Sonar waveform design for optimum target detection: The impact of object burial state

The design of transmit waveforms in sonar and radar that optimize the probability of detection of a known target is an area of active interest. Previous research has demonstrated the benefits of optimal transmit waveforms for enhanced target detection, versus the transmission of more conventional waveforms such as broadband LFM pulses. For maximum benefit, the scattering function or frequency response of the target to be detected must be known, along with the spectral or statistical properties of the environment. In this paper, we examine the impact of a mismatch between the expected frequency response of the target, for which the optimal transmit waveform was designed, and the actual frequency response of the target. In particular, we design the optimal sonar transmit waveform based on the free-field response of the target, and then examine the effects on detection performance of burial of the target in sediment. Simulations of the sonar backscatter from a steel sphere in the water column and at various stages of burial demonstrate that the impact of mismatch becomes increasingly detrimental as the target becomes increasingly buried. For fully buried targets, the impact is such that transmitting a simple broadband LFM pulse can yield improved detection relative to “optimal” waveform design wherein there is a mismatch between the expected (free-field) and actual (buried) frequency response of the target.