused by wavefront curvature and analyzes its influence on both geometric distortion and defocusing effect in detail. Based on the analysis, we present a wavefront curvature completely correcting method through space-variant phase compensation using the analytical wavefront curvature phase in wavenumber-domain, which is derived through method of series reversion. What's more, an efficient realization of the space-variant phase compensation based on two-stage image division is given to avoid high overlap rate in the traditional image division method. The proposed method can obtain well focused and geometric undistorted image for BiSAR under complicated flight paths, and it also keeps the logarithmic complexity of traditional PFA. The effectiveness of the proposed method is verified by numerical simulations.
Highlights
B ISTATIC synthetic aperture radar (BiSAR) has the unique advantage of flexible imaging geometry configuration, it can be applied to earth remote sensing and reconnaissance in various application modes such as forward-looking, spotlight or strip-map, etc
For BiSAR, polar format algorithm (PFA) can work well in small scene size imaging with respect to the focusing effect despite slight geometric distortion
These simulation results well indicates that the proposed method can greatly expand the effective scene size for BiSAR with complicated flight paths compared with the existing results of PFA and eliminate geometric distortion
Summary
B ISTATIC synthetic aperture radar (BiSAR) has the unique advantage of flexible imaging geometry configuration, it can be applied to earth remote sensing and reconnaissance in various application modes such as forward-looking, spotlight or strip-map, etc. Higher-order trajectories may result in higher quadratic phase error (QPE) compared to cases with linear trajectories, which greatly reduces the valid imaging scene-size for traditional imaging algorithms Methods with both efficiency and adaptability to complicated flight paths are needed to be researched. Different from traditional frequency domain imaging methods, this algorithm multiplies the echo signal by the reference function in azimuth time and range frequency domain, it can well adapt to BiSAR with various geometries (including forward-looking) and even with complicated flight paths in the same way as BPA. We propose a generalized wavefront-curvaturecorrected PFA that is applicable for BiSAR with complicated platform motion The trajectories of both the receiver and the transmitter are assumed to be high-order polynomials of azimuth time.
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