Arrival time variations of pulses in shallow water and low frequency acoustical underwater positioning
Boris Katsnelson, and Mohsen Badiey

         Variations in acoustic arrival time in shallow water are presented to establish a method for long range underwater acoustical positioning systems (UWPSs) with possible applications for underwater vehicles. At the present time, there are different methods used for UWPS for only short distances (about a few hundred meters), relating the sound signals to distance based on ocean physical properties. It is possible to use arrival times of high-frequency signals (up to 100 kHz) radiated by a set of reference sound sources (such as 3-4), placed at different points in an area to determine the position. However, the main problem for long range positioning (i.e., operation area of several hundred to thousand kilometers) is significant spatial and temporal variabilities of waveguide environmental properties affecting the signal travel time. To establish limits for low-frequency acoustical UWPS, here we use recent field observations in the SW06 experiment to estimate signal arrival time variations caused by different hydrodynamic conditions observed simultaneously during acoustic transmissions. Based on preliminary mapping of the operation area, and the subsequent optimization, the accuracy related to the waveguide dynamics is presented.

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