Synergetic use of microwave radiometer and multifilter rotating shadowband radiometer observations for the validation of satellite cloud retrievals
Abstract
Bi-spectral algorithms to estimate cloud properties from reflected solar radiation at an absorbing and a non-absorbing wavelength are routinely applied to observations of meteorological satellite imagers. The underlying inversion process is highly underconstrained, and is based on the simplified view of 1D radiative transfer theory. It is therefore difficult to quantify the overall accuracy of these retrievals, and validation with independent datasets is crucial. The combination of measurements from a multifilter rotating shadowband radiometer and a passive microwave radiometer allows us to obtain a simultaneous and independent estimate of cloud optical thickness, liquid water path and effective droplet size from surface observations. In this study, a comparison of the surface-derived time series of these cloud properties for two European sites is carried out with collocated and synchronised retrievals from the geostationary METEOSAT SEVIRI satellite imager. This is done in order to test the suitability of this approach for routine quality monitoring of the cloud property products generated by the Satellite Application Facility on Climate Monitoring (CM-SAF). A discussion of the uncertainties affecting the surface and satellite algorithm is given. Particular attention is paid to the spatial and temporal matching of measurements. Also, the effects of cloud variability and the different resolution scales of the instruments are studied. This allows us to assess the level of agreement of the individual time series under specific conditions. It is shown that validation statistics are highly sensitive to quality screening and case selection, as well as the spatial and temporal averaging scales used for the comparison. This finding highlights the necessity to quantify the effects of sensor resolution and variability on cloud datasets, and to develop standard procedures to be able to compare validation results for different retrieval algorithms and satellite platforms.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.A54C..01D
- Keywords:
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- 0321 ATMOSPHERIC COMPOSITION AND STRUCTURE / Cloud/radiation interaction;
- 3311 ATMOSPHERIC PROCESSES / Clouds and aerosols