Using an Acoustic Ground Discrimination System to map coral reef benthic classes

Abstract

An Acoustic Ground Discrimination System (AGDS) can extract information on the nature of the seabed. Compared to satellite or airborne sensors, AGDS is rarely used in tropical environments but is easy to operate and produces a modest amount of digital data. This study aimed to assess acoustic surveys of coral reef benthic classes using a RoxAnn @ AGDS in the Philippines. Benthic classes were categorised into four levels of detail using hierarchical classification of field data. Using independent data, subsequent maps were shown to have overall accuracies of: 85% at coarse resolution (three classes), 61% and 54% at two intermediate levels (five and four classes) and 28% at fine resolution (10 classes). These accuracies are assumed to be conservative because of constraints during this study including semi-quantitative data for discriminating class types, benthic changes between AGDS and accuracy assessment surveys and lack of differential global positioning system (GPS). Despite these limitations, AGDS accuracy levels were comparable to those achieved by satellites and it has advantages including greater water penetration and independence from cloud cover. Acoustic data are, therefore, proposed as useful tools for tropical habitat mapping and complementary to satellite and airborne sensors.