Abstract
This paper presents a method and results for the estimation of residual Doppler frequency, and consequently the range velocity component of point targets in single-channel synthetic aperture radar (SAR) focused single-look complex (SLC) data. It is still a challenging task to precisely retrieve the radial velocity of small and slow-moving objects, which requires an approach providing precise estimates from only a limited number of samples within a few range bins. The proposed method utilizes linear least squares, along with the estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithm, to provide optimum estimates from sets of azimuth subsamples that have different azimuth temporal distances. The ratio of estimated Doppler frequency to root-mean square error (RMSE) is suggested for determining a critical threshold, optimally selecting a number of azimuth subsample sets to be involved in the estimation. The proposed method was applied to TerraSAR-X and KOMPSAT-5 X-band SAR SLC data for on-land and coastal sea estimation, with speed-controlled, truck-mounted corner reflectors and ships, respectively. The results demonstrate its performance of the method, with percent errors of less than 5%, in retrieved range velocity for both on-land and in the sea. It is also robust, even for weak targets with low peak-to-sidelobe ratios (PSLRs) and signal-to-clutter ratios (RCSs). Since the characteristics of targets and clutter on land and in the sea are different, it is recommended that the method is applied separately with different thresholds. The limitations of the approach are also discussed.
Highlights
Some multi-channel synthetic aperture radar (SAR) systems and techniques have been developed for detection and velocity retrieval of ground moving target indication (GMTI), such as along-track interferometric (ATI) systems [1,2,3,4,5,6,7]
The residual Doppler frequency in this paper is defined as a Doppler frequency of a point target residing in the single-look complex (SLC) data normally associated with the motion of the target, while the Doppler centroid represents the averaged Doppler frequency of stationary ground objects, required mainly for SAR focusing in relation to the antenna look and squint angles
To accommodate moving targets at low speed, this paper focuses on a precise estimation of the residual Doppler frequency occurring by point targets in single-channel SAR SLC data
Summary
Some multi-channel synthetic aperture radar (SAR) systems and techniques have been developed for detection and velocity retrieval of ground moving target indication (GMTI), such as along-track interferometric (ATI) systems [1,2,3,4,5,6,7]. Various space-borne single-channel SAR systems are available, but it is still challenging to utilize them for detection and velocity retrieval of ground moving targets. A precise estimation of the Doppler parameters is the key to the detection and velocity retrieval of ground moving targets by single-channel SAR observation. The main goal of this paper is to propose a high-performance method for accurate estimation of the residual Doppler frequency and the range velocity component of the point targets from the single-channel SAR focused single-look complex (SLC) data. The motivation for this study is to develop an improved residual Doppler frequency estimator for small and slow-moving targets, for instance small fishing boats and vehicles, from space-borne single channel SAR SLC data. Many sophisticated methods have been developed for GMTI, it is so far a challenging task to precisely measure the radial velocity of small and slow-moving objects from space
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