Mapping coral reef benthic substrates using hyperspectral space-borne images and spectral libraries

The suitability of Hyperion, the first civilian hyperspectral sensor in space, for mapping coral reef benthic substrates has been investigated in this study. An image of Cairns Reef, in the northern section of the Australian Great Barrier Reef (GBR), was acquired during Hyperion Calibration and Validation activities. A field experiment was carried out on Cairns Reef to collect information about the optical properties of the water in the area and to map benthic cover by means of video transects. An approach was used to classify the Hyperion image that allows convenient mapping of benthic substrate type and water depth simultaneously. A hyperspectral library of radiance at Hyperion altitude was simulated using a spectral library of GBR benthic substrates, a Hydrolight 4.1 radiative transfer model, and an in-house atmospheric model similar to Modtran-3.7. The image was then classified using the Hyperion at-sensor radiance data and the Spectral Angle Mapper metric using the simulated at-sensor spectral library. The results suggest that using spectral libraries created with forward modelling from the sea bottom to top of the atmosphere are useful tools for interpretation of reefs and can give better results in image classification than classifying the image after removing atmospheric and water column effects. The results also suggest that bottom type and water depth can be separated and mapped simultaneously provided hyperspectral data is available.