Decreasing transponder dependence

Many efforts in navigation research and development seek to reduce (or eliminate) the role of seafloor moored transponders in a navigation solution. As discussed above, LBL transponders provide an absolute reference, but this comes at a high cost. Transponders are deployed and surveyed from the surface in preparation for AUV missions and then recovered after completion of the mission. This evolution erodes operational efficiency, requiring hours or even days to complete depending on the environment and the mission. Such a seafloor-based external reference also limits the range of an AUV; typical transponder networks can only cover a few square kilometres.

Work has been done to eliminate the survey step in deploying transponders. One solution is to place the transponders at the surface, on floating buoys, where GPS can provide constant position updates. This has been used for tracking (the position is recorded at the surface, but not available subsea in real-time) AUVs for survey operations (Desset, Damus, Morash, & Bechaz, 2003). Another approach is to concurrently localize the fixed transponders while navigating using the range information. Using concurrent localization and mapping (CML), also known as simultaneous localization and mapping (SLAM), researchers have created a consistent map of the environment using only range information when the transponder locations are not known before the mission (Olson, Leonard, & Teller, 2006). Yet another approach is to have the AUV actually deploy the fixed transponders. This solution addresses a military need to limit the detection for AUV operations.

Instead of reducing the time spent on survey, another possible method is to decrease the number of transponders necessary to provide an absolute reference. Initial research efforts were focused on proving the theory of single beacon navigation (Larsen M. B., 2000). More recently this effort has moved from theoretical research to practical implementation, including algorithm development and integration into operational platforms such as the REMUS AUV (Hartsfield, 2005).

The incorporation of reliable acoustic communication has provided additional opportunity solutions to decrease the dependence on acoustic transponders. With the ability to transmit ephemeris data from a surface ship to the submerged platform, it becomes possible to eliminate the transponders all together and use the moving surface ship (with GPS navigation)

as fixed reference (Eustice, Whitcomb, Singh, & Grund, 2007). The Hugin AUV, a successful commercial survey tool, has used a similar technique to provide position updates and change the AUV mission from the surface (Vestgard, Storkersen, & Sortland, 1999)

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