Abstract:

Experimental and analytical studies have clearly shown the feasibility and applicability of passive and active synthetic aperture sonars (SAS). These investigations have spanned the infrasonic to ultrasonic frequency range. However, passive SAS has not gained widespread use due to three arguments. The first is based on a single hydrophone system, and knowledge of the source frequency is required for bearing estimation. However, with multiple hydrophones, both the bearing and frequency can be estimated simultaneously. The second argument claimed that there was no ``new gain,'' since the number of spatial and temporal degrees of freedom are constant. However, this analysis failed to account explicitly for the movement of the array, thereby ignoring the Doppler information. The third argument claimed that temporal coherence time must be at least equal to the time of synthesization. This argument ignores the applicability of sequential coherence corrections. This paper will clarify and place these arguments in perspective. Experimental results and analyses showing the performance improvements will be presented.