Estimation of Land Surface Temperature to Study Urban Heat Island Effect using Landsat ETM

Abstract

Abstract The urban air temperature is gradually rising in all cities in the world. One of the possible causes is the drastic reduction in the greenery area in cities. The distinguished climatic condition termed 'Urban Heat Island' (UHI) is developing in the rapidly urbanized cities. Vijayawada city of Andhrapradesh is experiencing rapid urbanization that has resulted in remarkable UHI. Understanding the distribution of Land Surface Temperature (LST) and its spatial variation will be helpful to decipher its mechanism and find out possible solution. This study tries to investigate and identify land use types which have the most influence to the increase of ambient temperature in Vijayawada city. For the present study Landsat ETM+ images of 2001 was obtained from USGS for the study area. Using bands 1-5 and 7 of the pre-processed images the land use / cover pattern was mapped by supervised classification with the maximum likelihood classification algorithm of ERDAS imagine 9.1 software. Five classes considered for the study are Built-up land, Barren Land, Water bodies, Agricultural fields and Vegetation. Normalized Difference Vegetation Index (NDVI) image was developed. The digital number of thermal infrared band is converted in to spectral radiance using the equation supplied by the Landsat user's hand book. The effective at-sensor brightness temperature is obtained from the spectral radiance using Plank's inverse function. The surface emissivity based on NDVI classes is used to retrieve the final LST. It was noted that maximum air temperature was observed in built up areas of the city and minimum temperatures are observed in areas where vegetation cover is more. Urban heat island phenomenon is evident from the LST images. NDVI is found to have negative correlation with LST. The study reveals that appropriate strategies are necessary for the sustainable management of the urban area. Key words: Urban Heat Island, Land Surface Temperature, Land Use/Cover, NDVI INTRODUCTION Urban growth and sprawl have severely altered the biophysical environment. Rapid urbanization has significant influence on different aspects of the quality of life and research in determining the patterns of urbanization and quantifying their impacts is the need of the hour. Unplanned urbanization an urban sprawl will directly affect the land use and land cover of the area. The changes in land use/cover include loss of agricultural lands, loss of forest lands, increase of barren area, increase of impermeable surface of the area because of the built up area, etc. Development of land use land cover is very much useful to the city planner and policy makers. For the sustainable urban ecosystems the amount of land required for growing the vegetation can be estimated from these studies. One of the major implications of urbanization is increase of surface temperature and development of Urban Heat Island. Surface temperature is increased by anthropogenic heat discharges due to energy consumption, increased land surface coverage by artificial materials having high heat capacities and conductivities, and the associated decrease in vegetation and water pervious surfaces which reduce the surface temperature through evapotranspiration. Landsat ETM images are widely used to observe and model the biophysical characteristics of the land surface. In addition to the development of Land use/cover maps band 6 of the Landsat imagery is useful for deriving the surface temperature. Several researchers used the Landsat imagery to develop land use/cover images as well as temperature images