Synthetic aperture processing for a towed array and a moving source

In this paper the use of synthetic aperture processing is examined for simultaneously estimating a source’s unknown rest frequency, relative radial speed, and bearing from towed array hydrophone data. By examining this three-dimensional estimation problem, it is concluded that for the situation where the velocity and/or rest frequency of the source are unknown there is no advantage in using coherent synthetic aperture techniques instead of incoherent methods to estimate the source’s bearing. The case of multiple sources is also examined and it is concluded that although long-time coherent processing can improve bearing resolution for two closely spaced targets, the same results can be obtained by taking a long-time Fourier transform and then using conventional beamforming methods.