Remote sensing based habitat mapping of Vankalai coral reef, Sri Lanka

Abstract

Coral reefs are an important coastal eco-system in Sri Lanka. Current study was conducted on Vankalai area regarding to develop new method of remote sensing technique to mapping and monitoring the particular coral reef ecosystem. Downloaded Landsat 8 satellite images were processed under the three headings which are preprocessing, processing and post processing. Image preprocessing is used to eliminate errors in satellite images. Depending upon the source of error, inadequacy revision and imperfection expulsion are separated into two types such as radiometric correction and geometric correction. In radiometric correction the foremost requirement is to conversion of DN values to spectral radiance values. And the next step is conversion of radiance values to Top of Atmospheric (TOA) reflectance which could be identify as a unit less ratio measurement. Normalized difference water index was used to enhance water features and suppress the land area. Different types of bottom substrates were identified using Depth invariant index (DII) for study area and which are classified according to the bottom substrate using unsupervised classification. Five types of different spectral classes were identified using developed method which are coral reef, rough bottom, vegetation cover, sandy bottom and deep muddy area. These spectral classes are related to elevation of benthic habitat. Ultimately map was generated with regarding to the bottom substrate for particular study area using Landsat 8 image. It is an extensive reef area but lack of details yet. This study is the first attempt to use Landsat 8 for coral reef mapping in Sri Lanka.