Abstract:
Acoustic synthetic aperture processing (SAP) has been discussed in a special issue of IEEE J. Ocean Eng. [ 17(1) (1992)]. It is noted that SAP essentially converts temporal gain to spatial gain. If one is working in an isotropic noise field and is concerned with the total gain only and not directionality, SAP provides no ``new'' gain. However, in the case of a nonisotropic noise field, one can achieve much larger spatial gain from SAP at the expense of temporal gain. To achieve this larger spatial gain, one needs to maintain the signal and null out the directional noise. A major problem in maintainng the signal in SAP is that the signal can be degraded due to propagation perturbation resulting from multipath interference. To overcome this problem, it is proposed to incorporate matched-field processing (MFP) in SAP. In MFP, a propagation code is used to model the multipath interference and includes it in matched-filtering data. It will reduce multipath signal loss and provide better source localization. To address signal response of the synthetic aperture MFP, data from a 1995 shallow-water experiment were processed and results will be discussed.