3D forward looking sonar technology for surface ships and AUV: Example of design and bathymetry application

Abstract

Most modern bathymetry systems are using down-looking multi-beam echo-sounders or side-looking sonars with interferometry technology. At the same time a variety of forward-looking sonars (FLS) provides collision-avoidance information and images of the sea floor ahead of vehicle. The example of sonar considered in this paper realizes a combination of all these important functions: forward-looking bathymetry, collision avoidance and imaging (FLBS). The design under consideration includes three linear receiver arrays and one cylindrical transmitter array that illuminates a wide sector ahead of vehicle. Three receiver arrays provide simultaneously range, azimuth and elevation information and as a result it is possible to generate a large number of soundings in each ping. After correction of artifacts caused by motions and vehicle movement, bottom features and seabed topology are extracted using dedicated processes; the resulting soundings are then integrated in a final map. The backscattered signal intensity associated with each sounding is integrated into a mosaic image of the seabed. The specifics of sonar hardware design, processing algorithms and results of field tests are presented in this paper. The FLBS concept operates at high-frequency to provide directivity in a small form-factor; receive and transmit antennas provide a comparatively narrow beam of around 20° in the vertical plane to avoid multiple echoes phenomenon. The small dimensions of the transducer assembly and electronic bottle could allow such a system to fit into the front payload of a modern mid-size AUV.