Navigation Strategies of a Cruising AUV for Near-Bottom Survey of a Steep Terrain

Strategies of AUV navigation for achieving the near-bottom survey of a steep terrain are addressed. Unlike a flat terrain, a steep terrain can disrupt an altitude-based bottom-following dive of a cruising AUV. During its near-bottom dive over a steep terrain, a cruising AUV possibly experience longitudinal motion instability accompanied by severely fluctuating heave and pitch which may lead to bottom collision of the vehicle. Based on dive simulations, it is shown that the lost bottom lock of a sonar altimeter and the altitude overestimation are two major sources of the longitudinal motion instability. Underwater acoustic physics interacting with the sea water and bottom, as well as the coupled 3-d.o.f. longitudinal vehicle dynamics are incorporated into our simulation model. As alternative strategies for pursuing more reliable AUV-based near-bottom survey, the slope-following navigation and the pseudo bottom-following navigation have been investigated.