Quality assessment and improvement of the EUMETSAT Meteosat Surface Albedo Climate Data Record

[摘要] Surface albedo has been identified as an important parameter forunderstanding and quantifying the Earth's radiation budget. EUMETSATgenerated the Meteosat Surface Albedo (MSA) Climate Data Record (CDR)currently comprising up to 24 years (1982–2006) of continuoussurface albedo coverage for large areas of the Earth. This CDR hasbeen created within the Sustained, Coordinated Processing ofEnvironmental Satellite Data for Climate Monitoring (SCOPE-CM)framework. The long-term consistency of the MSA CDR is high and meetsthe Global Climate Observing System (GCOS) stability requirements fordesert reference sites. The limitation in quality due to non-removedclouds by the embedded cloud screening procedure is the most relevantweakness in the retrieval process. A twofold strategy is applied toefficiently improve the cloud detection and removal. The first stepconsists of the application of a robust and reliable cloud mask, takingadvantage of the information contained in the measurements of theinfrared and visible bands. Due to the limited information availablefrom old radiometers, some clouds can still remain undetected. A secondstep relies on a post-processing analysis of the albedo seasonalvariation together with the usage of a background albedo map in orderto detect and screen out such outliers. The usage of a reliable cloudmask has a double effect. It enhances the number of high-qualityretrievals for tropical forest areas sensed under low view angles andremoves the most frequently unrealistic retrievals on similar surfacessensed under high view angles. As expected, the usage of a cloud maskhas a negligible impact on desert areas where clear conditionsdominate. The exploitation of the albedo seasonal variation for cloudremoval has good potentialities but it needs to be carefullyaddressed. Nevertheless it is shown that the inclusion of cloudmasking and removal strategy is a key point for the generation of thenext MSA CDR release.

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