Daily Aerosol Optical Depth and type over Europe from AATSR/SCIAMACHY
(ENVISAT)
Aerosol Retrieval Results at WDC-RSAT
Description and Product Example:
Synergetic aerosol optical depth and type: Map of aerosol optical depth
and type (as choice from 40 pre-defined representative mixtures) over
Europe (NRT) and global (offline) - data gaps are due to the SCIAMACHY
scanpattern (nadir-limb switching) and clouds (cover > 50%)
| Daily Aerosol Optical Depth at 550nm | Daily Aerosol Type |
|
 |
| Image Archive | Image Archive |
Fig. 1: SYNAER/ENVISAT 1-day overview maps of AOD and type over Europe and Africa for the last day processed. Retrieved boundary layer optical depth at 550 nm is shown in the left part. Retrieved AOD of four basic aerosol components (depicted as percentage of the pixel area) are shown in the right. Cloud covered SCIAMACHY pixels above 50% cloud fraction and pixels with a fit error larger than 0.01 (equivalent to 5% noise) are excluded. The image includes the orbits which are currently acquired in near-real time. Correction of SCIAMACHY radiometric errors in the level 1 product is done with a dynamical correction with simultaneous AATSR reflectances.
| Description & Product Example | |
| Synergetic aerosol optical depth and type | |
 |
 |
| Image Archive | Image Archive |
Fig. 2: showing the full dayside
orbits of the same day as in figure 1 over Europe and Africa.
see a HDF
explanation
In addition to orbits covering Europe and Africa (which can be seen in the quicklooks)
the HDF data archive and HDF latest day directory include also orbits covering
Asia (starting 15 August 2005).
The archive currently covers following data periods:
- latest day processed
- 15/6/2005 - current with some gaps (ENVISAT: Europe and Africa; Asia after 15/8/2005)
- 7/1997 - 8/1998 (ERS-2: Europe and Africa); 3 days each month due to GOME scan pattern
- reprocessing of 7/2003 - 12/2003 (Europe and Africa) will commence in September 2005
Aerosol parameters are retrieved with the new
method SYNAER [SYNergetic Aerosol Retrieval; Holzer-Popp et al., 2000, 2002a,
2002b] from a combination of simultaneous AATSR and SCIAMACHY measurements.
The high spectral resolution of SCIAMACHY ideally supplements the high spatial
resolution of AATSR. In this method cloud detection is first performed for all
1km AATSR pixels. Secondly, dark fields (dark vegetation, water bodies) are
selected automatically from the data itself in the 1.6 µm and 3.7 µm
channels and from the Normalized Difference Vegetation Index (NDVI) calculated
with the 670 and 870 nm channels. Then boundary layer aerosol optical depth
(BLAOT) values at 670 nm (over land) and 870 nm (over ocean) are derived for
these dark AATSR 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 AATSR 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 AATSR
derived parameters are co-registered to SCIAMACHY pixels and interpolated spatially.
BLAOT and surface albedo calculation is repeated for 40 different aerosol mixtures (see table 1) which are defined by external mixing of five basic aerosol components from an extended OPAC database (Hess et al., 1998). Using the AATSR calculated values of optical depth and surface albedo, SCIAMACHY surface and consecutively top-of-the-atmosphere spectra for the same set of different mixtures are simulated at 10 selected wavelengths. The measured SCIAMACHY spectra are corrected for cloud and ozone influence as well as radiometric errors. A least square fit of the simulated to the measured SCIAMACHY spectrum selects the most plausible type of aerosol and its corresponding BLAOT value at the reference wavelength of 550 nm in a SCIAMACHY 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 of the methodology applied to predecessor instruments GOME and ATSR-2 onboard ERS-2 showed proof of the SYNAER capabilities (error of optical depth below 0.06 at 670 nm and below 0.09 at 440 nm 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). Details of the aerosol model as described in Holzer-Popp et al. 2002a have been adjusted to recent observational findings (particularily more differentiation in absorption features of minerals and soot; see Holzer-Popp and Schroedter-Homscheidt, 2004a).
For questions please contact Thomas Holzer-Popp and Marion Schroedter-Homscheidt at DLR.
