Desert dust aerosol air mass mapping in the western Sahara, using particle properties derived from space-based multi-angle imaging

Abstract

T E L L U SDesert dust aerosol air mass mapping in the western Sahara, using particle properties derived from space-based multi-angle imaging A B S T R A C T Coincident observations made over the Moroccan desert during the Sahara mineral dust experiment (SAMUM) 2006field campaign are used both to validate aerosol amount and type retrieved from multi-angle imaging spectroradiometer (MISR) observations, and to place the suborbital aerosol measurements into the satellite's larger regional context. On three moderately dusty days during which coincident observations were made, MISR mid-visible aerosol optical thickness (AOT) agrees with field measurements point-by-point to within 0.05-0.1. This is about as well as can be expected given spatial sampling differences; the space-based observations capture AOT trends and variability over an extended region. The field data also validate MISR's ability to distinguish and to map aerosol air masses, from the combination of retrieved constraints on particle size, shape and single-scattering albedo. For the three study days, the satellite observations (1) highlight regional gradients in the mix of dust and background spherical particles, (2) identify a dust plume most likely part of a density flow and (3) show an aerosol air mass containing a higher proportion of small, spherical particles than the surroundings, that appears to be aerosol pollution transported from several thousand kilometres away.

Reducing the Uncertainties in Direct Aerosol Radiative Forcing

“…However, species-specific aerosol chemical and microphysical property validation data can be obtained with much greater detail from surface and aircraft direct sampling. Such measurements can provide the most accurate size distribution, SSA values, and chemical composition currently available, but sampling is extremely limited; coincident aircraft and satellite observations, obtained on fieldcampaign ''Golden Days,'' can critically test aerosol-type retrievals, but only on these very special occasions (e.g., Kahn et al 2009). …”

Improvement of aerosol optical depth retrieval using visibility data in China during the past 50 years

“…The Multiangle Imaging Spectroradiometer (MISR) is another sensor onboard the EOS Terra satellite that provides AOD data over oceans and land and is able to observe targets in the air and on ground in different channels and from different perspectives. The retrieved AOD using MISR data is consistent with ground observations, even over desert, because the sensor makes it possible to accurately account for directional surface scattering in the retrieval procedure [ Kahn et al ., , ; Martonchik et al ., ; Diner et al ., ]. Since the modern research sensors have onboard calibration systems, they are more accurate than the vicarious calibration adopted for the traditional sensors [ Li et al ., ].…”

Eyjafjallajökull volcano plume particle-type characterization from space-based multi-angle imaging

“…For Patch P6, 400 km downwind, a larger fraction of the retrieved grains is weakly (1 % and 4 % hematite) rather than highly absorbing, the retrieved cirrus analogs are mostly small (10 µm) instead of large, and the SSA for the mix of particles increases from ∼ 0.88 near the source to ∼ 0.91 -a small absolute SSA difference, but more robust as a relative indication (e.g., Kahn et al, 2009). Taken together, these results seem to support the idea that as the volcanic plume ages, the average aerosol properties tend toward smaller and brighter particles.…”