Focusing Bistatic SAR Data Using the Nonlinear Chirp Scaling Algorithm

Abstract

Abstract-Bistatic synthetic aperture radar data are more challenging to process than the common monostatic counterparts because the flight geometry is more complicated and the data are usually nonstationary. Whereas time-domain algorithms can handle general bistatic cases, they are very inefficient; therefore, frequency-domain methods are preferred. Several frequencydomain monostatic algorithms have been modified to handle a limited number of bistatic cases, but a general algorithm is sought, which can handle cases such as nonequal platform velocities, nonparallel flight tracks, and high squints. In this paper, we modify the nonlinear chirp scaling (NLCS) algorithm to handle a general case of bistatic data. The key is to use a linear range cell migration correction to reduce the range-azimuth coupling, an NLCS to precondition the data for azimuth compression, and a series expansion to obtain an accurate form of the signal spectrum. The azimuth nonstationarity is handled through the use of invariance regions. Simulations have shown that the modified NLCS algorithm can handle data with more complicated bistatic geometries than the previous algorithms.Index Terms-Bistatic SAR, chirp scaling, perturbation function, point target response, range cell migration (RCM) correction (RCMC), secondary range compression (SRC), synthetic aperture radar (SAR).

Azimuth-Variant Signal Processing in High-Altitude Platform Passive SAR with Spaceborne/Airborne Transmitter

“…Several algorithms have been developed based on this model [39]. Another BiSAR spectrum model using series expansion to express azimuth time as a function of azimuth frequency during azimuth Fourier transform was proposed in [40], and a chirp scaling algorithm was developed based on this model [41]. However, the accuracy is controlled by keeping enough terms in the power series, but only the first several series can be used.…”

“…Next, a NCS algorithm, which is similar to the algorithms developed in [35,41], can then be applied. Our algorithm has the processing steps similar to [35,41], but has different compensation phase terms, Φ i (i = [1,2,3,4,5]), because the azimuth-variant Doppler characteristics are considered in deriving the algorithm. Suppose the transmitted signal is…”

Focusing Translational Variant Bistatic Forward-Looking SAR Using Keystone Transform and Extended Nonlinear Chirp Scaling

“…Nonlinear chirp scaling (NLCS) was first adopted by Wong and Yeo in monostatic and bistatic SAR data processing [23]. Current publications on bistatic SAR NLCS algorithm can be found in References [31][32][33][34]. In Qiu et al [34], an azimuth NLCS algorithm based on numerical fitting is proposed to process bistatic SAR data with a stationary transmitter.…”

Two-Dimensional Spectrum for BiSAR Derivation Based on Lagrange Inversion Theorem

“…The former refers to the backprojection algorithms [1], [2] where all calculations are implemented in time-domain. On the contrary, all processing steps of the latter such as Range Doppler (RD) [3], Chirp Scaling (CS) [4] are performed in one-dimension and/or twodimension frequency-domain. Since Fast Fourier Transform (FFT) is always utilized in the these algorithms, they are also called the FFT-based algorithms.…”

“…The RD and CS algorithms [3], [4] are directly developed on this two-dimensional spectrum. The aim of this study is to derive a new two-dimensional spectrum for bistatic SAR based on the commonly used mathematic principles such as the method of stationary phase and the Fourier transform.…”