Virtual beams from an FFT beamformer and their use to assess the quality of a towed-array system

Linear towed arrays with sophisticated signal processing systems have become popular for passive sonar and seismic prospecting. This is due to the ease of mobility and the large spatial gains achievable. However, because these systems are mechanically and electronically complex and not constrained to remain linear, the potential for degraded performance is a constant problem. An onboard data-processing system has been developed to assess the performance of towed-array systems. This paper discusses an extension to that system in which the beams steered beyond endfire (virtual beams) can be used to determine the sidelobe suppression capability and self-noise of the sonar and to flag system degradation. This is illustrated by examples from recent ambient-noise measurement exercises.