Daytime and nighttime detection of mineral dust over desert using infraredspectral contrast

Desert dust has a potentially strong effect on climate and climate forcing as evident from satellite data, yet its detection close to its sources over deserts and semidesert regions is difficult. The lifted dust often has the same mineral composition as the surface sand left behind. The main consist ent difference between airborne dust and surface sand is particle size. Thi s difference is used here to develop a remote sensing technique for the det ection of dust over desert. The technique uses two infrared channels that w ill be on the Earth Observing System (EOS) moderate resolution imaging spec troradiometer (MODIS). It is based on measurements and modeling of the ther mal infrared spectrum of silicate and carbonate minerals that show strong d ifferences between the thermal properties of the smaller dust particles (di ameter of 2-5 mu m) and the larger sand particles (diameter > 70 mu m). In particular, the emissivity of quartz increases with the particle size at 11 mu m and decreases at 8.6 mu m. This different behavior allows use of thes e two MODIS channels to distinguish between variations of the dust temperat ure and surface temperature from the variation in the loading of the smalle r dust particles in the atmosphere. We report simulations of the technique for day and night remote sensing and apply it to high resolution infrared s ounder (HIRS) data which is validated against ground-based measurements by Sun photometers. The technique is found to be sensitive to the dust loading over sand surfaces and not very sensitive to the dust height.