1. In an echo-location system, a method for adaptively estimating the target reflectivity sequence from received data that has been corrupted by non-Gaussian disturbances, said method comprising: estimating the statistics of the prevailing non-Gaussian disturbance in the received data; generating an approximate likelihood function from the estimated statistics of the prevailing non-Gaussian disturbances; and maximizing the likelihood function by applying an iterative gradient-descent algorithm to obtain the target reflectivity sequence.