Data & Products
Missions & Sensors
Daily total water vapour column over Europe and Africa from MSG/SEVIRI
Total water vapour column from SEVIRI at WDC-RSAT
Description and Product example:
The new TWC algorithm was tested with MSG-SEVIRI data for European and African regions for the period March - August 2004 and compared with radiosonde data. The results show that the algorithm is capable of producing TWC values with a mean bias of -0.2 mm and a RMSE of 6.8 mm (Fig. 2). From the total amount of 2583 coincidences for all viewing zenith angles both for winter and summer conditions, 82 % were within a ± 5 mm and 94 % were within a ± 10 mm difference interval between MSG-based and radiosonde-based TWC.
This RMSE value was very close to the accuracy range of 4 to 7 mm inherent in the radiosonde data set itself, which was assessed with a semi-variogram analysis. Therefore, we assumed that the observed scatter in satellite based TWC values versus radiosonde based TWC values is due to comparing two data sets with nearly comparable accuracy. Further analysis revealed neither a significant seasonal dependence in relative TWC errors nor a latitudinal structure within the comparison data set. Also, no significant dependence on air temperature profile characteristics was found.
A second comparison with European GPS TWC measurements reveals the best agreement with the 11 UTC measurement with a bias of -3.0 mm and a RMSE of 6.0 mm (Fig. 3). Two-hourly GPS measurements allow also for comparison of the cloud-free GPS-based daily mean value with the MSG-based TWC resulting in a bias of -2.6 mm and a RMSE of 6.8 mm. Comparison with GPS measurements shows also that large differences up to 20 mm canoccur in higher latitudes above 50° N in Europe. It is assumed that these cases can be attributed to failures in the cloud clearing procedure in cases with both large sun and satellite zenith angles.
A retrieval method for daily TWC measurements was elaborated which is accurate enough to be used for surface irradiance calculations in atmospheric correction and solar energy applications. The algorithm can be used in near-real-time operations without needing access to a numerical weather model output as a priori information. The restrictions to cloud-free regions are acceptable for these applications, as in case of clouds the cloud itself is the dominating element influencing surface irradiance. Also, the restriction to land surfaces is acceptable as solar energy power plants are currently not foreseen to be installed offshore.
Currently, daily data and quicklooks from 2004 and 2005 are available here.
A major reprocessing is ongoing and data can be made available in future.
For questions and more information please contact the SEVIRI team at DLR
Kleespies, J.T., McMillin L.M. (1990). Retrieval of precipitable water from observations in the Split Window over varying surface temperatures. Journal of Applied Meteorology, 29, 851-862
Schroedter-Homscheidt, M., A. Drews, S. Heise (2007) Total water vapor column retrieval from MSG-SEVIRI split window measurements exploiting the daily cycle of land surface temperatures, Remote Sensing of Environment, 249–258, doi: 10.1016/j.rse.2007.05.006 [pdf]