IMARS Mineral Dust and Ice Cloud Retrieval for IASI

Mineral dust and ice cloud optical depth at 10µm is retrieved over land and ocean with a probabilistic trispectral brightness temperature differnce apporoach based on pseudo-channels. It makes use of a range of mineralogical compositions and particle size distributions for mineral dust as well as different crystal shapes and size distributions for ice clouds. With this information optical depth is also transferred to the traditional AOD wavelength of 550nm. As terrestrial infrared spectral variability information is used in the retrieval, it is sensitive to (silicate) dust particles only. The probabilistic brightness temperature difference approach allows for dust AOD retrieval also over desert surfaces with highly variable surface emissivity. As only observations of the 8-12µm range are used, the retrieval is independent of solar illumination, thus yielding dust observations twice daily. A pixel-wise retrieval error and dust probability are as well calculated. Validation results are documented in the Algorithm Theoretical Basis Document.The IMARS results also contain retrieved cloud information (optical depth, effective radius, ice water path, cloud top temperature).

Example result (June 01, 2008; descending orbits)



Satellite: Metop (EUMETSAT)
Instrument(s): IASI
Instrument/algorithm PI: Lars Klüser, DLR
Contact details: wdc[at]
Parameter(s): Mineral Dust AOD (0.55µm, 10µm), Effective Radius, Dust Mass Column, Dust Layer Temperature, Dust Mineralogy, Dust Probability
Aerosol algorithm: Infrared Mineral Aerosol Retrieval Scheme (IMARS)
Cloud screening: a posteriori probabilistic cloud screening
Aerosol model: four desert dust mixtures in three size distributions with nonspherical particles
Retrieval assumptions: neglible contribution of other aerosol types; external mixture of mineralogical components; dust concentrated in one single layer, clouds and dust vertically seperated, true mineralogy is represented by linear combination of assumked dust mixtures
Retrieval limitations: retrieval of AOD10µm and transfer to 0.5µm ; surface temperature may be underestimated from IASI observations; no explicit modelling of atmospheric moisture impact
Spatial, temporal coverage: 2007-2015 (processing ongoing in Aerosol_cci project),
Spatial, temporal resolution: 0.25° grid, 2200km swath / twice daily
Operations status: experimental
Validation status: evaluation against AERONET coarse mode AOD and comparison with other IASI products within ESA's Aerosol_cci project (
Quality control: pixel-wise intrinsic retrieval error, spectral corelation, a priori dust probability based on spectral correlation, pixel-wise quality flags
last algorithm version: 5.2 (01/2017)
last validation: 01/2017



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