Maximum likelihood estimates of a spread-spectrum source position using a tetrahedral ultra-short baseline array

An ultra-short baseline acoustic positioning system has been made compatible with the FAU Dual Purpose Acoustic Modem network to provide azimuth and elevation of modem-type sources. The acoustic antenna is composed of four transducers arranged as a tetrahedron. The position estimation is performed using the detection sequence of each message transmitted by the modem source. This spread-spectrum detection sequence is a series of frequency-hopped pulses. The estimation technique is based on the maximum-likelihood estimation technique originally described by Quazi and Lerro. A simulation has been implemented and experiments have been performed in a calibration tank specifically built for this purpose. Model and experiments confirm that the accuracy of this system improves with the number of pulses and the signal-to-noise ratio, and that a high positioning accuracy can be achieved using the proposed method. This work is sponsored in part by the Office of Naval Research, Code # ONR 321OM, Dr. Tom Swean.