Towards in-situ calibration of gyro and Doppler navigation sensors for precision underwater vehicle navigation

Addresses a practical problem arising in the calibration of bottom-lock Doppler sonar for the navigation of underwater robot vehicles. Employing a least-squares method, the rotational alignment offset between a bottom-lock Doppler sonar and a north-seeking gyroscope can be experimentally determined using sensors commonly deployed with a vehicle in the field. It requires sensor values from the vehicle's Doppler sonar and 3-axis gyroscope, and absolute vehicle position fixes from a long-baseline or short-baseline acoustic navigation system. The performance of the calibration method is evaluated with simulated Doppler data possessing measurement noise typical of that found in actual in-water vehicle sensor data.

1. Introduction

This paper examines the problem of in-situ calibration of navigation sensor alignment parameters arising in the precision bottom-lock doppler navigation of underwater vehicles. Previously reported studies by the authors and others have shown that the principal error sources arising in the doppler navigation of underwater vehicles are (a) heading and attitude sensor accuracy and precision and (b) sensor rotation calibration (alignment) errors between the doppler sonar and the attitude sensor [5], [19]. Recently, a new class of low-cost, true-north seeking, 3-axis fiber-optic gyro-. scopes have become available [10]. These new optical gyroscopes possess the ability to find true North at sea within about five minutes from a cold start, and provide a rated dynamic accuracy of 0.1°-about an order of magnitude better precision than the best available gyro-stabilized magnetic compasses, and is absolutely referenced to the geode. This new class of gyroscopes effectively solve problem (a), accuracy and precision, and in consequence problem (b), alignment and calibration, becomes the principal error source,