OMI Calibration and Validation Announcement of Opportunity

Executive Summary (from the Final Report)

Validation of the OMI total ozone column data products has benefited greatly from the OMI-AO activities. Extensive comparisons with ground-based data from the well established Dobson and Brewer network has revealed both splendid quality and opportunities for imporbvement of the OMI column ozone data products. OMI-DOAS total ozone columns are found to be ~1% higher than ground-based observations with a persistent dependence on solar zenith angle (SZA) and hence season. OMI-TOMS total ozone columns are found to have near-zero bias with the ground-based observations with no dependence on solar zenith angle or season. The SZA dependency has triggered retrieval improvements that, in combination with calibration updates, have largely removed this dependency. Details can be found in the contributions by Balis, Shavrina, and Weihs.

The OMI NO2 data product has been thoroughly analyzed under the OMI-AO banner. OMI NO2 total column observations are shown to compare well to almost three years of data recorded by ground-based FTIR instruments during sunrise. Modeling the diurnal cycle of stratospheric NO2 and propagating ground-based sunrise observations to the satellite overpass time strongly improves the comparison. Various contributions report on tropospheric NO2 observations in urban regions, under conditions that are challenging for satellite observations and satellite data retrievals. However, for air quality studies using satellite data this ground breaking work is vital. Details can be found in the contributions by Monks, Levelt, Richter, and Timofeyev. Interesting results of the DANDELIONS field campaigns are presented in this report.

The OMI surface-UV data product is again found to compare well with ground-based observations by, e.g., Brewer spectrometers and Jobin-Yvon spectroradiometer instruments. The issue of clouds and aerosols having an influence on ground-based and satellite based observations has been identified and is being investigated. Details can be found in the contributions by Tanskanen en Weihs, the latter report being explicitly composed of elaborate contributions from the teams collaborating within the project. Being an essential prerequisite for surface-UV validation, encouraging total ozone column validation results are also reported there.

The quality of the OMI aerosols data product has benefited greatly from the OMI-AO activities. Various studies provided feedback to the developers of the multi-wavelength aerosols retrieval algorithm. Although not included in the DANDELIONS final report, the pioneering work by Curier et al testing the retrieval over Western Europe should be mentioned here. The understanding of the of role aerosols in calculating air mass factors for trace gas retrievals significantly has increased and the effect of UV absorbing aerosols on surface-UV estimates from space is under investigation.

In general, correlative data sources for the remaining OMI operational data products, such as bromine oxide, chlorine dioxide, sulphur dioxide and formaldehyde are sparse. Fortunately, the OMI-AO hosts several PI’s operating ground-based instruments dedicated to measuring exactly these species. Results of comparing OMI and FTIR ground-based observations of formaldehyde columns are reported where the comparison is hindered by the large OMI footprint over mountainous Switzerland and the high altitude of the observatory. Details can be found in the contribution by Demoulin. Furthermore it is reported that, e.g., retrievals of ozone profiles by various techniques are readily available for comparisons. At the time of writing all OMI operational data products have been publically released and are available via the NASA DISC and NASA AVDC.

Validation results of OMI data products achieved under the OMI-AO banner have been presented at numerous international scientific meetings, e.g., European Geophysical Union meetings in Vienna, the ENVISAT 2007 Montreux symposium, various OMI Science Team Meetings and Aura Science Team Meetings. Many papers reporting the validation work performed within the framework of the OMI AO have been published in the Journal of Geophysical Research (JGR) Atmospheres - Special Issue on EOS-Aura validation. Various toher papers have been published elsewhere in high quality peer-reviewed journals and their literature references are cited in this final report and the end of the individual chapters.

The outcome of the OMI AO Questionnaire is very encouraging, not just for the organization of the activity, but also for the future prospect of organizing a similar opportunity for upcoming atmospheric missions in Europe.