Using Remote Sensing Techniques for Coastal Zone Management in Halong Bay, Vietnam

要旨

Coastal zones consist of many fragile ecosystems, in particular, mangrove ecosystems are very sensitive and highly vulnerable. The pressure of increasing population and development has caused a significant proportion of the mangroves to be destroyed. The Halong Bay area is a famous World Heritage site, well known for its biodiversity. However, in recent years, the mangrove ecosystem in this area became degraded. Monitoring the changes of mangrove cover and coastline can provide support for coastal zone management and environmental protection of the bay. Reliable and timely information is therefore required in order to monitor and manage the remaining mangrove resources. The analysis applied integrated techniques of digital image processing: The Normalized Difference Vegetation Index (NDVI) was computed for each date of imagery to derive variations in the vegetation biomass. The interactive stretching techniques helped to detect the range of mangrove from the NDVI image of three dates of Landsat satellite imagery. The Digital Elevation Model (DEM) and moisture indices was also integrated in the logical analysis to support the seperability tidal wetland, and mangrove from vegetation in the inland. Change detection methods were used to calculate the change in mangrove forest cover and coastal zone area over time. The analysis used three different Landsat TM scenes from 1988, 1998 and 2002, and combined results with survey data from 2002. Degraded and rehabilitation mangrove area was quantified by applying an ISODATA unsupervised classification of the RGB-NDVI image. The results show that area of mangroves have been reduced by 21% for aquaculture and tidal wetland was replaced by reclamation, which also gave impact to the coast line and changes the landscape of the bay. The results presented here illustrate the impact of development in recent years and support for coastal zone management.