The Infrared Difference Dust Index: Past, Present and Future

Abstract

The Infrared Difference Dust Index (IDDI) [Legrand et al, 2001] is a Meteosat-derived thermal-infrared (TIR) index dedicated to remote sensing of desert aerosol over land (based on the former Meteosat First Generation (MFG) series). The IDDI product proves to be effective in studies of dust source location and seasonal activity [Brooks and Legrand, 2000; Léon and Legrand, 2003; Deepshikha et al, 2003a; b], in the physics of dust emission with respect to the surface properties [Chomette et al, 1999; Marticorena et al, 1997; 1999; 2004], for description of dust transport [Petit et al, 2005], of dust mineral composition [Caquineau et al, 2002] and for dust (meteorological) forecasting [Hu et al, 2008]. An improved algorithm and a new cloud masking technique applied to full resolution MFG IR images has given rise to an upgraded dust index. These improvements are described in the next section and resulting IDDI images are displayed and compared with images of the UV Aerosol Index (AI) from the Ozone Monitoring Instrument (OMI) aboard EOS-AURA. They are part of a database (to be completed), over the period 1981-2006 covered by MFG. Obviously, the 1-channel IDDI cannot match with the multi-channel data provided by the new spatial instruments (such as MSG/SEVIRI), but it has the advantage of covering a quarter century (1981-2006) and thus it is relevant for climate studies over this period (including the severe Sahelian drought of the 80s) as well as for investigating on the nature of the link between dust occurrence and epidemics of meningococcal meningitis in West Africa, throughout the 25 past years [Martiny et al, 2007]. In the last section of this abstract, the physical bases of dust remote sensing in the TIR during daylight are briefly presented. They allow to understand the fundamental differences with the more usual detection using channels in the solar spectrum (VIS and NIR) and they bear on the favorable or adverse conditions to produce a dust index of quality. Lastly, it is possible from such results to outline an approach for the determination of the TIR dust optical depth (or a dust index closely related to it), using the TIR channels IR8.7, IR10.8 and IR 12.0 of MSG/SEVIRI, as well as its median infrared (MIR) channel IR3.9