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Generation of IASI/AVHRR Data SetIASI Sample ClassificationThe data set of IASI samples is derived by visual analysis of globally distributed data.The data set serves as input for the optimisation and validation of the IASI cloud detection. Based on the output of the IASI cloud detection tests, each collected IASI sample will be classified concerning its cloudiness as being a clear-sky, partly cloudy and cloudy footprint based on the visual inspection of the AVHRR pixels covered by an IASI footprint. In order to ensure the representativeness of the data-set for the natural variability of those parameters which affect the radiation measurement from a space borne instrument additional classification are performed for each IASI footprint:
CloudinessFor the assessment of the cloudiness of an IASI sample four cloud classes was used for the visual classification of the collected IASI samples:
 Surface Types The surface type database which was used as ancillary information in this project is the IGBP scene types in the CERES/SARB surface map. The data are freely available from
the IGBP Website or from
the MODIS Website.A technical description of the dataset, as it is used in the IAVISA tools is given in chapter IGBP Surface Type Map. The binary file IGBPa_1198.map was downloaded.
The web pages explain the use of the International Geosphere/Biosphere Programme (IGBP) scene types in the CERES/SARB surface map. The map below shows the 18surface types used by the SARB group to identify surface properties of a given region. Scene types were delineated by IGBP. This map is determined using a 1km IGBP scene types supplied by USGS. An 18th scene type (Tundra) is added to distinguish the rocky/barren scene of northern climes vs. that of other deserts. These scene types map the geographic region to long wave and shortwave spectral emissivity and albedo properties defined within the spectral ranges of the Fu & Liou Code. The spectral properties page has a complete description of data source. The distribution of the surface types in the map is as follows:
Climate Zones
Five major climatic types are recognized in this system, each type being designated by a capital letter:
No-data gaps in the Köppen map are filled by the software with Fallback values according to the following scheme based on the pixel’s latitude value.
SeasonsIn the context of the current study, climatological seasons are used. I.e., for the Northern hemisphere, spring begins by convention on 1 March, summer on 1 June, autumn on 1 September and winter on 1 December.
Day-Night classificationThe information about day or night condition during time of the measurement was taken from the Scene Meta data. If the sun zenith angle is below 90° a night measurement is assumed, a day measurement otherwise.
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clear - if the shape of the IASI footprint contains exclusively AVHHR pixels which are unambiguously cloud free, 28% of all cloudy samples,
partly cloudy low - if the shape of the IASI footprint contains both cloudy and cloud free AVHRR pixels, less than ~ 20% cloudy pixels, 26% of all cloudy samples ,
partly cloudy high - if the shape of the IASI footprint contains both cloudy and cloud free AVHRR pixels, more than ~ 20% cloudy pixels, 26% of all cloudy samples,
cloudy - if the shape of the IASI footprint contains exclusively AVHHR pixels which are unambiguously cloudy, 20% of all cloudy samples. 
