Determination of optical properties of desert dust aerosol for satellite validation - AERVAL

• Applicant: Professor Dr. John Philip Burrows
• Subject Area: Atmospheric Science
• Term: from 2004 to 2006
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5470891

This proposal will develop and validate a procedure for the retrieval of optical thickness of desert dust over arid land surfaces using multi-spectral, nadir-looking satellite radiometers. The retrieval algorithms generated will also be suitable for application to data from other relevant sensors. Using the validated inversion technique, the regional distribution of Top Of the Atmosphere (TOA) aerosol optical thickness (AOT) over desert regions will be estimated from relevant satellite data. The project establishes collaboration between scientists from Germany and Morocco and thereby contributes to the agreement on scientific cooperation between the DFG of the Bundesrepublik Deutschland and the CNR of the Kingdom of Morocco from 28. Oct. 1986. The global and national problem of desertification is the scientific issue to be addressed. (Support for Prof. M. Diouri and his co-workers at the University of Oujda is the subject of a separate and independent proposal. The success of DREAMS does not depend on this proposal being granted.) The retrieval of aerosol parameters from passive multi-spectral space-borne radiometers is an ill-posed mathematical problem. To retrieve reliable aerosol data products over land and water surfaces, a-priori knowledge of the aerosol and surface optical properties are required. The latter comprise the aerosol phase function, the single scattering albedo and the spectral surface reflectance. To achieve this objective retrieval algorithms typically compile so-called Look Up Tables by radiative transfer modeling. The scientific objective of this research project in its first phase (year 1-3) is the development and validation of a retrieval procedure to derive the optical thickness of desert dust over arid land surfaces BAER-D. To achieve this goal several specific tasks have to be undertaken: (1) The development of a model of spectral surface reflectance of dust source regions, (2) The determination of optical aerosol parameters for desert dust, (3) The calculation of look-up-tables using these aerosol properties for the retrieval of the aerosol optical thickness, (4) The validation of the data products by comparison with ground based measurements. The radiation closure experiment, planned within the joint research project, which will include ground-based measurements of aerosol optical parameters, the determination of vertical profile of the aerosol, the determination of the surface spectral reflectance from aircraft provides all required data for the development of the aerosol retrieval procedure for desert dust from satellite data. Such a procedure does not exist worldwide. In phase 2, (year 4-6) of DREAMS, applications of the BAER-D retrieval procedure to satellite data are planned. The main aim of the second phase within the overall project, which has a focus on dust transport, comprises the investigation of the predictive power of circulation and transport models and data retrieved from satellite measurements. The specific objectives are: (1) The comparison of model predictions of the transport of aerosol with regional distributions of AOT retrieved from satellite measurement along the trajectories, (2) The calculation of TOA-reflectance from model predictions of the AOT of desert dust and comparison with measured TOA reflectances of the satellite radiometers, (3) The estimation of the up-welling shortwave TOA-flux from TOA reflectances.

• DFG Programme: Research Units
• Subproject of: FOR 539: Saharan Mineral Dust Experiment SAMUM
• International Connection: Morocco
• Participating Persons: Professor Dr. Mohammed Diouri; Privatdozent Dr. Wolfgang von Hoyningen-Huene