Evaluation of Coral Systems through Remote Sensing - A case study in Nicobar Islands, India
M.V.R. Murti, B. Babu Madhavan, B. Krishna Mohan and G. Venkataraman
Centre of studies in Resources Engineering, IIT, Bombay, India
Abstract
Studies on corals of Andaman and Nicobar islands are limited and these deal essentially with coral and reef resources. In the present study image processing techniques have been used on Landsat TM digital data to bring out different coral systems. Discussions are presented on the extent and the feasibility of mapping and monitoring the geomorphological zone of reefs through digital processing of the Landsat - 5 TM data. The classifications made in this investigation are based on color reflectance of submerged features. While it is an accepted fact that water depth affects the color and volume reflectance of submerged features, band 2 of TM is analyzed for submerged / exposed reefs with varying bathymetric elevations and morphological features. But this investigation initiated a digital and comparative techniques for remotely sensed data for submerged reefs. With the aid of bathymetric charts and coastal geomorphology map (derived from topographic maps) probable locations of different coral systems have been delineated based on their extent and evolution stages and are presented as coral maps.
1. Introduction
Coral reefs are a tropical, shallow water ecosystem, largely restricted to the area between the latitudes 30 degree N and 30 degree S. Corals generally have very specific environmental requirement for light temperatures, water clarity, salinity and oxygen. Even in the clearest seas, reef-building corals are restricted to depths of less than 30m and are generally found much shallower (Coral Reefs 1988). The Andaman-Nicobar islands have extensive well developed reefs. All the islands in Andaman and Nicobar have fringing reefs, and their extent away from the shore can be easily obtained form hydrographic/navigational charts (Wafer, 1986). The islands are roughly between 7° N and 8°N.
The present work attempts at locating zones of coral activity through the analysis of remotely sensed data with the aid of bathymetric and thematic maps. Corals encountered, have been categorized into several classes based on their location, evaluation and extent.
On coral reef resources management, studies are now being conducted to determine the extent of useful information derivable from Landsat coral reef images from digital analysis. By using Landsat data, Smith et al. (1978) categorized and mapped the physiographic zones of Australian Great Barrier reef (Cape Melville area) by automated processing of Landsat (ERTS) data and they evaluated them with respect to aerial photographs. Major
physiographic zones and bottom cover types of Apo reefs have been categorized and mapped using combinations of unsupervised and supervised modes of digital processing by Ricardo (1978), Significant studies about Indian Coral reefs include Ahmed (1972), Pillai (1983, 1983b) and wafer (1986).
