High-resolution swath bathymetry using MIMO sonar system

Abstract

For increasing the cross-track resolution, the multiple input multiple output (MIMO) technique is introduced into the swath bathymetry system and a new swath bathymetry approach using MIMO sonar is proposed. The MIMO sonar is composed of two parallel transmitting uniform linear arrays (ULAs) and a receiving ULA which is perpendicular to the former. The spacing between the two transmitting ULAs is equal to the product of the receiving sensor number and the receiving inter-sensor spacing. Furthermore, two narrowband linear frequency modulation (LFM) pulses, sharing the same frequency band but with opposite modulation slopes, are used as transmitting waveforms of the two transmitting ULAs. With such an array layout and transmitting signals, the MIMO sonar can sound a swath with the cross-track resolution doubling that of the traditional multibeam sonar using a Mills cross array. Numerical examples are provided to verify the effectiveness of the proposed approach.

High‐range‐resolution two‐dimensional imaging using frequency diversity multiple‐input–multiple‐output sonar

“…Afterwards, the M groups of echoes are beamformed individually and processed jointly so as to synthesise an image with high‐range resolutions. This procedure is quite different from the methods in [18, 27–30] where a high‐cross‐range resolution is achieved while the range resolution remains unchanged.…”

“…The far‐field seabed target is modelled as P ideal scatterers. Accordingly, the echo at the n th ( n = 1, 2, …, N ) receiving element, denoted by x n ( t ), can be expressed as the sum of M LFM pulses with different time delays and attenuations [27–30] where σ p denotes the reflectivity of the p th scatterer, denotes the time delay of the m th ( m = 1, 2, …, M ) transmitted pulse from the m th transmitting element to the p th scatterer, denotes the time delay from the p th scatterer to the n th receiving element, and z n ( t ) denotes the additive white Gaussian noise at the n th receiving element.…”

“…As described in [27–30], a matched filter can be considered as a correlator under a low Doppler shift condition, and hence the output of a matched filter can be expressed as the sum of auto‐ and cross‐correlation terms. Since transmitting pulses are independent from the noise and the CCFs are low enough when compared with the ACF peak, (4) can be simplified as the summation of auto‐correlation terms [27–30] where denotes the ACF of the m th LFM pulse.…”

“…Consequently, the transmitting aperture is lost and the cross‐range resolution is only determined by the receiving array. Therefore, the effective aperture of the MIMO sonar is the same as that of the single‐input–multiple‐output (SIMO) Note that the effective aperture here is quite different from those in [18, 27–30] where the full aperture produced by the spatial convolution of transmitting and receiving arrays is available.…”

Hybrid phase shift and shifted sideband beamforming for large‐aperture MIMO sonar imaging

“…In this paper we focus on the MIMO sonar with colocated elements, and without special statement we simply use MIMO sonar for short. Unlike the traditional active sonar using only one kind of waveform during a ping, the MIMO sonar emits orthogonal waveforms via all transmitting elements simultaneously [4][5][6][7][8][9][10][11][12][13][14]. At the receiving end, replicas of transmitted waveforms are utilised to matched filter echoes at each of the receiving element and hence, a great number of virtual elements are produced at the outputs of matched filters [4,5].…”