The absorbing aerosol index from Earth Probe TOMS is the difference between the measured spectral contrast of the 331 and 360 nm wavelength radiances and the contrast calculated from radiative transfer. The absorbing aerosol index has been shown to have a linear relationship to the aerosol optical depth for smoke and dust¹; the larger the aerosol index, the higher the optical depth. It can detect absorbing aerosols over ocean, all types of land surfaces (including snow or ice²), and clouds.

The TOMS images presented here are produced by compositing data from three days of Level 3 data, with the majority of data being provided by the last day. For example, the image for March 1 contains data from February 27, 28, and March 1, with the majority of data from March 1. The data is then smoothed (the smoothing can cause "smearing" over areas containing no data; this situation occurs for images created from partial days).

Please note that, after over 7 years of operation, the performance of the Earth Probe TOMS instrument has degraded and the calibration has been affected. As a result, a noticeable scan bias appears in the TOMS aerosol index data and images.

We will superimpose the NCEP wind and geopotential height at 700 mbar onto the TOMS images when those data become available (usually the next day).

¹ Hsu, N.C. J.R. Herman, O. Torres, B.N. Holben, D. Tanre, T.F. Eck, A. Smirnov, B. Chatenet, F. Lavenu, "Comparisons of the TOMS aerosol index with Sun-photometer aerosol optical thickness: Results and applications," J. Geophys. Res., 105, 6269-6279, 1999.

² Hsu, N.C., J.R. Herman, J.F. Gleason, O. Torres, and C.J. Seftor, "Satellite detection of smoke aerosols over a snow/ice surface by TOMS," Geophys. Res. Lett. 26, 1165, 1999.