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Open AccessArticle

Assessment of Sampling Effects on Various Satellite-Derived Integrated Water Vapor Datasets Using GPS Measurements in Germany as Reference

1
Institute for Space Sciences, Freie Universität Berlin (FUB), Carl-Heinrich-Becker-Weg 6-10, 12165 Berlin, Germany
2
Institute for Geophysics and Meteorology, University of Cologne, Pohligstraße 3, 50969 Cologne, Germany
3
Helmholtz-Zentrum Potsdam—Deutsches GeoForschungsZentrum, Telegrafenberg, 14473 Potsdam, Germany
4
EUMETSAT, Eumetsat Allee 1, 64295 Darmstadt, Germany
*
Author to whom correspondence should be addressed.
Affiliation at the time this research was completed.
Remote Sens. 2020, 12(7), 1170; https://doi.org/10.3390/rs12071170
Received: 9 March 2020 / Revised: 31 March 2020 / Accepted: 2 April 2020 / Published: 6 April 2020
(This article belongs to the Special Issue Remote Sensing of Atmospheric Components and Water Vapor)
Passive imagers on polar-orbiting satellites provide long-term, accurate integrated water vapor (IWV) data sets. However, these climatologies are affected by sampling biases. In Germany, a dense Global Navigation Satellite System network provides accurate IWV measurements not limited by weather conditions and with high temporal resolution. Therefore, they serve as a reference to assess the quality and sampling issues of IWV products from multiple satellite instruments that show different orbital and instrument characteristics. A direct pairwise comparison between one year of IWV data from GPS and satellite instruments reveals overall biases (in kg/m 2 ) of 1.77, 1.36, 1.11, and −0.31 for IASI, MIRS, MODIS, and MODIS-FUB, respectively. Computed monthly means show similar behaviors. No significant impact of averaging time and the low temporal sampling on aggregated satellite IWV data is found, mostly related to the noisy weather conditions in the German domain. In combination with SEVIRI cloud coverage, a change of shape of IWV frequency distributions towards a bi-modal distribution and loss of high IWV values are observed when limiting cases to daytime and clear sky. Overall, sampling affects mean IWV values only marginally, which are rather dominated by the overall retrieval bias, but can lead to significant changes in IWV frequency distributions. View Full-Text
Keywords: water vapor retrievals; validation; sampling effects; MODIS; MIRS; IASI; GPS water vapor retrievals; validation; sampling effects; MODIS; MIRS; IASI; GPS
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Carbajal Henken, C.; Dirks, L.; Steinke, S.; Diedrich, H.; August, T.; Crewell, S. Assessment of Sampling Effects on Various Satellite-Derived Integrated Water Vapor Datasets Using GPS Measurements in Germany as Reference. Remote Sens. 2020, 12, 1170.

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