1The Catholic University of America, 620 Michigan Ave., Washington D.C. 20064, USA
2NASA Goddard Space Flight Center, Mailcode 674, Greenbelt Rd., Greenbelt, MD 20771, USA
3GATS Inc., 1164 Canon Blvd., Suite 101, Newport News, VA 23606, USA
4Instituto de Astrofísica de Andalucía (CSIC), C/Camino Bajo de Huetor, 50, Granada 18008, Spain
5Institute for Physics, St. Petersburg State University, Ulianovskaja, 1, St. Petersburg, 198904, Russia
6La Trobe University, Victoria, 3086, Australia
7Hampton University, Hampton, VA 23668, USA
Abstract. This paper describes a methodology for water vapor retrieval using 6.6 μm daytime broadband emissions measured by SABER, the limb scanning infrared radiometer on board the TIMED satellite. Particular attention is given to accounting for the non-local thermodynamic equilibrium (non-LTE) nature of the H2O 6.6 μm emission in the mesosphere and lower thermosphere (MLT). The non-LTE H2O (ν2) vibrational level populations responsible for this emission depend on energy exchange processes within the H2O vibrational system as well as on interactions with vibrationally excited states of the O2, N2, and CO2 molecules. The paper analyzes current H2O non-LTE models and, based on comparisons with the ACE-FTS satellite solar occultation measurements, suggests an update to the rate coefficients of the three most important processes that affect the H2O(ν2) populations in the MLT: a) the vibrational-vibrational (V–V) exchange between the H2O and O2 molecules; b) the vibrational-translational (V–T) process of the O2(1) level quenching by collisions with atomic oxygen, and c) the V–T process of the H2O(010) level quenching by collisions with N2, O2, and O. We demonstrate that applying the updated H2O non-LTE model to the SABER radiances makes the retrieved H2O vertical profiles in 50–85 km region consistent with climatological data and model predictions.