The SeaBED AUV
SeaBED's twin-hull design stands in stark contrast to that of most commercial "torpedo-shaped" AUVs, but provides greatly enhanced stability for low-speed photographic surveys. SeaBED is approximately two meters long and weighs nearly two-hundred kilograms. The vehicle has two main pressure housings, containing the electronics and the batteries. The electronics are located in the top hull, and connected to the batteries and sensors in the bottom hull, by wet cabling routed through the vertical struts.
SeaBED is equipped with an RDI Workhorse Navigator ADCP for bottom-locked navigation, an Imagenex Delta-T imaging sonar for bathymetry capture and a custom camera system based on high dynamic range Prosilica cameras. It also has a WHOI MicroModem for acoustic communication and navigation, and a SeaBird CTD sensor for measuring salinity and water temperature. The main computer is a 1.2GHz Pentium processor, running Ubuntu Linux 8.04. The custom vehicle software is primarily written in the C programming language.
The objective of the Seabed AUV is to serve as a readily available and operationally simple tool that allows rapid testing of docking methodologies and imaging algorithms. We expect to actively pursue repeat surveys for change detection and quantification in areas such as: sidescan sonar survey, photomosaicking, 3D image reconstruction from a single camera, image based navigation, and multi-sensor fusion of acoustic and optical data.
Seabed is a hover-capable vehicle that performs optical sensing with a 12bit 1280x1024 monochrome CCD camera. Acoustic high resolution mapping is achieved using an MST 300 kHz sidescan sonar with a swath width of 400m. A Seabird conductivity and temperature sensor, RDI ADCP and Acoustic Modem are also present.
The AUV is designed for operations from small vessels with minimal support equipment. It has an operational depth of 2000 meters and at 1 m/s can run for up to 10 hours and survey 36 km per mission.
Navigation is performed with standard long baseline (LBL) acoustic nets and a Doppler Velocity Log (DVL), which also performs water column current measurements. Update rates are in the order of 5 Hz, allowing closed loop control of position. Depth is measured from a Paroscientific pressure sensor while altitude is obtained from the DVL. A Crossbow AHRS provides heading, pitch and roll readings. Current capabilities allow positioning accuracy on the order of 0.1 meters.