Abstract
Water vapor fluxes play a key role in the energy budget of the atmosphere, and better flux measurements are needed to improve our understanding of the formation of clouds and storms. Large-scale measurements of these fluxes are possible by employing the eddy correlation (EC) method from an aircraft. A hygrometer used for such measurements needs to deliver a temporal resolution of at least 10 Hz while reliably operating in the harsh conditions on the exterior of an aircraft. Here, we present a design concept for a calibration-free, first-principles, open-path dTDLAS hygrometer with a planar, circular and rotationally symmetric multipass cell with new, angled coupling optics. From our measurements, the uncertainty of the instrument is estimated to be below 4.5% (coverage factor k = 1). A static intercomparison between a dTDLAS prototype of the new optics setup and a traceable dew point mirror hygrometer was conducted and showed a systematic relative deviation of 2.6% with a maximal relative error of 2.2%. Combined with a precision of around 1 ppm H2O at tropospheric conditions, the newly designed setup fulfills the static precision and accuracy requirements of the proposed airborne EC hygrometer.
Highlights
Water vapor is the most important greenhouse gas, and plays a key role in the energy budget of the atmosphere [1]
The eddy correlation (EC) method can be used to measure these fluxes by correlating the vertical component of the wind vector with fast and accurate H2 O concentration values [3]
This method is commonly used in stationary setups, such as meteorological EC flux towers, to determine the water vapor flux from the ground into the atmosphere at one specific location [4,5]
Summary
Water vapor is the most important greenhouse gas, and plays a key role in the energy budget of the atmosphere [1]. The eddy correlation (EC) method can be used to measure these fluxes by correlating the vertical component of the wind vector with fast and accurate H2 O concentration values [3] This method is commonly used in stationary setups, such as meteorological EC flux towers, to determine the water vapor flux from the ground into the atmosphere at one specific location [4,5]. The use of a closed- or open-path optical cell is one of the key characteristics of an airborne hygrometer. Notable instruments that utilize an extractive sampling and a closed-path cell on are [6,7,9,10,11,12,13,14,15,16,17].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
