An update on the synergetic aerosol retrieval

Abstract

At DLR-DFD a synergetic aerosol retrieval method SYNAER was developed (Holzer-Popp et al., JGR, 107, 2002), which exploits the complementary information content of the radiometer AATSR and the spectrometer SCIAMACHY, both onboard ENVISAT. This combination of two instruments allows to retrieve aerosol optical depth at 550 nm and aerosol speciation from a choice of pre-defined aerosol types. In the meantime, 3 years of ENVISAT AATSR and SCIAMACHY level 1 nadir data have been acquired (2003-2005). Processing of these data over the MSG field of view (Europe, Africa, Atlantic) has been started within the ESA GSE project PROMOTE, where SYNAER contributes to the air quality monitoring service. SYNAER products are provided daily in near-real time since June 2005 as input for data assimilation into chemistry transport models, and as long-term evolving archive. Furthermore, first examples of converting SYNAER AOD and aerosol type into near-surface particulate matter concentrations and assimilation into the EURAD chemistry-transport model to improve the treatment of episodic emission patterns have been achieved. Validation of these SYNAER results is an ongoing activity. The validation efforts so far showed the potential to estimate the aerosol type from space (AOD error around 0.1 from UV to NIR, which is in perfect match with the expected noise level for the exploited pixel size), but also revealed cases of large AOD errors. Suspected reasons for these are surfaces with higher albedo and cases, where the sun-photometer observation is not representative for the satellite pixel of 60x30km2. Several parts of the retrieval methodology have therefore been assessed in more detail to better understand these issues. This includes a stringent analysis of the information content for different surface-atmosphere conditions and illuminations (up to 3 degrees of freedom for the type of aerosol). Furthermore, an investigation of airborne surface spectra was conducted to improve the dark field treatment based on characterizing the 670nm surface albedo from 1.6 micron channel reflectance and vegetation index. Preliminary results of this refinement effort will be summarized and discussed. The mid-term perspective for the SYNAER products promises a long-term dataset ranging from 1995 with ERS-2 (ATSR-2 and GOME) to 2020 with METOP (AVHRR and GOME-2), as the algorithm development was always focused on applicability to all these 3 platforms (thus not using special features as e.g. SCIAMACHY mid infrared channels or ATSR dual view). This presentation summarizes the status of the activity ―Derivation of aerosol composition from space‖ as a contribution to subproject ACCENT-TROPOSAT-2 (AT2), Task Group 1 (and 2).