The MBARI Low-Altitude Survey System for 1-cm-Scale Seafloor Surveys in the Deep Ocean

The Monterey Bay Aquarium Research Institute has developed a low-altitude survey system (LASS) to conduct cm-scale seafloor surveys of complex terrain in the deep ocean. The LASS is integrated with a remotely operated vehicle (ROV), which is operated at a 3-m standoff to obtain 5-cm-lateral-resolution bathymetry using a multibeam sonar, 1-cm-resolution bathymetry using a wide-swath lidar laser scanner, and 2-mm/pixel resolution color photography using stereo still cameras illuminated by strobes. Surveys are typically conducted with 3-m line spacing and 0.2-m/s speed and executed autonomously by the ROV. The instrument frame actively rotates to keep the sensors oriented normal to the seafloor. The strobe lights, mounted on swing arms on either side of the ROV, similarly rotate to face the seafloor. Areas of 120 m × 120 m can be covered in about 8 h. Example surveys include 1) deep-sea soft coral and sponge communities from Sur Ridge, offshore Central California; 2) a warm venting site hosting thousands of brooding octopus near Davidson Seamount, also offshore Central California; and 3) a high-temperature hydrothermal vent field on Axial Seamount, on the Juan de Fuca Ridge. An advantage of combining optical and acoustic remote sensing is that the lidar and cameras map soft animals, while the multibeam sonar maps the solid seafloor. The long-term goal is to field these sensors from a hover-capable autonomous platform rather than ROVs, enabling efficient 1-cm-scale seafloor surveys in the deep ocean.