## 1 Introduction  
Water vapor is the most abundant greenhouse gas and is routinely measured in atmospheric chemistry research [1; 2; 3]. Atmospheric water vapor measurements are often performed by instruments such as balloon radiosondes and satellite-based infrared sensors [1]. Throughout recent years, several studies both in the lab and in the field have been performed to improve the accuracy and reproducibility of water vapor amount fraction (concentration) measurements (employing a variety of hygrometers) [1; 2; 3; 4; 5; 6; 7; 8]. Studies in well-controlled environments comparing a wide variety of field hygrometers for atmospheric applications [1] have revealed large systematic discrepancies (about 10% and even larger in tropopause conditions) in the H\({}_{2}\)O concentration results. These discrepancies can be in part attributed to deficiencies in the measurements and the lack of SI-traceable hygrometer calibrations, in particular at the low concentration ranges [3]. Laser hygrometers, e.g., based on direct tunable diode laser absorption spectroscopy (dTDLAS), are increasingly used for the measurement of H\({}_{2}\)O in a broad range of applications [8; 9; 10; 11; 12; 13] such as airborne measurements [14], optical open path pressure measurements [9], tomographic 2-D water vapor measurements [15], high-resolution water transpiration rate measurements in single plant leaves [12] or for trace water measurements down to the nmol/mol level [13]. For spectroscopic H\({}_{2}\)O measurements, the H\({}_{2}\)O absorption line in the near infrared (NIR) at about 1.37 \(\upmu\)m (i.e., at 7299.43 cm\({}^{-1}\)) is almost ideal due to its good spectral isolation allowing simplified fitting schemes. Hence, this line is very frequently used in a multitude of applications and publications [8; 11; 12; 14; 15; 16]. The use of this 1.37 \(\upmu\)m H\({}_{2}\)O line originated from a dedicated line selection process and test measurements [3; 11; 17], as well as the availability of fairly low-cost (compared to the mid-infrared MIR) near-infrared optical elements and detectors from telecom mass applications that are hence easily available with excellent performance parameters. This is particularly true for the fiber-coupled diode lasers [13] that spurred the development of very compact field-compatible laser hygrometers [5; 11; 14]. In gas metrology, employing these 1.37 \(\upmu\)m laser hygrometers to realize the most accurate H\({}_{2}\)O amount fraction measurements at the same time requires accurate (metrology compatible) spectral line data (line strength, collisional broadening coefficients) for this H\({}_{2}\)O line at 7299.43 cm\({}^{-1}\). The curation of new improved line data will further improve the data quality of results delivered by a new generation of 1.37 \(\upmu\)m laser hygrometers that is envisaged. The idea of measuring metrology-compatible line data for gas species amount fraction measurements has been promoted for a variety of molecules in different applications [10; 18; 19; 20; 21]. The line data are used, e.g., in new lab- and field-based laser absorption spectrometers being developed to be operated as calibration-free optical gas standards (OGSs) [3; 7; 8; 11; 13; 14; 22; 23]. An OGS delivers direct SI-traceable gas species concentration results and can also complement gaseous calibration standards even at the \(\upmu\)mol/mol (ppm) level [3; 4; 22]. A prominent spectroscopy technique for such OGSs is direct tunable diode laser absorption spectroscopy (dTDLAS). It should be noted here, as also detailed in our previous works [3; 6; 7; 11; 14; 23; 24; 25], that dTDLAS is a variant of TDLAS that combines TDLAS with a special first principles data evaluation approach to directly extract absolute gas species concentrations without calibration of the spectrometer with gaseous reference standards.