Optical Validation

Except for very small areas, it is not logistically feasible to optically image more than a small fraction of the seafloor deeper than about 30 m within a coral reef ecosystem using any technology currently available. Accordingly, optical imagery of the seafloor is collected primarily to ground truth or validate the interpretation of benthic habitat characteristics from bathymetry, backscatter imagery, or other data. To date, optical data have been collected using two different types of systems. In shallow waters, at depths between a few meters and 20?30 m, towboard divers with the NOAA Pacific Islands Fisheries Science Center?s Coral Reef Ecosystem Division (CRED) collect video or still imagery while being towed behind a small boat over track lines pre-programmed into a handheld GPS unit. However, the majority of seafloor in most Pacific coral reef ecosystems is deeper than the approximately 30 m maximum depth attainable by standard CRED towboarding methods. For these deeper areas an evolving series of underwater camera sleds, usually referred to as the Towed Optical Assessment Device (TOAD), have been used to acquire optical validation data.

These data provide optical observations that will be correlated with bathymetry and acoustic backscatter imagery to develop benthic habitat maps for selected US locations in the Pacific.