Abstract for presentation at The 13th Australasian Remote Sensing and Photogrammetry Conference

Validation of benthic habitat maps produced from remote sensing imagery is quite time consuming and expensive. Validating maps of seagrass biomass is even more sophisticated and time consuming, as seagrass samples have to be collected from imaged area and then dried and weighted in laboratory. The number of sampling points that can be collected this way is limited. A photo transect method for benthic validation was developed in Centre for Remote sensing & Spatial Information in University of Queensland where the bottom types are identified based on still images taken along 100 m tape geolocated and fixed to the seafloor. We developed this method further to be able to estimate seagrass dry weight along the photo transects. For that purpose we selected study areas from almost bare sand to dense seagrass on sandy bottom and to seagrass beds with dens macroalgal or coral cover. Photo of each bottom class was taken before collecting algae and seagrasses from 25x25 cm quadrates. Dry weigh of seagrasses (and macroalgae, if present) from each quadrate was measured in laboratory. Seagrass biomass along the photo transects can then be estimated by visually comparing the transect photos with photo library of quadrates with known seagrass biomass. This allows getting geolocated seagrass biomass estimates for relatively large areas with limited amount of laboratory work. The photo-library method was used to create seagrass biomass maps of Ngederrak Reef, Palau, from QuickBird and Hyperion imagery.