Dust Observations and Climatology - Mineral Dust: A Key Player in the Earth System - page 162

Fig. 7.6 Global mean AOD at 865 nm ( left ), mean Angström exponent ( right ) retrieved over
clouds from POLDER-3 in summer 2009 (Courtesy of Peers and Waquet)
values retrieved by each sensor, as, for example, MODIS provides more extensive
coverage than MISR.
As shown by Kalashnikova and Kahn ( 2008 ), the approach combining infor-
mation from different satellite sensors such as MODIS and MISR is valuable to
better analyse the evolution of dust properties during transport and to increase
coverage. Studies based on daytime polar-orbiting satellites can be complemented
by measurements from the new generation of high-resolution IR spectrometers
and interferometers, which allow for dust characterization at night. Klüser et al.
( 2011 ) present an algorithm for retrieval of DOD from IASI on the Metop satellite,
allowing for dust observation at day and night. Several recent studies (Pierangelo
et al. 2004 ; DeSouza-Machado et al. 2010 ; Peyridieu et al. 2010 )haveshown
that some information on dust altitude and effective particle size can be retrieved
from AIRS data. Additionally, as highlighted by Yu et al. ( 2013 ), geostationary
measurements have been underused up to now. Thieuleux et al. ( 2005 )have
shown, based on SEVIRI/MSG data, that finer temporal resolutions during the
day not only allow monitoring of dust properties at higher frequencies but also
remarkably increase spatial coverage compared to what is produced by polar-
orbiting sensors.
Another important aspect in terms of dust observation is the limitation of
satellite passive remote sensing to cloud-free conditions. Thus, until very recently
and the advancement of lidar techniques (see Sect. 7.3.4 ), most of the satel-
lite dust observations were limited to clear sky conditions. Today, new satellite
algorithms are being explored to retrieve natural and man-made aerosols above
clouds from passive sensors like OMI and POLDER (Waquet et al. 2013a , b ).
Figure 7.6 shows an example of new insight provided by POLDER-3 measure-
ments in the A-Train, with aerosol above cloud properties at a global scale
in summer 2009 (Waquet et al. 2013b ). Mineral dust or mineral dust aerosols,
associated with low Angström exponents and high AOD values, are detected
for this season within the “dust belt” region of the Northern Hemisphere. The
computed mean POLDER-3 aerosol optical thickness at 865 nm is 0.456 for
summer dust in 2009, a value that may be considered as a minimum con-