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Abstract
The MERIS spectrometer on board of the ENVISAT satellite obtains Integrated Water Vapor (IWV) estimates in swaths of 1150 km at unprecedented spatial resolutions of up to 300m. As ENVISAT also carries the ASAR instrument and is only separated by 30 minutes from the ERS-2 SAR instrument, MERIS IWV has potential to assess the impact of water vapor on both ERS-2 and ASAR data. Unfortunately, MERIS only gives reliable IWV estimates under clear sky conditions. For a country as The Netherlands, this implies that more than 50 percent of the MERIS IWV pixels is lost. To correct for this loss it is proposed to fill gaps in MERIS IWV scenes using GPS IWV observations as available from GPS ground stations.
Cloud gaps will be filled using two types of information: I) by MERIS IWV observations from around the gaps, and II) by co-temporal GPS IWV observations, available at about each 20 km as processed by the KNMI. The weighting between the GPS and MERIS IWV observations will be based on Co-Kriging. To validate the quality of the filled pixels, a completely independent data source is used. Coherent SAR images allow the estimation of high quality, high resolution water vapor interferogram data. The validation procedure will not only be used to assess the new filling approach, but also special attention will be paid to the method of cloud masking, as this is expected to have high impact on the quality of the final repaired MERIS IWV scenes.