Centimeter scale seafloor relief measurement using an ROV

Abstract

For high-frequency acoustic backscatter modeling, in the band 1 to 100 kHz, centimeter scale seafloor roughness is an important parameter. A measurement method was devised for deployment aboard a remotely operated vehicle (ROV) consisting of lasers and a video camera. It was designed to measure small-scale roughness in the range of spatial wavelengths from 0.01 to 1 m. The ROV is well suited to this application because it can hover above the seabed, and it can cover a relatively large area. A cylindrical lens was used to spread the laser beam from a low-power laser into a fan, and direct it downward to produce a stripe on the sediment. Viewing from an oblique angle with a video camera, the profile of the sediment directly under the stripe was obtained. The most difficult problem was precisely determining and tracking the position of the ROV. In the SAX99 experiment, positioning was achieved by using small shells and other objects on the seafloor as landmarks. [Work supported by ONR, Ocean Acoustics.]