Spectral reflectance of coral reef benthos and substrate assemblages on Heron Reef, Australia

Abstract

Studies investigating the spectral reflectance of coral reef benthos and substrates have focused on the measurement of pure endmembers, where the entire field of view (FOV) of a spectrometer is focused on a single benthos or substrate type. At the spatial scales of the current satellite sensors, the heterogeneity of coral reefs even at a sub-metre scale means that many individual image pixels will be made up of a mixture of benthos and substrate types. If pure endmember spectra are used as training data for image classification, there is a spatial discrepancy, because many pixels will have a mixed endmember spectral reflectance signature. This study investigated the spectral reflectance of coral reef benthos and substrates at a spatial scale directly linked to the pixel size of high spatial resolution imaging systems, by incorporating multiple benthos and substrate types into the spectrometer FOV in situ. A total of 334 spectral reflectance signatures were measured of 19 assemblages of the coral reef benthos and substrate types. The spectra were analysed for separability using first derivative values, and a discrimination decision tree was designed to identify the assemblages. Using the decision tree, it was possible to identify 15 assemblages with a mean overall classification accuracy of 62.6%.

Acknowledgements

Sincere thanks to Jeremy Bourgoin, Chris Roelfsema, Julie Scopelitis, Karen Brady, Robert Canto and the staff at Heron Island Research Station for assisting with data collection on Heron Reef. Chris Roelfsema also provided valuable feedback on an earlier manuscript draft. This project was supported by a CSIRO Land and Water Flagship Postgraduate Scholarship to I. Leiper, the Centre for Spatial Environmental Research and an Australian Research Council Discovery Grant to S. Phinn and P. Mumby (DP0663). Thanks to the two anonymous reviewers for their feedback, which strengthened the manuscript.