Estimating inertial position and current in the midwater

This paper describes a method for fusing an inertial position measurement from an Ultra-Short Baseline (USBL) sonar with a water-relative velocity measurement (from DVL, ACM, or other device) to improve knowledge of an underwater vehicle´s inertial position. The goal is accuracy sufficient to enable closed-loop position control in the midwater. In this paper we describe the implementation of a kinematic estimator which computes vehicle inertial position and water current velocity. We present the details of this estimator as well as results of field trials which demonstrate the viability of the technique. Field experiments show improvements in accuracy on the order of a factor of 5 above the USBL´s raw measurements.