Exploitation of Trochus niloticus is important for Pacific islanders. The shell yields valuable mother of pearl of wich 2.000 tons were exported from New Caledonia in 1978. Knowledge of the exploitable stock requires a good estimate 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. Simulation of images to be obtained from the French SPOT satellite was carried out in New Caledonia in decemlber 1983. This paper deals with the method used to process the digital high resolution 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 environment was finely analysed and areas identified were compared with ground truth observations and with areial photograph interpretation. The potential usefulness of high resolution SPOT images is confirmed for thematic mapping and evaluation of shallow living reef resources.