Comparison of AATSR and SEVIRI aerosol retrievals over the Northern Adriatic

Abstract

A case-study is presented comparing the Oxford-RAL retrieval of Aerosol and Cloud (ORAC) algorithm, applied to AATSR and Meteosat-8 SEVIRI data, and the dual-view AATSR aerosol retrieval developed at TNO. The study compares data from an AATSR overpass of the Northern Adriatic and Po Valley region on 4 September 2004, during which time there were two AERONET sunphotometer stations operating in the Venice region as part of the ADRIEX campaign.We present the results of a comparison of the optical depth determined from the two AATSR retrievals and the SEVIRI retrieval at the time of the AATSR overpass. The comparison shows that the satellite retrievals consistently overestimate the aerosol optical depth compared to the AERONET site. A possible reason for this over sea is an inability of the algorithms at present to take into account the ocean colour of coastal waters. Future improvements to the algorithms are suggested.

Mineral dust aerosols over the Sahara: Meteorological controls on emission and transport and implications for modeling

“…The most important products of the now extensive satellite record are (1) a near‐global, long‐term record of aerosol indices and AOT available from early satellite sensors such as Total Ozone Mapping Spectrometer (TOMS); (2) the ability to distinguish aerosol types in transport plumes on the basis of physical properties; and (3) more spatially and temporally resolved properties of atmospheric aerosols from the more recent sensors, including estimates directly over the Sahara desert, most notably from MODIS Deep Blue, MISR, Ozone Monitoring Instrument (OMI), CALIOP, ICESat, and SEVIRI (see Table 1 for more details). Recent developments of particular relevance to understanding Saharan dust processes are (1) the ability to retrieve quantitative AOT estimates over bright desert surfaces at high spatial resolution from nadir‐viewing MODIS data (the “Deep Blue” algorithm of Hsu et al [2004]) and from multiangle visible data from MISR [ Diner et al , 2005]; (2) estimates of AOT at 15 min temporal resolution from SEVIRI visible and infrared channels [ Brindley and Ignatov , 2006; Thomas et al , 2007; Carboni et al , 2007], in addition to the qualitative SEVIRI dust product (see “Best practices for RGB compositing of multi‐spectral imagery,” European Organisation for the Exploitation of Meteorological Satellites guide, available at http://oiswww.eumetsat.org/SDDI/html/doc/best_practices.pdf; an example is shown in Figure 3a); (3) estimates of aerosol properties from Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL); and (4) remarkably detailed vertical profiles of aerosol backscatter from the CALIOP (and to a lesser extent ICESat) spaceborne lidar, albeit with a limited temporal sampling. The example given in Figure 3b demonstrates clear evidence of a widespread deep dust layer over the Sahara.…”

Spectral surface albedo over Morocco and its impact on radiative forcing of Saharan dust

“…Inconsistencies between several retrieval algorithms using data from various satellite instruments are shown in a study by Kokhanovsky et al (2007): the different approaches to the surface‐aerosol signal separation yield ‘not always […] consistent values of the aerosol properties’, while the retrieval is further complicated by the need of a priori assumptions about the scattering phase function and the single‐scattering albedo of the aerosol particles. In a comparison of single‐view and dual‐view techniques of the retrieval of AOD from satellite data, Thomas et al (2007) find that the dual‐view approach yields better results over land because it is less dependent on assumptions about the surface reflectance. But even with MISR's nine viewing angles, some assumptions are required to derive the combination of surface and atmospheric properties from TOA radiance measurements alone (Kahn et al, 2007; Martonchik et al, 2008).…”

Joint retrieval of surface reflectance and aerosol optical depth from MSG/SEVIRI observations with an optimal estimation approach: 1. Theory

“…This ratio might change according to the illumination and viewing conditions [ Levy et al , 2007a]. Thomas et al [2007] applied an algorithm based on the OE theory where the prior information on the surface albedo relies on the MODIS surface BRF product [ Jin et al , 2003]. The method proposed by Thomas et al [2007] includes a rigorous mathematical use of a priori information, but relies on a data set which are acquired at a different spatial and temporal resolution.…”

“… Thomas et al [2007] applied an algorithm based on the OE theory where the prior information on the surface albedo relies on the MODIS surface BRF product [ Jin et al , 2003]. The method proposed by Thomas et al [2007] includes a rigorous mathematical use of a priori information, but relies on a data set which are acquired at a different spatial and temporal resolution. The surface albedo is retrieved by first assuming an albedo spectral shape for the 0.55, 0.67, 0.87 and 1.6 μ m channels.…”