Daily Aerosol Optical Thickness and type over Europe from ATSR-2/GOME (ERS-2), AATSR/SCIAMACHY (ENVISAT), AVHRR/GOME-s (METOP)

Description

1km gridded boundary layer aerosol optical thickness map and overview map of aerosol optical thickness and type (as choice from 40 pre-defined representative mixtures) over Europe

Product Examples:

Synergetic aerosol optical thickness and type

Fig. 1: SYNAER 3-day overview maps over Europe for 1. - 3. September 1995. Retrieved boundary layer optical thickness at 550 nm is shown in the left part ranging from 0.03 to 0.55. Retrieved percentage contributions of six basic aerosol components (depicted as percentage of the pixel area) are shown in the right (IN=insoluble, WA=watersoluble, SO=soot, SA=sea salt accumulation mode, SC=sea salt coarse mode, MT=mineral transported). Cloud covered GOME pixels above 50% cloud fraction are excluded. Pixels with large fit errors were excluded from both maps by the quality check. The ambiguity test was not applied

Fig. 2: High resolution aerosol optical thickness (AOT) map above Europe based on satellite measurements and using the SYNAER method. Shown is the AOT for the time period from 1. - 3. September 1995 based on measurements from ERS-2-GOME and ATSR.

Methodology:

Aerosol parameters are retrieved with the new method SYNAER [SYNergetic Aerosol Retrieval; Holzer-Popp et al., 2000, 2002a, 2002b] from a combination of simultaneous ATSR-2 and GOME measurements. The high spectral resolution of GOME ideally supplements the high spatial resolution of ATSR-2. In this method cloud detection is first performed for all ATSR-2 pixels. Secondly, dark fields (dark vegetation, water bodies) are selected automatically from the data itself in the 1.6 ?m and 3.7 ?m channels and from the Normalized Difference Vegetation Index (NDVI) calculated with the 670 and 870 nm channels. Then boundary layer aerosol optical thickness (BLAOT) values at 670 nm (over land) and 870 nm (over ocean) are derived for these dark ATSR-2 nadir pixels for which the surface albedo can be estimated with good accuracy. BLAOT values over the irregularly distributed dark fields are interpolated to all cloud free ATSR-2 pixels with a distance weighting scheme. Using the atmospheric correction scheme EXACT [Popp, 1995], which has been validated using Landsat-TM and NOAA-AVHRR data, the surface albedo values for the 3 wavelengths 560 nm, 670 nm and 870 nm are obtained for all cloud free pixels. The ATSR-2 derived parameters are co-registered to GOME pixels and interpolated spatially. BLAOT and surface albedo calculation is repeated for 40 different aerosol mixtures which are defined by external mixing of six basic aerosol components. Using the ATSR-2 calculated values of optical thickness and surface albedo, GOME surface and consecutively top-of-the-atmosphere spectra for the same set of different mixtures are simulated at 10 selected wavelengths. The measured GOME spectra are corrected for cloud and ozone influence. A least square fit of the simulated to the measured GOME spectrum selects the most plausible type of aerosol and its corresponding BLAOT value at the reference wavelength of 550 nm in a GOME pixel. Finally, a quality control and an ambiguity test are applied by comparing the fit error with deviations between different mixtures. A case study validation showed proof of the SYNAER capabilities (error of optical thickness at 550 nm below 0.1 and capacity to differentiate the type of aerosols between continental, maritime, polluted, desert outbreak and biomass burning / heavily polluted air masses as mixtures of 4 basic aerosol components (sulfate/nitrate, mineral dust, sea salt, soot).

For questions please contact Thomas Holzer-Popp and Marion Schroedter-Homscheidt at DLR.

Major users:

Climate and atmospheric research; energy meteorology consultants (available direct/diffuse illumination for planning of renewable energy power plants), air quality monitoring.

Relevance:

Assimilation of aerosol optical thickness (differentiated by major components) into atmospheric model to derive ground level PM distributions including episodic emissions from e. g. irregular fire events; indicator maps for heavy particle pollution.

Publications:

Holzer-Popp, T., M. Schroedter, and G., Gesell, Retrieving aerosol optical depth and type in the boundary layer over land and ocean from simultaneous GOME spectrometer and ATSR-2 radiometer measurements, 1, Method description J. Geophys. Res., 107, D24, 2002.

Holzer-Popp, T., M. Schroedter, and G., Gesell, Retrieving aerosol optical depth and type in the boundary layer over land and ocean from simultaneous GOME spectrometer and ATSR-2 radiometer measurements, 2, Case study application and validation, J. Geophys. Res., 107, D24, 2002.

Holzer-Popp, Th., Schroedter, M., Gesell, G., High Resolution Aerosol Maps Exploiting the Synergy of ATSR-2 and GOME, Earth Obs. Quarterly, 65, 19-24, 2000.
Popp, Th., Correcting atmospheric masking to retrieve the spectral albedo of land surfaces from satellite, Int. J. Rem Sens., 16, 3483-3508, 1995.