High-resolution repeat bathymetric mapping using a mid-size autonomous underwater vehicle

Shipborne bathymetric surveys south of Santa Barbara, CA indicate that massive slope failures have occurred along the northern flank of the Santa Barbara Basin. This region is seismically active and has the highest sedimentation rates along the California coast due to rapid erosion of the Transverse Ranges. A set of geodetic monitoring systems is being developed to study the character and deformation of the ocean bottom in this region, particularly that of a prominent east-west trending crack aligned with the head scarp of one of the underwater landslides. One component is a high-resolution repeat bathymetric mapping system composed of a multibeam sonar mounted inside a Bluefin 21 AUV. Navigation to the decimeter level is provided by an inertial navigation system and accurate depth sensor, and by a long baseline (LBL) acoustic transponder system previously developed to monitor tectonic plate motions. The quality of the data, particularly that from the high-precision LBL system, is enhanced significantly by the decrease in the radiated acoustic and vibration noise of the AUV to levels at, or below, ocean background noise levels through modifications to the AUV propulsion system. [Work sponsored by British Petroleum and the Office of Naval Research.]