Thematic mapping of reefs by processing of simulated SPOT satellite data: application to the Trochus niloticus biotope on Tetembia Reef (New Caledonia)

Abstract

Evploitat~on of trochus Trochus nlloocus is important for Pac~fic islanders The shell yields valuable mother-of-pearl of w h ~ c h 2000 tons were exported from New Calcdonia in 1978 Knowledge of the exploitable stock requires a good estlmate of the surface area occupied by this gastropod which colonises dead coral reefs Because trochus environments In New Caledonia are very extensive and access is difficult, synoptic methods of estimation are called for High resolution remote sensing appears to be a particularly suitable method Slmulat~on of images to be obtained from the French SPOT satellite was carried out in New Calcdonia in December 1983 This paper deals with the method used to process the d~gital high resoluhon images that will be produced by SPOT Results are presented as thematic maps of the main reef environment types, with their respective surface areas Among hard reef bottom covers, the trochus env~ronment was finely analysed and areas identified were compared w t h ground truth observahons and w t h aenal photograph interpretation The potential usefulness of high resoluhon SPOT images is conf~rmed for thematic mapplng and evaluat~on of shallow-livlng reef resources