Identification and mapping of coral reefs using Landsat 8 OLI in Astola Island, Pakistan coastal ocean

Abstract

Recent field surveys have reported the presence of corals in many places in the Pakistan coastal ocean; Astola Island especially has been a subject of interest with regards to corals and overall marine biodiversity, and has in fact recently been declared Pakistan’s first Marine Protected Area. This study presents an analysis of coral reefs identification and their spatial distribution through optical satellite remote sensing in the surrounding area of Astola Island. Besides remote sensing data, the study considers sea survey data collected by divers in recent years. A benthic map of ocean ecosystem habitats is generated, through processing of Landsat 8 OLI (Operational Land Imager) imagery. The satellite data was selected at low-tide time to get maximum sunlight penetration in shallow water. Water-column correction was used to generate the depth-invariant index on multiple band-pairs. Water column corrected depth-invariant index bands were then segmented and classified through object-based classification. The results from the remote sensing data processing over Astola Island show good agreement with the field survey data, with nearly all the field survey points of coral reefs falling within the coral reefs class. Use of remote sensing imagery such as Landsat 8, and application of the water column correction method can allow for regular monitoring and management of coral reefs and other benthic ecosystems in the coastal ocean of Pakistan and coastal Arabian Sea.