A sensor system for the navigation of an underwater vehicle

A sensor system for an underwater vehicle is described. he vehicle is equip ped with inclinometers, gyroscopes, a magnetometer a pressure gauge, and a sonar system. The sensor models used for the inclinometers and gyroscopes a re straightforward; however the magnetometer can be corrupted by variations in the earth's field caused by: external objects and internal magnetic fie lds. We show how to use inclinometer data to adjust for a limited set of ex ternal field variation. We also show how to calibrate the magnetometer to c ompensate for static and thruster-dependent internal fields. The sonar unit uses range differentials between cheap time-of-flight sonar to follow a ta rget. This reduces signal processing since data association is only require d on target acquisition, and removes the need to scan an entire landscape, which is usually slow. The gyroscopes are fused via a second indirect filte r system. The vehicle attitude is represented as a quaternion; these have a low computational burden. and lack discontinuities and singularities. The simplicity of the indirect filter permits very fast update rates, so that t he system may follow rapid vehicle rotations.