14. Validation

Adequate understanding of the validity of information contained in coral reef remote sensing products is required to support research and management decisions. This chapter introduces accuracy measures commonly applied to two types of coral related maps: discrete (e.g., benthic cover type) and continuous (e.g., percent coral cover). A critical review of 80 coral reef remote sensing mapping publications presents the approaches and metrics commonly used to measure accuracy. The literature review shows that few studies report accuracy information at all, and when obtained, ‘overall accuracy’ was the most commonly used accuracy measure. Variations in accuracy levels were not only a result of actual differences in map accuracy, but are likely also due to: spatial complexity of benthic features present in the study area; distribution of the calibration and validation samples relative to each other; and the level of detail measured for each sample. As a result, accuracy measures from different studies should be compared with caution and with due attention to how the measures were derived. This chapter enables scientist and managers to understand, design and interpret validation procedures for image-based maps of coral reef environments.