Observed decadal changes in extent of mangroves and coral reefs in southern Gulf of Kachchh using principal component analysis and geo-spatial techniques: a case study

The identification of temporal change in the extent of coral reefs and mangroves patches along the Narara and Kalubhar islands was performed using multi-temporal data from 1999 to 2010 (LISS III and LISS IV (MX)). For extracting coral reefs, the reflectances of the feature were studied and using a few sample locations identified by sea-truthing, the reflectances of the corals were observed in different bands. Since these values were not normally distributed, it was considered best to use the modal value of the dataset. The final range was taken as ±1 from the mode, which was used for the extraction of coral pixels. The findings suggested that the coral cover depleted from 19.35 to 9.11 km2 in the study area. The second objective of extracting the mangroves was accomplished by employing the technique of Principal Component Analysis (PCA). This technique gave better results as it not only identified the mangrove swamps but also differentiated between the dense and sparse. The greatest variance in the dataset could be identified by this method, thereby making it easier to outline the variations existing within the mangroves. The findings highlighted that out of the total area mangroves covered 38.81 km2 in 2010 while in 1999, they covered only 30.69 km2 ascertaining the impact of mangrove restoration projects functioning in the area.