Range Resampling in the Polar Format Algorithm for Spotlight SAR Image Formation Using the Chirp z -Transform

• Published in: IEEE transactions on signal processing Vol. 55; no. 3; pp. 1011 - 1023
• Main Authors: Zhu, Daiyin, Zhu, Zhaoda
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.03.2007; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Analog-digital conversion, digital-analog conversion, pcm coding; Applied sciences; Azimuth; Chirp; Chirp z -transform; Detection, estimation, filtering, equalization, prediction; Exact sciences and technology; Filtering; Focusing; Format; Fourier transforms; Frequency; Image processing; Information, signal and communications theory; Interpolation; PFA; polar format algorithm; range resampling; Resampling; Signal and communications theory; Signal processing; Signal, noise; Synthetic aperture radar; Telecommunications and information theory; Testing; Two dimensional displays; range resampling; Multistage method; Fourier transformation; Filtering; Chirp; AD conversion; Digitizing; Two dimensional model; Algorithm; Implementation; Interpolation; polar format algorithm; Azimuth; Simulation; Z transformation; Imaging; Radar imaging; Resampling method; Synthetic aperture radar; Chirp z-transform; Cascade connection
• ISSN: 1053-587X; 1941-0476
• DOI: 10.1109/TSP.2006.887144

Besides an inverse two-dimensional (2-D) Fourier transform, the polar format algorithm (PFA) for the spotlight synthetic aperture radar (SAR) image formation can be normally divided into two cascaded processing stages, which are called the range and azimuth resampling, respectively. This paper focuses on a new implementation of the first stage, i.e., the range resampling, using the chirp z-transform (CZT). The presented algorithm requires no interpolation. It works for the SAR system directly digitizing the echo signal, as well as that employing the dechirp-on-receive approach. The parameters of the CZT, including the frequency spacing and the start frequency, are derived to accommodate the PFA in both cases. Related filtering and compensation procedures are developed for the chirp z-transformed range signal with and without dechirp, respectively, in order to achieve a signal format entirely suitable for the azimuth resampling. Furthermore, incorporating the new algorithm with the existing CZT-based azimuth resampling and focusing algorithm, we can achieve a PFA totally free of interpolation. The presented approach has been validated by point target simulation, and the test is carried out with a very critical relative bandwidth of 30%