TOWFISH ORIENTATION AND POSITION ESTIMATION

A side-scan sonar is' used to detect objects on the sea bottom. The sonar is mounted on a towfish which is connected by tow-cable to a towing ship. The accuracy with which the coordinates of an object can be determined depends heavily on the accuracy of the estimates of the position and orientation of the towfish. In this paper we deal only with the towfish location and orientation problems. These two problems are treated separately. Data which locates towfish relative to the ship is usually deteriorate by multipath receptions and other effects. In order to overcome the serious degradation existent in the location measurements, a modified Kalman filter is proposed. An estimate of the state transition matrix for this filter is derived, and a means of switching between two Kalman gains is suggested. The feasibility of the proposed filter is justified by a case study. In addition, improved estimates of towfish pitch and heading measurements are obtained by a separate system employing model identification and subsequent Kalman filtering. Application of these methods to data from similar towed side-scan sonar systems should yield significant gains in object location accuracy.