Model-Based Processing for a Short Towed Array

Model-based signal processing techniques for a short towed array are experimentally demonstrated for both broad band and narrow-band signals. It is shown that accurate bearing and horizontal wavenumber estimations, for frequencies ranging from 220 Hz to 1228 Hz, can be made for acoustic apertures as short as 0.5 wavelength. The data were the result of an experiment carried out in Nantucket sound, where an autonomous underwater vehicle towed a hydrophone array for the purpose of forming a long synthetic aperture. The AUV towed the array outward from a fixed narrow-band source on a straight radial track out to 4 km. Processing of the signal over the entire 4 km synthetic aperture, based on a normal-mode propagation mode, allowed for characterization of the channel. During the experiment a ferry passed through the area. This "target of opportunity" provided a basis for testing model-based passive synthetic aperture bearing estimation routines.