Detection properties of dust and sandstorms by using AVI of MODIS data

Abstract

The detection properties of dust and sandstorms (DSS) by using AVI are examined. The aerosol vapor index (AVI) is defined as AVI=T12-T11, where T12 and T11 are the brightness temperatures at 12 mu m and 11 mu m wave lengths, respectively. MODIS data of Terra/Aqua satellites from China to Japan in April 2006 are used. The AVI vs. T11 scatter charts in narrow regions are made. The narrow region means the region which is smaller than about 100km x 100km. Gu et al. (2003) gave a BTD vs. T11 chart which was based on the radiative transfer calculation in the case of the existence of a DSS layer between the ground and the satellite, where BTD=-AVI. The AVI vs. T11 scatter charts are compared with the true-color images, the T11 images, the AVI images and the result by Gu et al. The results are as follows: (1) The larger the AVI value is, the larger the optical thickness of DSS is, in the case of narrow region over land or over sea with DSS that does not include clouds. The AVI value decreases, in the case of narrow region with DSS that includes clouds. (2) When the DSS is consecutive over land and sea, the AVI value over the land near the boundary of land and sea is about 0.2-2.3K higher than that over the sea, because of the radiative characteristics of land and sea. The AVI value and the T11 value of a pixel (1km(2)) over the boundary of land and sea are changed by the ratio of land area and sea area.