Passive localization using a spatially-referenced towed array

We extend our work on the location estimation error performance of towed line array configurations of uniformly spaced passive hydrophones with emphasis on the spatially-referenced towed array (SPARTA). Using Cramer-Rao lower bound (CRLB) analysis as the means to compare the potential performance of different array configurations with spherical wavefront arrivals, we have previously shown that the variance of location estimates can be slightly improved for small observation times if a SPARTA is used instead of a conventional towed array (CTA) when the frequency of a fixed-position source is unknown. In this paper, the relationship between spherical wave location estimation CRLBs and plane wave bearing estimation CRLBs is shown, the realization of the CRLB by the maximum likelihood (ML) method is revisited, and the performance of towed arrays over longer observation times is considered. The combination of all these results helps to determine under what conditions the SPARTA can provide the potential for improved source localization