Coral reef habitat-mapping: how much detail can remote sensing provide?

ABSTRACT

The capability of satellite and airborne remote sensing methods for mapping Caribbean coral reefs are evaluated. Reef habitats were categorised into coarse, intermediate and fine detail, using hierarchical classification of field data (percent cover in 1 m quadrats and seagrass standing crop). Habitats were defined as assemblages of benthic macro-organisms and substrata and were mapped using the satellite sensors Landsat MSS, Landsat TM, SPOT XS, SPOT Pan and merged Landsat TM / SPOT Pan. Habitats were also mapped using the high-resolution digital airborne sensor, CASI. To map areas larger than 60 km in any direction, with coarse detail, Landsat TM was the most accurate and cost-effective satellite sensor (SPOT XS when less than 60 km).

For maps with intermediate habitat detail, aerial photography (from a comparable study in Anguilla) exhibited similar accuracy to Landsat TM, SPOT XS, SPOT Pan and merged Landsat TM / SPOT Pan. Landsat MSS was consistently the least accurate sensor. Maps from CASI were significantly (p<0.001) more accurate than satellite sensors and aerial photographs. Maps with detailed habitat information (i.e. >9 reef classes) had a maximum accuracy of 37% when based on satellite imagery, but aerial photography and CASI achieved accuracies of 67% and 81% respectively.

The capability of satellite and airborne remote sensing methods for mapping Caribbean coral reefs is evaluated. Commissioning of new aerial photography does not appear to be a cost-effective option; satellites are cheaper for coarse habitat mapping, and detailed habitat mapping can be conducted more accurately and cheaply with CASI. The results will guide practitioners in matching survey objectives to appropriate remote sensing methods.