3D autonomous underwater navigation using seabed acoustic sensing

Autonomous Underwater Vehicle (AUV) being a powerful tool for exploring and investigating ocean resources can be used in a large variety of oceanographic, industry and defense applications. Underwater navigation for AUV is still a challenging task and is one of the fundamental elements in modern robotics because the ability of AUV to correctly understand its position and attitude within the underwater environment is determinant for the success in the different applications. AUV navigation usually is based only on information obtained from Doppler Velocity Loggers, Inertial Navigation Systems, etc. due to the absence of an external reference sources. But this type of navigation is subjected to a continuously growing error due to the absence of the absolute position measurement (for example, received from GPS or GLONASS) which is typical for the majority of UAV applications. These measurements might be provided by observation of so-called feature points like in Unmanned Aerial Vehicles (UAV) case, but the big difference between acoustical and optical images makes it a rather difficult problem which solution needs detailed preliminary mapping of the operational seabed area. The new generation of acoustic imaging gives rise to the new approaches to AUV navigation based on the absolute velocity measurements. By analogy with the optical flow approach coming from the area of UAV the evolution of the seabed map produces the information related to the absolute motion of the AUV. The principal advantage of the proposed algorithm is that the fusion of the acoustic mapping and the Inertial Navigation System (INS) gives the absolute velocity of the vehicle with respect to the seabed. In some sense the suggested algorithm operates as multibeam Doppler Velocity Log (DVL), though in different way and in different environment. Even in the theory the DVL operates perfectly over the flat surface, but the suggested algorithm needs the presence of the relief and uses the evolution of the relief range obtained by sonar and measured from the ship to the seabed as a source of own speed.