Coastal wetland and shoreline change mapping of Pichavaram, south east coast of India using Satellite data Mangroves in India Mangroves distribution in India occupies an area of about 4250 km2 (MOEF, 1994). Due to general intertidal slope and heavy siltation, the delta environment of east coast supports extensive mangroves. The largest stretch of mangroves in the country is located at Sundarbans, which covers an area of about 2119 km2. Next to Sundarbans, the Andaman & Nicobar island mangroves are the second largest, which covers and area of about 966 km2. Small patches of mangroves are found in Gujarat, Maharastra and some other coastal states (MOEF, 1987). In Tamil Nadu, mangroves are well-developed in Pichavaram and Muthupet. The Pichavaram mangrove is a typical swamp, extending between Vellar and Coleroon estuaries. In Pichavaram mangroves sixteen Angiosperm species were recorded, fourteen of them are exclusively mangrove species (Krishnamurthy et al., 1981) Six zones have been demarcated in Pichavaram; Aricenniamarina is dominant in Zone-I; Arthrocnemum indium, Exoecaria agallocha, Salicornia brachiata, Sesuvium portulacastrum and Suaeda maritima are sporadically distributed in the sandy region Zone II includes the bank of three creeks lying parallel to the shore the fringe of shoreward belt is occupied by Salicornia brachiata and the inward belt has Avicennia apiculata, Rhizophora apiculata and R.Stylosa. The inner region is found to have mixed community of Excocaria agallocha and Salicornia brachiata and Arthrocnemum indium occurs in this zone. Luxuriant mangrove vegetation exists in zone III with maximum number of species. The channels fringes areas are bordered by Rhizophora apiculata and R. Muconata, Acanthus ilicifolins and Derris Heterophylla found in the zone IV and A continuous stretch of Suaeda maritima is observed in zone V. Salicornia brachiata is dominant exists in zone VI near Coleroon estuary (Krishnamurthy, 1995) Study Area Pichavaram is located 51 km north east of Chidambaram, Cuddalore district, Tamil Nadu, between latitude 11°20' to 11°30' north and longitudes 79°45' to 79°55' east (Fig.1). It is an estuarine type of mangrove situated at the confluence of Uppanar, a tributary of the Coleroon River. Fishing villages, croplands, and Aquaculture ponds surrounds the area. This mangrove environment is attracting large number of tourists. The Pichavaram mangrove wetland has 51 islets and the total area of the Vellar-Pichavaram-Coleroon estuarine complex is 2335.5 ha of which only 241 ha. is occupied by dense mangrove vegetation. Nearly 593 ha, of this wetland is occupied by helophytic vegetation like Suaeda, 262.5 ha. barren mud flats and 1238.5 ha. Barren high saline soil (Krishnamoorthy et al., 1994) out of the 2335.5 ha of this mangrove wetland only 1100 ha. Comprising the entire mangrove vegetation located in the middle portion of the Vellar-Pichavaram-Coleroon wetland has been declared as a reserved forest. Department of Forest, Government of Tamil Nadu, declared the Pichavaram mangrove as a Reserved Forest.  Fig.1. Study Area Location Map Two major rivers namely Vellar River and Coleroon River in this area drained into Bay of Bengal. The area between the two rivers is identified as brackish water with mangrove vegetation. The area is covered by alluvium in the western part and fluvial marine and beach sands cover eastern part of the area. Geomorphology of area is major area is covered by flood plain, sedimentary plain and beach sand. Major portion of the area falls under nearly level sloping category. During the nine year period from 1990 to 1999 the maximum rainfall of 1844 mm was recorded in 1990 and minimum rainfall of 875 mm was recorded in 1996. The soil group of the area is Hydrological soil group `C' (USDA) low infiltration and moderate runoff potential found 50% area. The soil group `B' with moderate runoff is covering about 45% areas. The remaining 5% area is occupied by soil group `A' with high infiltration low runoff potential. Hence, this study envisages to understanding the overall changes in the wetland ecosystem of Pichavaram mangroves. Satellites and Sensors Earth Resources Technology satellite ERTS-1 launched by NASA later renamed as Landsat-1 for mapping and monitoring of earth resources. Many other countries France launched SPOT; India lunched Indian Remote Sensing Satellite Series (IRS). NASA have been launched five satellites in the series of Landsat, first three and first generation satellites and carried Return Beam Vedicon (RBV) and Multispectral Scanner (MSS) imaging sensors and the second generation satellites carry advanced imaging sensor called Thematic Mapper (TM). Two satellites in the series of SPOT launched by France provide data in MSS and panchromatic spectral band with normal and stereoscopic mode. Indian Remote Sensing satellites series IRS-1A, IRS-1B, IRS-1C and IRS-1D the indigenously developed satellites have been put into orbit 1988, 1991, 1996, 1997 respectively and IRS-1A & 1B carried LISS I and LISS II multispectral sensors, IRS-1C & 1D contains LISS III, with multispectral scanner, panchromatic stereo viewing capability sensor provide good quality data. Image Interpretation and Analysis The satellite data products are available to the scientists in form of photographic products such as films, diapositives and paper prints of geo-coded in various scales or digital data stored in the form of Computer Compatible Tape (CCT) cartridges, floppies and C.D ROMs. The desired information can be extracted from the above data products through visual interpretation and digital image processing techniques. Both visual and digital image analysis techniques are complementary to each other. For large areas and spectrally homogenous scenes digital image processing techniques may provide a quick and cost effective means of image analysis. Smaller areas and spectrally heterogeneous scenes visual interpretation method is more suitable. However in order to bring out the subtle variation and quantitative measurements it is essential to perform the digital image processing techniques since classification of digital data can be done through computers with help of image processing software. Visual Interpretation Techniques Visual interpretation of remote sensing images for extracting desired information could be achieved in an efficient and effective manner by using several basic interpretation keys (or) elements (Floyd F. Sabins Jr. 1987). The basic interpretation keys are i) Tone ii) texture iii) pattern iv) shape v) size and vi) location or association. All these interpretation elements are qualitative attributes and they are subjective depends on the experience and personal bias of an interpreter. Digital Image Processing Remotely sensed data compounds to different earth features collected by the satellite sensors and stored in computer compatible tape, cartridge CD-ROM, floppy in regular line and columns. The pixel represents brightness value having a specific Digital Number (DN) value depends on the reflected energy from the earth surface in a specific wavelength or band or channel. Therefore, each one of the earth features is sensed by the sensors simultaneously and provides a set of DN values. The DN values of each pixel are ranging from zero for black to some higher value (255) for white, based on the radiometric resolution. The availability of remote sensed data in digital form helps in carrying out digital image processing with aid of ERDAS-imagine image processing software. The digital image processing techniques provide flexibility in data handling due to the fact that the digital data can be numerically manipulated by using an equation (or) set of equations to get the desired details in the graphic display (or) pictorial form for further analysis (Lillesand TM and Kiefer RW, 1987) There are many procedures/methods available for image data manipulation they can be broadly grouped into 3 categories viz. 1) Image rectification and restoration also called preprocessing 2) Image enhancement and 3) Image classification. |