Van Geffen, J., Van Roozendaal, M., Rix, M. and Valks, P.: 2008,
BIRA-IASB/DLR technical note TN-IASB-GOME2-O3MSAF-SO2-01, September 2008.
The aim of the present document is first to report on the status of the verification of the GOME-2 SO2 column against a synchronised scientific algorithm available at BIRA. For this exercise, SO2 retrieval settings selected by DLR scientists for GDP version 4.2 are being used. The consistency of this SO2 product is then explored by performing various comparisons with SO2 column data determined from measurements of satellite-based instruments SCIAMACHY and OMI, as well as selected ground-based instruments. Ground-based SO2 column measurements available for volcanic eruptions (Kasatochi) and anthropogenic pollution (Beijing) are also used in an attempt to further document the geophysical consistency of the GOME-2 SO2 product.
It should be noted here that validation of satellite-based SO2 data products has not been done in any systematic way so far: the validation carried out so far is limited, because of the difficulties involved in comparisons between ground-based and satellite-based data, as well as difficulties in the comparison of the data from different satellites. These difficulties are, for example, related to measuring different air masses at different moment of the day. There have been some preliminary comparisons of OMI SO2 data against in-situ aircraft measurements over NE China [Krotkov et al., 2008], and in-situ ground-based measurements at some stations in China has been compared against SCIAMACHY and OMI data [Zhang et al., 2008]. Additional validation exercises both in-site vs. satellite comparisons and satellite inter-comparisons are part of several projects related to monitoring of volcanic or anthropogenic SO2 emissions; results of these comparisons are not published yet. The validation results presented here must be considered as preliminary and therefore subject to possible revisions.
Reported validation studies were carried out at the Belgian Institute for Space Aeronomy (BIRA-IASB, Brussels, Belgium) and at DLR Remote Sensing Technology Institute (DLR-IMF, Oberpfaffenhofen, Germany) in the framework of EUMETSAT Satellite Application Facility on Ozone and Atmospheric Chemistry Monitoring (O3M-SAF).
A. Introduction A.1. Scope of this document A.2. Preliminary notes A.3. Plan of this document B. Settings for SO2 column retrieval from GOME-2 B.1. Experience from ERS-2/GOME and SCIAMACHY B.2. Choice of SO2 slant column settings for GOME-2 C. Verification of SO2 slant columns and sensitivity tests D. Comparison against satellite data D.1. Assumed elevation of the SO2 in the atmosphere D.2. Comparison of volcanic SO2 in the stratosphere D.3. Comparison of volcanic SO2 in the mid-troposphere D.4. Comparison of anthropogenic SO2 in the lower troposphere E. Comparison against GROUND-based Measurements E.1. Ground-based instruments used for the comparisons E.2. Satellite data used for the comparisons E.3. Anthropogenic SO2 total columns measured in Beijing E.4. The passing of volcanic SO2 over ground stations in Uccle and Manchester F. Conclusion G. ReferencesPDF file of the report (28; 1.4 MB)
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