A case study validation against ground-based AERONET sun photometer measurements was conducted with ERS-2 GOME and ATSR-2 sensors (Holzer-Popp et al., 2002b). Furthermore an inter-comparison to other satellite aerosol optical thickness retrievals over ocean has been conducted (Myhre et al., 2005). Both give proof of the capability to derive accurate aerosol optical depth values better than 0.09 in the UV and better than 0.06 in the near infrared. SYNAER-ENVISAT version 2.0 was validated recently against 39 AERONET stations (Holzer-Popp, et al., 2008) and showed a bias near 0, standard deviations of 0.13 (0.10, 0.09) and correlations of 0.85 (0.85, 0.80) at 440 (550, 670) nm.
Fig. 3:SYNAER/ERS-2 case study validation
result showing inter-comparison to AERONET ground-based sun photometer observations
of spectral aerosol optical depth at 15 globally distributed sites.
Fig. 4: SYNAER/ENV validation
result showing inter-comparison to AERONET ground-based sun photometer observations
of spectral aerosol optical depth at 39 globally distributed sites.
Climate and atmospheric research; energy meteorology consultants (available direct/diffuse illumination for planning of renewable energy power plants), air quality monitoring. 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.
Data availability:
Operational provision of the daily SYNAER ENVISAT aerosol results has started 15/06/2005; a rolling archive is made available from this site (see HDF data and image link above). Results over Europe and Africa are provided in near-real time if both the necessary AATSR and SCIAMACHY level1 input files are available from ESA ftp site; global results will be produced 4-6 weeks after data acquisition. Reprocessing of ENVISAT data back to mid-2002 and the derivation of a 25 year aerosol climatology (1995-2020) with SYNAER applied to similar sensor pairs onboard ERS-2, ENVISAT and METOP is planned.
Precursor example results and future potential derived products:
Precursor results from ERS-2 (including a 1-km aerosol optical thickness) can be seen here. Furthermore, weekly composite maps, monthly mean and climatological datasets will be produced from this product; an example of a first 14-month ERS-2 based climatology over Europe and Africa can be seen here; a data file example in HDF4 format for the ERS-2 14-month climatology dataset can be found here. In synergy with external information on the vertical aerosol layering from models or lidar the conversion of the SYNAER retrieved aerosol optical thickness and type into near surface particle concentration maps (PM10, PM2.5, PM0.5) is planned; examples are discussed in Holzer-Popp and Schroedter, 2004b and can be seen here.
Hess, M., Köpke, P., Schult, I., Optical Properties of Aerosols and Clouds: The Software package OPAC, Bulletin of the Americal Meteorological Society, 79, pp. 831-844, 1998.
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, 2002a.
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, 2002b.
Holzer-Popp, T., Schroedter-Homscheidt, M., Satellite-based background concentration maps of different particle classes in the atmosphere, in: C. A. Brebbia, (eds.), Air Pollution XIII, WIT Press, Southampton, 2004b.
Holzer-Popp T., Schroedter-Homscheidt, M., Breitkreuz, H., Klüser, L., Martynenko, D., Synergistic aerosol retrieval from SCIAMACHY and AATSR onboard ENVISAT, Atmospheric Chemistry and Physics Discussions, 8, 1-49, 2008.
Holzer-Popp T., Schroedter-Homscheidt, M., Breitkreuz, H., Klüser, L., Martynenko, D., Improvements of synergetic aerosol retrieval for ENVISAT, Atmospheric Chemistry and Physics, 8, 7651-7672, 2008
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.
Myhre, G., Stordal, F., Johnsrud, M., Diner, D. J., Geogdzhayev, I. V., Haywood, J. M., Holben, B., Holzer-Popp, T., Ignatov, A., Kahn, R., Kaufman, Y. J., Loeb, N., Martonchik, J., Mishchenko, M. I., Nalli, N. R., Remer, L. A., Schroedter-Homscheidt, M., Tanre, D., Torres, O., Wang, M., Intercomparison of satellite retrieved aerosol optical depth over ocean during the period September 1997 to December 2000, Atmospheric Chemistry and Physics, 5, 1697-1719, 2005.
Popp, Th., Correcting atmospheric masking to retrieve the spectral albedo of land surfaces from satellite, Int. J. Rem Sens., 16, 3483-3508, 1995.
