Global Emissivity Distribution and Change from 2003 to 2007

Abstract

Land surface emissivity is known to be affected by land cover, surface roughness, and soil moisture. In this study we used land surface emissivity data from National Aeronautics and Space Administration's Advanced Microwave Scanning Radiometer for Earth Observing Systems for 2003 to 2007 to detect areas of significant emissivity change and identify its potential causes. Data distribution of annual emissivity averages on a global scale revealed that the western coastlines of the continents, deserts, and the polar areas showed the lowest emissivity values, whereas the higher emissivity values were concentrated in large cities, heavily forested areas, and large mountain ranges. A two-tailed Z test was then used to identify regions that showed statistically significant changes at the 99 percent confidence interval. At the regional scale, three regions that showed statistically significant annual change values at the 99 percent confidence interval—the Iranian Plateau, the La Plata basin, and the Indus basin—were then isolated. An analysis of variance was then performed to determine whether the variability was due to phenomena across the region or within each region. In the La Plata River basin, areas of significant negative emissivity change (≤–0.0156) were noted, which are associated with deforestation, whereas the areas of significant emissivity gain (≥0.0165) were concentrated in floodplains. In the Indus basin and Iranian Plateau, the significant negative emissivity change was associated with variations in surface wetness. Using emissivity as an indicator of land surface properties can assist in more detailed analysis of changes on the surface of the earth.