An empirical study on the importance of a speed-dependent Voigt line shape model for tropospheric water vapor profile remote sensing

We use high quality ground-based solar absorption spectra measured in close coincidence with Vaisala RS92 radiosonde in situ water vapor profiles to demonstrate that a Voigt line shape model yields systematic errors in the remotely sensed tropospheric water vapor profiles. We analyse absorption signatures of 4 H216O and 2 HD16O bands situated between 790 and 4710 cm−1. We find that applying a speed-dependent Voigt line shape model instead of a Voigt line shape model significantly improves the agreement between the water vapor profiles obtained by the radiosondes and by infrared remote-sensing in the different bands. An optimal agreement is obtained for a Γ2 (relaxation rate for speed-dependence) of 6-21% of Γ0 (Voigt relaxation rate), which is consistent to the values derived from laboratory experiments. Our study suggests that further extensive laboratory investigations of line shape models are a key for improving the quality of modern water vapor remote sensing products.

Research Highlights► Line-shapes are very important for modern infrared remote sensing. ► Investigation of infrared water vapor line-shapes beyond the Voigt line-shape. ► Voigt versus speed-dependent Voigt line-shape model. ► Relaxation rate for speed-dependence parameters for different bands.