Abstract
We introduce a method aiming to allow small torpedo shaped under-actuated autonomous underwater vehicles achieving seabed following. The constraints of such vehicles concern principally its maximal pitching angle and its turning circle. We present a global seabed following method, which respects these constraints. Path planning is achieved by considering the position of the vehicle in an a priori well-known environment. However, this is not always possible and we propose also a local method adapted from the global one. In this case, the vehicle navigates in an unknown environment, which features he discovers progressively. Two mono-beam sounders situated in the front part of the vehicle provide bathymetric data, which are necessary to plan paths. We explain the reasons of this technical choice and study the model of the acoustic beams. A third sounder allows the detection of underwater cliffs. Then an algorithm based on three specific parts of the sounder's beam is used to characterise the acoustic echoes. Then the path of the vehicle is adapted so as it safely avoids the cliff and goes on following seabed. Finally, we present not only the results obtained during hydrodynamic simulations of the vehicle's movements but also those obtained during experimentations, which have been conducted with Taipan AUV.