Pacific Coastal & Marine Science Center
USGS Pacific Coral Reefs Website
Using a diver-towed GPS allows underwater video footage to be georeferenced.
Underwater video footage is being used for independent mapping, and to help ground truth remotely-sensed data. In water depths less than 25 m (80 ft), divers on standard scuba work in teams of three. A GPS (Global Positioning System receiver) location is taken at water entry and exit locations, and divers navigate on a pre-determined course. Alternatively, a GPS unit is towed on the surface by the divers. The videographer uses a digital camcorder in an underwater housing, a geologist takes sediment samples and records notes on the geomorphology of the reef, and a biologist records notes on the biota, zonation, and general health of the coral. Digital video editing software is used in the lab to review the tapes, make annotations, and produce still images for maps and publications.
Mapping in water depths greater than 25 m (80 ft) is accomplished using a boat-towed underwater video mapping system with a depth sensor and an onboard geo-referenced data-logger. This system uses specially written software which translates the signal from the GPS receiver and embeds latitude and longitude directly onto the audio track of a digital video camera. The geo-referenced survey lines, depth and image data are entered into an Geographic Information System (GIS) database. This method provides a cost-effective survey technique for mapping underwater environments, and may be used independently or in conjunction with other survey methods.
Example of mapping with underwater video footage in a Geographic Information System (GIS) database.