Dust Observations and Climatology - Mineral Dust: A Key Player in the Earth System - page 155

and other regional networks (i.e. EARLINET with lidars over Europe) are of
primary importance for the validation and interpretation of the satellite-derived dust
products. Likewise, the quality and length of the aerosol records they provide at
certain sites make them by themselves well adapted for application to dust research.

7.3 Applications

7.3.1 Source Regions

As mineral dust sources are mostly located in remote and arid regions where ground-
based aerosol measurements are difficult, observations from both geostationary
(Sect. 7.3.1 ) and earth-orbiting (Sect. 7.3.1 ) satellites have played an important role
to identify contemporary dust sources (see also Chap. 3 ) . Among the first aerosol
satellite products used for this aspect are semi-quantitative indices such as the AI
derived from the TOMS/Nimbus 7 (Prospero et al. 2002 ) and the IDDI derived
from Meteosat (Brooks and Legrand 2000 ;seeTable 7.2 ). The analysis of global
aerosol satellite observations, especially the TOMS AI (Prospero et al. 2002 ), has
highlighted that the Sahara desert is by far the most important dust source of the
world. More recently, data from sensors such as MODIS and SEVIRI/MSG have
provided more detailed information on dust sources (Ginoux et al. 2012 ; Schepanski
et al. 2009 ).

Regional Data from Geostationary Satellite

The IDDI is a dust product firstly derived from daily noontime IR images of
Meteosat-1 available over continental Africa over the period 1984-1993 (Brooks
and Legrand 2000 ; Legrand et al. 2001 ). It has been applied for dust source
identification in the Sahara and Sahel, as well as the description of seasonal and
interannual variability (Brooks and Legrand 2000 ). Thanks to the shift of Meteosat-
5-63 ı E, 1 year of Meteosat-IDDI (1999) is available to monitor dust sources in
the arid and semi-arid areas surrounding the North Indian Ocean, highlighting the
Rub Al Khali Desert in central Saudi Arabia as one of the largest dust sources in
this region (Léon and Legrand 2003 ). Vergé-Dépré et al. ( 2006 ) have investigated
methods to improve the IDDI, which is sensitive to water vapour and surface
temperature. A recent progress for the investigation of North African dust sources
is based on the SEVIRI/MSG thermal IR radiance measurements (Schepanski et al.
2007 ). One of the main advantages of this product is to provide observations of dust
source activation at 3-hourly resolution (Schepanski et al. 2009 ). Thus the diurnal
cycle of dust emission over the Sahara has been investigated and better understood
in view of meteorological controls. Based on 2 years of SEVIRI/MSG dust index
data, Schepanski et al. ( 2009 ) show that emissions peak in the hours after sunrise