Performance and limitations of acoustic positioning using a tetrahedral ultra-short baseline array and an acoustic modem source transmitting frequency-hopped sequences

The operation of unmanned underwater vehicles requires communications with other nearby vehicles as well as accurate positioning to prevent duplication of work, collisions and other mishaps. This thesis details the integration of an ultra-short baseline positioning system with four transducers arranged as a tetrahedron for use with the FAU Dual Purpose Acoustic Modem. The source position is estimated by processing coherently a series of frequency-hopped pulses to obtain a set of bearings, optimally combined through maximum likelihood estimation of the azimuth and elevation. A simulation has been implemented and experiments have been performed in a calibration tank. Model and experiments confirm that the accuracy of this system improves with the number of pulses and the signal-to-noise ratio. A mean positional error of 5.51% can be obtained with an SNR of 20 dB and a single processed pulse, the error decreases to 2.84% using six processed pulses.