Sunderban a GIS approach Use of Remote Sensing & Arial Image in Mapping 
All of the pictures received from remote sensing and which we view on the computer are 8-bit digital images, which means that they have 256 colors (2^8). The image in the right illustrates this principle. Digital images are tables of numbers, which in this case range from 0 to 255. The "bright" squares (called pixels) have high number values (ie. 200 to 255), while the "dark" pixels, have low number values (ie. 50-100). This image is an extreme close-up of a satellite image of West Hancock. The dark region is a stream valley, which has low reflectance, while the bright area is a gravel pit, which has high reflectance. The satellite sensor records the reflectance in its field of view, and then scales the signal to an 8-bit number (0 to 255). Remote sensing is the science and art of obtaining information about a phenomenon without being in contact with it. It provides a unique perspective from which to observe large regions. Sensors can measure energy at wavelengths which are beyond the range of human vision (ultra-violet, infrared, microwave). Compared to traditional satellite remote sensing IRS-1D also, provides significantly higher resolution. It has the ability to collect both panchromatic and multispectral images of the same object from the same perspective. The collected imagery can be output as one-metre pan-sharpened (color) and 4 metre multispectral (color). These images provide excellent accuracy for mapping surface of the earth. Remotely sensed images contain both spectral and spatial information. The spectral information provides various properties and characteristics about the surface cover at a given location or pixel (that is, vegetation and/or soil type). The spatial information gives the distribution, variation, and topographic relief of the cover types from pixel to pixel. Therefore, the main characteristics that determine a pixel's brightness/reflectance and, consequently, the digital number (DN) assigned to the pixel, are the physical properties of the surface and near surface, the cover type, and the topographic slope. In this application, the ability to detect and map lineaments, especially those related to fractures and faults, is critical. Therefore, the extraction of spatial information from the digital images was of prime interest. Cadastral Level Mapping is needed for this type of projects, which is only possible with Arial Survey. We can create 1:10,000 level map with the help of this survey. The Satellite Remote Sensing data has proved to be a highly reliable for extracting the land use, land cover, the river and its bank etc. of any region in a given time and also in a cost effective manner due to their inherent capability of providing very high spectral and radio-metric integrity and consistency. Due to these capabilities satellite remote sensing also facilitates rapid but accurate changed detection studies which also forms an integral components of environmental impact assessment and to site a location for sustainable developmental growth of the entire conservation area. GIS in land mapping: With GIS techniques, maps are produced that are similar in appearance to hand-drawn maps; to the eye, each elevation map may appear not to conflict with the elevation maps of other stratographic units. However, to develop a truly internally consistent set of maps, the maps are processed into a raster (gridded) format. Then, conflicts in elevation between horizons (and larger conflicts across several horizons) detected in reference to block maps. The Topo survey maps always provide some benchmark and are therefore very useful in contour preparation either manually or electronically. Topographical maps of India made by Survey of India were started more than hundred years ago. Since then the land information is based on the Topo Maps of Survey Of India for various purpose. But there is some constraint in Topo maps as information is little bit older. So Topo Maps could be very helpful to read with the Remote Sensing Images, which is today’s scenario. 
Now, it is needless to say that anyone can derive contour maps at various intervals from various Topo maps at various scales. According to Survey of India 10m, 20m and 30m interval contour data are available from 1:25000 and 1:50,000 scale maps Digitized block maps provide the necessary frame of the map to be drawn and also help in physical verification in the field for the errors that might occur inspite of high precision of the imaging. In mapping a terrain especially when in plane it is highly possible that errors may occur in defining the slope and elevation through imaging. On the other hand reliance on entire manual process may also lead to error due to failure of estimation through human eyes. |