Satellite Validation using Ground-based Spectroscopic Techniques

The major contribution to TROPOSAT from Chalmers is to participate in the development of validation strategies for tropospheric satellite data products. Since 1994 the group has been operating a ground-based high resolution Fourier transform spectrometer for solar spectroscopic measurements at the Harestua site (60 °N, 11 °E) in southern Norway. Since 1996 the activity has been part of the global network NDSC. The work involves development of optimal strategies for comparing total columns and profiles from satellites with corresponding entities derived from ground based FTIR spectra, hereby taking into account the different vertical resolution, averaging kernels and viewing geometries of the two techniques, and focusing on the troposphere. During the time frame of TROPOSAT ground based high resolution solar FTIR has successfully been applied to retrieve atmospheric columns of HCl, HF, O₃ and CH₄ and we are presently working on CO. We have also actively participated in measurements for satellite validation related to the satellites MOPITT, ODIN and ENVISAT. During 2001 and 2002 a total of about 100 measurement days with high quality data has been obtained. So far no official validation results are available, partly due to problems with the satellite retrieval algorithms, partly problems with the ground-based algorithms.In a second approach, a strategy for satellite and model validation is being developed based on a mobile solar UV-visible/IR system. Direct and scattered sunlight is being used to derive total columns of tropospheric molecules on a grid-size comparable to the one obtained from satellites and used in GCM models. Such a mobile solar UV-visible/IR system has been developed and successfully tested for measurements of industrial emissions, emissions from ship traffic and volcanic gas plumes. It was also used on a field campaign in Italy in an EU project aimed at satellite validation of formaldehyde. These data are presently in the process of being evaluated. An additional, very compact, system has been developed utilising scattered sunlight. This system has been applied in measurements of volcanic SO₂ emissions from a large number of volcanoes in Europe, the West Indies and central America.