AND HIGH-RESOLUTION TIME DELAY ESTIMATION

One of the difficult sonar signal processing problems has been the case where the acoustic FM signal is embedded in reverberation noise, due to the presence of multipath and observation noise. The effects of multipath propagation have been shown to introduce biases and high variances in the bearing and range estimation of acoustic sources. It is therefore very critical to take into account multipath propagation in the time delay estimation problem and minimize or eliminate its effect. The impulse response of the multipath underwater connnunication channel is generally nonminimum phase and consists of the time delays and their attenuation constants. The specific problem we address in this paper is the one where the time delays are closely-spaced, i .e., the distance between two consecutive time delays is significantly less than the duration of the a utocorrelation of the FM signal. We introduce in this paper a new highresolution estimation method using the cumulant cepstra (polycepstra) of the received s ensor data as the basic tool for reconstruction. The effectiveness of the method is demonstrated for different noise conditions and lengths of data.