Primary experimental results of the navigation method of multiple autonomous underwater vehicles

We report the first experimental results of the navigation method of multiple Autonomous Underwater Vehicles (AUVs) for wide seafloor surveys proposed by us in our previous reports. The key idea of the proposed method is that moving AUVs estimate their states (horizontal position and heading angle) based on AUVs remaining stationary on the seafloor (landmark AUVs), alternating between these roles to expand the observational coverage. Moving AUVs land on the seafloor and transmit compressed information about their estimated states to the landmark AUVs when they change the roles. Sea trials were carried out using two AUVs to evaluate the performance of this method. One is the AUV Tri-Dog 1 (TD) which can move and estimate the states and the other is a Dummy AUV (DA) which cannot move but can estimate the states. In the experiments, TD and DA alternatively estimated the states. To evaluate the positioning accuracy of the proposed method, the states were recalculated based on sensor data obtained at sea trials in post processing. As a result, positioning errors of the proposed method were estimated to be smaller than dead reckoning. The Errors were found to be about 0.4 m in horizontal position and about 1.5 degree in heading angle. The method demonstrated to be successful in stable positioning with AUVs alternating between the moving role and the landmark role. Future works include the verification of the method using two AUVs in sea environment to realize wide seafloor survey.