This scene shows a large cloud of dust blowing from northeastern Africa across Egypt, the Sinai Peninsula, over Israel and into the Middle East region on March 19, 2002. It is actually a composite image from two data sources. The true-color image of the surface was made using Moderate-resolution Imaging Spectroradiometer (MODIS) data. A false-color representation of Total Ozone Mapping Spectrometer (TOMS) measurements of aerosol index was overlain to show the extent of the dust cloud.
The aerosol index is a measure of how much ultraviolet light is absorbed by the aerosol particles within the atmosphere, and is approximately equal to the optical depth. Red areas indicate high aerosol index values and correspond to the most dense portions of the dust cloud. Yellows and greens are moderately high values. The TOMS reflectivity data shows that there were relatively few clouds in the area that day. While TOMS cannot see through clouds, the aerosol index value for clouds is zero, so that any small clouds in the region would be ignored, while still detecting the aerosols between and above the clouds.
Image courtesy Jay Herman, TOMS Aerosol/UV Project Principal Investigator, NASA GSFC