Use of Remote Sensing and GIS to Quantify the Temporal Landcover Changes of Coral Reefs of Gulf of Mannar, South India I.Saranya 16, Rajarajeshwari Nagar Koothapakkam Cuddaore-607002 Contact number: 9840834769  Pon.Suriya New No. 6, I floor Daniel Street Adambakkam Chennai-88 Contact number: 9840849553 G.T.Mahalakshmi Bargavi 24/56 Kumaran Nagar Extn-2 Chennai-50 Contact number: 044-26548240  S.Sadhvi 11, Kongu Nagar Mogappair Chennai-37 Contact number: 9444465233 Dr.S.Sanjeevi Abstract Coral reefs are massive, organic limestone structures, which at as a barrier against wave action along the coastal areas and support rich and diverse marine aquatic life forms. The coral ecosystems, however, are facing threats of destruction due to natural causes such as erosion, accretion, wave action, littoral currents, sea level variation and due to anthropogenic causes such as construction of break waters, discharge of effluents and mining of coral reefs. To conserve and manage coral ecosystem it is essential that we monitor the temporal changes that have occurred in the coral islands. This study which uses RS and GIS techniques is concerned with a group of 10 coral islands between Rameshwaram and Tuticorin in the Gulf of Mannar region, which was declared as a marine biosphere reserve. Multi temporal satellite images acquired by Landsat-II MSS (1979), Landsat-IV TM (1988&1992), Landsat-VII (2000&2001) ere interpreted and changes in the landcover were mapped. The methodology involved selection of appropriate bands, generation of NDVI images and comparison of the vegetation density for the islands. When analyzed, in a GIS environment, it is noticed that the landcover has been fluctuating with an increase and decrease in vegetation, sand and water bodies over a period of 22 yeas. These changes maybe attributed to coastal erosion, sediment deposition, rainfall fluctuation and the cyclonic regimes including human intervention in the form of coral mining. This study has demonstrated the potential of multi temporal satellite images and GIS for effective monitoring and management of the coral ecosystems. INTRODUCTION: Coral reef ecosystem has high biological diversity with the greatest number of species than any other marine ecosystem. Coral reefs act as a barrier against wave action along the coastal areas and prevent coastal erosion. In addition, coral reefs protect mangroves and sea grass beds along the shore. These also serve as important breeding, nesting, berthing, nursing and feeding areas for many varieties of economically important fishes and organisms. Coral reefs are highly productive with annual production rates ranging from 2000-5000gC/m² per year. Such a higher rate of productivity is due to efficient retention and recycling of nutrients within the reef system. The potential fish yield from the world reefs is 6-9 million tones per year, equivalent to 9-12% of all the marine fish catch. OBJECTIVE: The aim of this work is
NEED FOR STUDY: In most of the islands, the vegetation is continuously changing due to various factors and the coral reef deposition is tremendously increasing. The coral islands have multifaceted uses. But these islands face numerous threats due to natural causes like storm, waves and man-made causes like quarrying. Vast areas of corals have been deployed for man’s selfishness. Thus, there is a dire need to keep a check on growth of corals in par with utilisation of the coral resources. Failure of which will lead to imbalance in the coral ecosystem. Hence, there is a need to study the temporal changes in landcover of Gulf of Mannar. STUDY AREA: Gulf of Mannar extends to 140 km in SW-NE direction between 78?05’ and 79?30’ E longitudes and 8?47’ and 9?15’ N latitudes and it covers and area of about 10,500 km². There are 21 islands out of which 10 islands say, Van Tivu, Koswari Tivu, Kariya Shuli Tivu, Uppu Thanni Tivu, Nalla Thanni Tivu, Anaipar Tivu, Palliyarmunai Tivu, Appa Tivu, Talairi Tivu, Musal Tivu are considered. The Gulf of Mannar is endowed with a combination of eco-systems including mangroves, sea grass, sea weed and coral reef. GIS DEFINITION: GIS consists of a powerful set of tools for collecting, storing, retrieving, transforming and displaying spatial data from the real world. It is a database system in which most of the data are spatially indexed, and upon which a set of procedures operated in order to answer queries about spatial entities in the database. GIS differs from computer graphics in terms of spatial relationships because the latter are largely concerned with the display and manipulation of visible materials. The information obtained from various sources (maps …etc), are digitized and stored in a geographic information system, database is created that can be queried to produce appropriate road model for optimal route analysis .GIS allows for the query and manipulation of the database to compute new characteristics by logical and arithmetic operations on the existing data and linkage of attribute and image databases to provide necessary models. The GIS can be used to create data files by digitizing the boundaries and arcs of the network into graphic database and storing the relevant data into the attribute database. COMPONENTS OF GIS: GIS has three important components
