Research on the Extraction Method of Coral Reef at Spratly Islands Using SPOT5
Coral reef plays an important role in marine ecosystem.Extracting coral reef information with remote sensing starts late in China and is mainly based on visual interpretation.This paper tries to extract the component information of Swallow Reef and Dallas Reef in Nansha Islands automatically using SPOT5 10 m multispectral data,aiming to explore its identification capability of subsurface information of coral reef.First,the remotely-sensed information was separated into two parts using threshold segmentation method:information above the sea surface and that below the sea surface.After implementing Deglint correction on the latter part of information and introducing a derived band from SPOT5 with it,these images being grouped into 4 different kinds of combinations,were classified using maximum likelihood method.At last,the classification results are compared with QuickBird images,which are regarded as the truth data when the ground data is absent.Results indicate that Deglint correction can reduce the surface noise effectively.NIR band may help avoid the errors in classification caused by the different depth of the sea in some extent.The effect is not as good as expected when the derived band takes place of NIR.In sum,through processes designed in this paper,we could use SPOT5 10 m multispectral data to map components of the coral reef at more than 80% accuracy.