Urban Growth Monitoring and Analysis of Environmental Impacts on Bankura-I and II Block using Landsat Data

Abstract

This study put forward a technique to estimate and monitor the urban built-up land features from Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) imagery taking into account of two blocks in Bankura District, West Bengal as examples. In this study three indices have been selected, viz., Normalized Difference Built-up Index (NDBI), Normalized Difference Water Index (NDWI), and Normalized Differences Vegetation Index (NDVI) to represent three major urban land-use classes, built-up land, open water body and vegetation respectively. Consequently, the seven bands of an original Landsat image were reduced into three thematic-oriented bands derived from above indices. The three new bands were then combined to compose a new image. This considerably reduced data correlation and redundancy between original multispectral bands, and thus significantly avoided the spectral confusion of the above three land-use classes. As a result, the spectral signatures of the three urban land-use classes are more distinguishable in the new composite image than in the original seven-band image as the spectral clusters of the classes are well separated. Through logic calculation on the new image, the urban built-up lands were finally extracted with overall accuracy ranging from 91.5 to 98.5 percent. Therefore, the technique is effective and reliable. In addition, the advantages of over NDVI and over NDWI in the urban study are also discussed in this paper.