Improved navigation system for USBL users

It is typical for underwater contractors to use an ultra-short baseline (USBL) acoustic navigation system referenced to a precise surface navigation system such as DGPS in order to position a remote vehicle or towbody in shallow to moderate depths. Due, in good part, to the influence of the physical environment, this position data is often very noisy with experienced accuracy being /spl plusmn/50 to 75 meters. Meridian Sciences, a U.S. Navy contractor specializing in navigation refinement, is currently developing a technique which will reduce errors of this magnitude to an error of /spl plusmn/15 meters. As this technique models the inherent errors in all of the system sensors, this improved accuracy will depend on the type and number of sensors used.