Abstract
Multichannel synthetic aperture radar (SAR) is a significant breakthrough to the inherent limitation between high-resolution and wide-swath (HRWS) compared with conventional SAR. Moving target indication (MTI) is an important application of spaceborne HRWS SAR systems. In contrast to previous studies of SAR MTI, the HRWS SAR mainly faces the problem of under-sampled data of each channel, causing single-channel imaging and processing to be infeasible. In this study, the estimation of velocity is equivalent to the estimation of the cone angle according to their relationship. The maximum likelihood (ML) based algorithm is proposed to estimate the radial velocity in the existence of Doppler ambiguities. After that, the signal reconstruction and compensation for the phase offset caused by radial velocity are processed for a moving target. Finally, the traditional imaging algorithm is applied to obtain a focused moving target image. Experiments are conducted to evaluate the accuracy and effectiveness of the estimator under different signal-to-noise ratios (SNR). Furthermore, the performance is analyzed with respect to the motion ship that experiences interference due to different distributions of sea clutter. The results verify that the proposed algorithm is accurate and efficient with low computational complexity. This paper aims at providing a solution to the velocity estimation problem in the future HRWS SAR systems with multiple receive channels.
Highlights
Remote sensing for civilian and military applications sets a high requirement on both the spatial resolution and swath coverage for synthetic aperture radar (SAR)
We propose a novel algorithm for velocity estimation and unambiguous imaging of the moving target in a spaceborne high-resolution and wide-swath (HRWS) SAR system
Phase offsets among channels effectiveness is evaluated by the proximity of the root mean squired error (RMSE) to the Cramér–Rao lower bound (CRLB)
Summary
Remote sensing for civilian and military applications sets a high requirement on both the spatial resolution and swath coverage for synthetic aperture radar (SAR). Conventional SAR systems can barely achieve high-resolution and wide-swath (HRWS) images simultaneously [1]. Higher pulse repetition frequency (PRF) is needed to obtain higher azimuth resolution, while lower PRF is required to acquire a wider range swath. The launch of the TerraSAR-X satellite in 2007 [3], the ALOS-2 satellite in 2014 [4], and the Chinese Gaofen-3 satellite in 2016, which all contain a dual-receive channel mode, demonstrated the feasibility of this technique. Spaceborne HRWS SAR with more receive channels is one of the prospects of SAR systems. Moving target indication and imaging is one of the primary applications of spaceborne HRWS SAR systems, especially for ocean remote sensing [2,3]. Estimation of the target’s velocity is crucial for target relocation, focused imaging and false target suppression [5,6,7,8,9,10,11,12,13,14,15]
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