ATSR Aerosol_cci ORAC

World Meteorological Organization

ORAC is one of the three ATSR-2/AATSR ECV products being produced by ESA Aerosol_cci project. The ORAC retrieval is an optimal estimation scheme, which makes use of the dual-view measurements from the ATSR instruments to provide aerosol optical depth, effective radius and surface reflectance at 0.55, 0.67, 0.87 and 1.6 μm. The dataset aims to provide a long-term, consistent record of global AOD for climate studies.

Example results (mean AOD for 2008)

Satellite ERS-2 (ESA), ENVISAT (ESA)
Instrument(s) ATSR-2, AATSR
Algorithm PI Gareth Thomas (STFC RAL Space)
Contact Details gareth.thomas[at]

AOD at 0.55, 0.67, 0.87 and 1.6 μm, Ångström exponent, effective radius*, dust-, absorbing- and fine-mode-AOD at 0.55 μm*. Spectral surface albedo* at 0.55, 0.67, 0.87 and 1.6 μm. Limited aerosol type information (best fit model). (Parameters marked with * are experimental, and unvalidated)

Aerosol algorithm ORAC dual-view
Cloud screening

ESA Cloud Flag (ocean) / Stevens Cloud Flag (land) + additional algorithm specific tests.

Aerosol model Aerosol_cci common aerosol components (de Leeuw et al., 2013)
Retrieval assumptions

Ocean BRDF constrained by sea surface reflectance model driven by ECMWF 10 m wind fields

Retrieval limitations Retrieval over land becomes poorly constrained at high optical depths, due to limited sensitivity to the surface
Spatial, temporal coverage 1995-2012, global (2000/2008 test data available only as of Jan 2015)
Spatial, temporal resolution 10 km – 1×1°. 512 km swath width. 16 day repeat cycle
Operations status reprocessing
Validation status Intercomparison with ground-based, airborne and other satellite data
Quality control Uncertainty handling by optimal estimation. Product also contains quality flag (high/low confidence)
last algorithm version v02.02 (12/2013)
last validation 12/2013


Algorithm description Product format description
Version explanation Validation summary


Product data access
Image / quicklook data access