| Peter J. Mumby | |
| Edmund P. Green | |
| Christopher D. Clark | |
| Alasdair J. Edwards |
The digital airborne sensor, CASI (Compact Airborne Spectrographic Imager) has considerable potential for mapping reef habitats. Here we present an account of one of the first coral reef applications.
The CASI was flown over reefs of the Turks and Caicos Islands (British West Indies) and set to view 1 m pixels in 8 spectral bands. In addition, reef habitats were sampled in situ by visual assessment of percent cover in 1 m quadrats. Seagrass standing crop was assessed using a calibrated visual scale. Benthic habitats were classified using hierarchical cluster and Similarity Percentage analyses of the field survey data. Two levels of habitat discrimination were assessed: a coarse level (corals, algae, sand, seagrass) and a fine level which included nine reef habitats.
Overall accuracies of CASI-derived habitat maps were 89% and 81% for coarse and fine levels of habitat discrimination respectively. Accuracies were greatest once CASI data had been processed to compensate for variations in depth and edited to take account of generic patterns of reef distribution. These accuracies were significantly (p<0.001) better than those obtained from satellite imagery of the same site (Landsat MSS, Landsat TM, SPOT XS, SPOT Pan, merged Landsat TM / SPOT Pan).
Results from CASI were also found to be significantly better than those from 1:10 000 colour aerial photographs from a study in Anguilla (Sheppard et al., 1995). However, the studies may not have been entirely comparable due to disparity in the areas mapped by each.