langkawi magazine

Nature SECTION

Langkawi Coral Mapping Using Satellite Imagery

Mapping the coral reefs of Langkawi Island during SELIK went hi tech using the 30 meter resolution LANDSAT satellite imagery obtained for the purpose of marine and terrestrial habitat mapping, and subsequently computer processed by expedition members Richard Dorall and S. Gokilan from the Department of Geog raphy, University of Malaya.

Imagery enhancing techniques were applied to differentiate those imagery colours and textures representing possible coral reefs from other marine features such as sand, mud, rock formations, as well as varying classes of sedimentation, and these enhanced images were then geo referenced using computer mapping software to make them compatible with the locational coordinates read five in the field from hand held Global Positioning System (GPS) devices.

These electronic maps were then loaded into an IPAQ Pocket PC, and together with the SILVA MultiNavigator GPS, were used by the coral mapping team to precisely navigate to the location of coral reefs as interpreted from the satellite imagery. (in the map above, brown patches denote coral reefs, green areas denote sand ridges, casuarina trees and hotel development at Tg Rhu, while dark purple areas indicate agricultural vegetation).

Potential coral sites as interpreted from satellite imagery were verified first band by team members using surface snorkeling as well as under water scuba diving, under water reef line transect mapping at selected sites, and detailed site description and under water photography to record the characteristics of the individual reefs.

Coral reef sites mapped using these advanced geographical information technologies and satellite imageries were located in P. Tanjung Dendang, P. Langgun, the Gua Cerita headland, the Sg. Ayer Hangat estuary, and P. Dangli (all in Northeast Langkawi), as well as in P. Singa Besar, P. Beras Basah, and P. Intan Besar in Southwest Langkawi.

"Without satellite imaging and GPS navigation, we would have spent days, possibly weeks, looking for reefs and mapping their spatial geometry," said coral mapping team leader Dr. Azhar Hussin from UM. "With these new technologies, accurate coral reef identification and reef geometry mapping can be done for each reef in, at most, a matter of hours."

Langkawi 1/7/2004