Performance of maximum likelihood estimation for multipath TDOA passive ranging

This paper presents an estimation procedure for exploiting multipath signal propagation in shallow water to perform passive ranging. The scenario of interest is a pair of sensors receiving an underwater acoustic signal that has arrived via a bounce from the ocean floor. This approach also applies in other situations, for example, to multiple airborne sensors passively receiving emissions from an airborne source with signal bounce off the earth's surface. We develop an implicitly-defined maximum likelihood estimator; provide a numerical scheme for calculating the estimate; and derive expressions for the estimator bias and variance. Finally, we show that at low noise, the bias is negligible and the variance is equivalent to the usual Cramer-Rao bound on unbiased estimators.