The general hardware components of GIS are
Data input covers all the aspects of transforming data captured in the form of existing maps , field observations , and sensors( including aerial photography , satellites , and recording instruments) into a compatible digital form .Data input is the operation of encoding the data and writing them to the database. Two aspects of the data to be considered (GIS)
Errors can arise during encoding and input of spatial and non-spatial data. Some of the errors which normally occur are given below:
Data storage and Database management system concerns the way in which the data about the position,linkages and attributes of geographical elements are Structured and organized. There are basically two methods of storing data:
The raster form consists of an array of grid cells, each grid is referenced by a row and column number and it contains a number representing the type or the value of the attribute. Data output and presentation Data output and presentation concerns the way the data are displayed and the results of the analysis are reported to the users. User- compatible output is in the form of maps ,graphs ,and tables while computer –compatible output maybe in the form of a magnetic tape that can be read into the another system. User- compatible output devices can be classified into those that produce ephemeral displays on electronic screens and those that produce permanent images on paper, Mylar sheet or other materials. Electronic displays are known as visual display units or graphic terminals, the hard copy devices as plotters. Data transformation Data transformation embraces two classes of operations, namely transformation needed to remove errors from the data or to bring them up to date or to match them to other datasets and analysis applied to the data to extract useful information. III. Organizational aspect of GIS For any use of GIS to real world problem appropriate organizational contexts is essential. To perform this properly not only the necessary investments in hardware and software is required but also a new technology in the proper organizational contexts. Skilled personnel and reasonably priced software are required. SOFTWARES AVAILABLE: The general commercial GIS softwares available are
The satellite data used for the study are LANDSAT TM of 1988-92, LANDSAT MSS of 1979 and LANDSAT ETM of 2000-2001. Digital Image Processing The satellite data, Landsat-MSS, Landsat-TM and Landsat-ETM, obtained consists of separate bands each as a separate file. The bands of each sensor are layerstacked in a single file by choosing the appropriate bands and their corresponding FCC are generated. The bands for layerstacking are chosen such that Normalised Difference Vegetation Index (NDVI) the system uses the appropriate algorithm. It is a satellite metric used to detect changes in pixel scale vegetation greenness. The NDVI is preferred to the simple index for global vegetation monitoring because it helps compensate for changing illumination conditions, surface slope, aspect and other extraneous factors. The highest NDVI value is assumed to represent the maximum vegetation greenness during the period. Clouds, snow and bright non vegetated surfaces have NDVI values of less than zero. The index is computed from the following equation: NDVI = [NIR – RED] / [NIR + RED] Subsets for each island for the three data sets are created. Bands from the following satellite sensors can be used to calculate NDVI:
Interpretation and Digitization Visual interpretation is best learned through the experience of viewing hundreds of remotely sensed images according to the requirements of specific fields of application. Various elements of visual interpretation,
RESULTS AND DISCUSSION: Index values can range from -1.0 to 1.0, but vegetation values typically range between 0.1 and 0.7. Higher index values are associated with higher levels of healthy vegetation cover, whereas clouds and snow will cause index values near zero, making it appear that the vegetation is less green. A range of errors such as scattering by dust and aerosols, Rayleigh scattering, subpixel-sized clouds, plus large solar zenith angles and large scan angles all act to increase red value with respect to near infra red and reduce the computed NDVI. NDVI = (NIR-RED) / (NIR+RED) Multi-date satellite data used in the present study enabled observing changes in coral reef area in Gulf of Mannar from 1979 to 2001. Over the past 22 years, area of some reef classes has decreased and some has increased. Island erosion and accretion are caused mainly by the action of waves and wave-induced current. All islands are made up of a calcareous frame work of dead reef and sand. They have a sandy coast and some have a rocky coast. Fringing reef along the windward side of islands protects the islands from direct wave action. The morphological variations of islands occur due to natural anthropogenic stress. There is change in shape and size which is clear from imageries through visual interpretation.    CONCLUSION: Remote sensing and GIS techniques were used to quantify the temporal changes. This study clearly indicates the deterioration of coral reefs. It needs to be managed to preserve the coral ecosystem. REFERENCES:
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