SEAGRASS MAPPING IN THUY TRIEU - CAM RANH LAGOONS (VIETNAM) BY USING SATELLITE MULTI SENSORS

摘要

Seagrass canopy plays a critical role in the ecological function of coastal zones. They supply nursery and juvenile habitats for fisheries, stabilize sediment and provide direct food for dugongs and green turtles. The objective of this paper is to detect the distribution and temporal variation of the seagrass communities in Thuy Trieu - Cam Ranh lagoons base on multi sensors such as SPOT5, Orbview-3, FORMOSAT-2 and ALOS AVNIR-2 together to grounth truthing data in April 2013. A pre-processing procedure including geometric correction, radiance calibration, atmospheric correction and water collumn correction. The avoiding of solar glints (if available) mainly base on NIR band of above satellite images. The water collumn correction is the most important step in general procedure of seagrass mapping. In this step, the Bottom Reflectance Index - BRI are calculated base on depth of lagoon or bathymetry map, IOPs data as well as solar and sensor paths. Seagrass beds in Cam ranh coverage of 1178 ha with abundance comunities of Halodule uninervis - Halophila ovalis in the peak of lagoon and mainly of Enhalus acoroides specie in the midle of lagoon. In present time, the seagrass beds in here are being degraded by illegal fishing methods, aquaculture, industry and living domestics. The reducing ratio of seagrass coverage has been increased in recent years.