Toward wide seafloor surveys using multiple autonomous underwater vehicles

In this paper, we report experimental results of the navigation method of multiple Autonomous Underwater Vehicles (AUVs) for wide seafloor surveys, which we had proposed in the previous reports. Moving AUVs estimate their states (horizontal position and heading angle) based on AUVs remaining stationary on the seafloor (landmark AUVs). Moving AUVs land on the seafloor and transmit their information about the estimated states to landmark AUVs after completing tasks around landmark AUVs. This information is derived from "particle clustering" to reduce the required communication data size because typical data rates of acoustic communications in underwater environments are too small to transmit the large information within a reasonable time period. In order to verify the performance of this method, sea trials were carried out using the AUV Tri-Dog1 (TD) and a Dummy AUV (DA). TD successfully navigated around DA. TD and DA alternatively estimated the states using the information of the states transmitted by the other vehicle. TD and DA also mutually controlled the navigation role, the moving role and the landmark role by acoustic communication. As a result, TD and DA alternated the roles 10 times while sharing the information of the states estimated by the other vehicle. Standard deviations of the states were found to be suppressed to be about 0.2 m in the horizontal position and about 1.0 deg in the heading angle. Positioning errors were estimated to be about 0.5 m in X direction, 0.8 m in Y direction, and 2.5 deg in heading angle after 90 minute navigation. Therefore the method was successful in stable positioning while alternating between the moving role and the landmark role. Future works include the verification of the method using two AUVs in sea environment.