Abstract
When the multi-receiver synthetic aperture sonar (SAS) works with a wide-bandwidth signal, the performance of the range-Doppler (R-D) algorithm is seriously affected by two approximation errors, i.e., point target reference spectrum (PTRS) error and residual quadratic coupling error. The former is generated by approximating the PTRS with the second-order term in terms of the instantaneous frequency. The latter is caused by neglecting the cross-track variance of secondary range compression (SRC). In order to improve the imaging performance in the case of wide-bandwidth signals, an improved R-D algorithm is proposed in this paper. With our method, the multi-receiver SAS data is first preprocessed based on the phase center approximation (PCA) method, and the monostatic equivalent data are obtained. Then several sub-blocks are generated in the cross-track dimension. Within each sub-block, the PTRS error and residual quadratic coupling error based on the center range of each sub-block are compensated. After this operation, all sub-blocks are coerced into a new signal, which is free of both approximation errors. Consequently, this new data is used as the input of the traditional R-D algorithm. The processing results of simulated data and real data show that the traditional R-D algorithm is just suitable for an SAS system with a narrow-bandwidth signal. The imaging performance would be seriously distorted when it is applied to an SAS system with a wide-bandwidth signal. Based on the presented method, the SAS data in both cases can be well processed. The imaging performance of the presented method is nearly identical to that of the back-projection (BP) algorithm.
Highlights
Originating from synthetic aperture radar (SAR) [1,2,3,4,5,6,7,8,9,10], synthetic aperture sonar (SAS) [11,12,13,14,15,16] attracts investigators’ interests due to its high resolution in the underwater field
Considering the traditional monostatic SAS system, the maximum imaged swath is determined by the pulse repetition frequency (PRF), and the low PRF allows for a wide swath
To fairly compare the imaging performance, the only difference of SAS parameters between narrow and wide bandwidth cases lies in the signal bandwidth
Summary
Originating from synthetic aperture radar (SAR) [1,2,3,4,5,6,7,8,9,10], synthetic aperture sonar (SAS) [11,12,13,14,15,16] attracts investigators’ interests due to its high resolution in the underwater field. The sampling of the along-track signal is conducted by this PRF. When a too low PRF is exploited, there would be ambiguous targets in the SAS image as the along-track sampling with this low PFR does not satisfy the Nyquist-Shannon theorem [23]. The SAS system parameters are subject to a trade-off, as the along-track resolution is only improved at the cost of a decreased swath or vice versa. One of the promising systems is the multi-receiver SAS, which employs a single transmitting element and a receiver array. This system can successfully overcome the limitations of Remote Sens.
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