Probing the Atmospheric Precipitable Water Vapor With SOFIA I + II + Tahiti
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Christian Fischer and Christof Iserlohe
Deutsche SOFIA Institut
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We report on measurements to determine the water vapor overburden, the dominant source of absorption of any far-infrared signal recorded from within the Earth's atmosphere, during SOFIA observations. These measurements are used to substantially improve the atmospheric calibration of far-infrared science data obtained with SOFIA. In part I of this talk we describe the measurement principle of telluric water vapor performed with the FIFI-LS instrument onboard SOFIA.  Since November 2018, these measurements are performed regularly with about 10 measurements per flight which created a large sample of data points at different geographical locations, flight altitudes and seasons, allowing some trend analysis. This presents the first systematic analysis of the water vapor in the stratosphere measured in situ with SOFIA. In part II of this talk we present a correlation of those measurements with atmospheric models provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). In fact, this correlation allows the determination of the water vapor overburden for each SOFIA flight from ECMWF data alone. The relative difference between the measured and modeled water vapor overburdens is of the order of about 10-20%. We finally present and discuss a statistical analysis of the water vapor overburden from ECMWF data which can be used for flight planning with a focus on southern deployments to Tahiti.

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