Results

The dramatic bleaching events on the coral reefs of the world have once again put a focus on the environment and the necessity for resource monitoring. Sparse point observations from the field can not alone satisfy the need for large scale bleaching status, particularly in remote areas. This paper investigates the value of present high resolution satellites to detect coral bleaching. An image from the Indian Remote Sensing satellite (IRS) from the beginning of the bleaching event in Belize 1998 has been compared to Landsat TM images before the bleaching. The digital counts on the TM scenes have been normalized to the IRS and difference images created. Lighter pixels in areas interpreted as coral habitats were marked and then compared to field observations collected during and immediately after the bleaching event. Several of the lighter pixels in the 1998 image correspond to field observations of bleaching. The spectral characteristics of those pixels have been analysed and methods for an automated analysis suggested. Field observations from Belize suggest that recovery from the 1998 bleaching was variable with both depth and location and that different coral species were differentially affected. The current spatial, spectral and temporal resolution of satellite images limit the ability to detect finer scale bleaching patterns, but methods have been developed to use Landsat, SPOT, IRS etc. for detection of massive coral bleaching. Improved radiometry of the data associated with Landsat-7, MODIS, and ENVISAT may allow for a more quantitative evaluation of coral bleaching.

Papers by L.Tommy Lindell, Petra Ammenberg & Philip Kramer on the detection of a coral bleaching event from high resolution satellite images has been presented at some conferences. Summeries of those papers could be found at Papers. Detection of coral bleaching using high spatial resolution satellites Lank till Paper1.rtf , Mapping of coral bottoms from different high resolution satellite images Lank till Paper2.rtf and Automated change detection of bleached coral reef areas.

IRS Image of Belize

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