Monitoring of mangrove forests after the major Tsunami disaster in 2004 in Thailand using high resolution satellite data

The Indian Ocean Major Earthquake off the Coast of Sumatra and Tsunami in the Indian Ocean, which occurred on 26 December, 2004, caused much victims and heavy damages in coastal zones. Some studies reported that mangrove forests filled the role of mitigation of the damage by the Tsunami. On the other hand, Mangrove forest themselves suffered both direct and collateral damages of the Tsunami. Direct damages resulted from fierce impacts of the Tsunami and objects damaged by it, and vibration of trunks by repetitious waves of the Tsunami and respiratory disorders from roots due to sedimentation of sands, which were brought by them, caused collateral damages. This study aims to investigate the direct and collateral effect of the Tsunami on mangrove forests. The study area is located at the coastal zone of Ranong, Thailand. SPOT-5 data, which were acquired on 13 March, 2004 (before the Tsunami), 14 January, 2005 (just after the Tsunami) and 26 December 2007, and QuickBird data, which were acquired on 5 April, 2005 and 3 February, 2007 were prepared as high resolution satellite data for this study. The direct damaged areas were extracted from multi-temporal satellite data according to the changes of reflectance property. The middle infra-red information of SPOT-5 was applicable for identifying mangrove forest condition because it responds the water condition on the ground. The collateral damages were evaluated from crown changes derived from multi-temporal QuickBird panchromatic data using the watershed method for crown segmentation. From the crown diameters, which disappeared during two years after the Tsunami, disappeared tree sizes were estimated using allometric equation between crown size and stem diameter, which is a key variable to estimate individual biomass. Field surveys were conducted after the Tsunami to confirm the damages. Though it was difficult to distinguish the damages on mangrove forests from their dynamics, this study made it clear that high resolution satellite data were useful to identify the local changes of canopy of mangrove forests in wide area. Further studies for integrating the results of this study using high resolution satellite data to evaluate the Tsunami disaster on mangrove forests with ecological investigation of mangrove forest dynamics are required.