Correlation-log-based underwater navigation

A navigation system for a launch-and-forget autonomous underwater vehicle (AUV) that can be realized with commercially available components is described. The navigation system will be truly autonomous, requiring only a knowledge of the vehicle´s initial position and attitude. The launch-and-forget requirement is shown to restrict navigation options to either an inertial navigation system or an arrangement using sonar-based two-axis speed-over-the-ground measurements (sonar velocity logging) and a heading reference device. Simple simulation modeling based on component accuracies shows that the sonar velocity logging method is a feasible proposition that will satisfy the navigation requirement. Commercially available sonar velocity logs operate on either a Doppler shift or a correlation principle. The merits of each in their application to the AUV navigation problem are discussed, and it is concluded that the correlation velocity log offers significant advantages over the Doppler log. The accuracy of the correlation log is shown to be less sensitive to mounting alignment errors and to the effects of vehicle pitch and roll