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Description: Absorbing aerosol index data record provides long-term information about the presence of elevated absorbing aerosols in the Earth's atmosphere. It has been reprocessed with the latest algorithm version (see below). The aerosol types that are mostly seen are desert dust and aerosols from biomass burning and volcanic eruption events.

Type: Data record

Satellites and instruments: GOME-2/Metop-A and GOME-2/Metop-B

Algorithm version: 1.01

Time period: 24/01/2007 - 30/11/2015 (GOME-2/Metop-A) , 12/12/2012 - 30/11/2015 (GOME-2/Metop-B)

Theoretical basis: Global Ozone Monitoring Experiment-2 (GOME-2) measures the radiance spectrum of sunlight scattered from the atmosphere. Absorbing aerosol index is derived from the reflectances measured by GOME-2 at 340 nm and 380 nm.

Processing: The AAI processor is integrated part of the AC SAF processing at the KNMI. The algorithm calculates a ”residue” by using the contrast between the two wavelengths. When the surface albedo is assumed to be constant over the spectral range of the two selected wavelengths, and when the total ozone column is given, all deviations from a fully Rayleigh scattering atmosphere are assumed to be caused by absorbing aerosols. Note that scattering aerosols will be accounted for via an increased surface albedo. The total ozone column needed for the calculation is derived from the ozone climatology or sonde profile, which is selected by the user in the configuration file.

Units and spatial resolution: Absorbing aerosol index is a unitless linear scale, with higher values indicating elevated amount of aerosols present in the atmosphere. Spatial resolution is equal to the spatial resolution of the GOME-2 instrument: 80 km x 40 km (24/01/2007 – 16/07/2013) and 40 km x 40 km (16/07/2013 – 30/11/2015) for Metop-A and 80 km x 40 km for Metop-B.

Validation: This data record is validated by KNMI. Validation is based on satellite-to-satellite comparison: GOME-2 AAI product is compared with OMI-TOMS (EOS Aura) and SCIAMACHY (Envisat) AAI products.

Archiving and dissemination: This product is archived at the FMI and available via data record access page.

File format and size: This product is delivered in HDF5 format, each file containing one satellite orbit (sunlit portion). The size of a single product file is about 800-900 kB.