Calculated refractivity of water vapor and moist air in the atmospheric window at 10 μm

Abstract

The HITRAN 2000 database of infrared line transitions has been used to calculate the dispersion coefficient of water vapor at room temperature in the atmospheric window up to 25 microm, confirming an equivalent earlier compilation [Infrared Phys. 26, 371 (1986)]. I complement this line set by using an previously published ultraviolet pseudospectrum [J. Chem. Phys. 68, 1426 (1978)] to improve coverage of the near infrared. The effect of admixtures of abundant nitrogen, oxygen, and carbon dioxide is predicted on the same calculational basis to synthesize the air representative of the mountain that hosts the Very Large Telescope Interferometer and is found to be small compared with the dominant role of water at wavelengths above 3 microm.

Refractive index of humid air in the infrared: model fits

“…Line strengths S ml and positions ω 0ml are based on the HITRAN [60] list (see [68,69] for reviews) and other sources as described earlier [46]. The results of Section IV include summation over the oscillator strengths of the air components N 2 , O 2 , Ar, Ne, CO 2 , H 2 O, O 3 , CH 4 and CO. Fig.…”

“…1 is an estimate of the combined contribution of tracer gases that are missing in this mix of moleculesand effectively replaced by the average refractivity of the major components-sorted with respect to abundance under rather clean environmental conditions. Their electromagnetic line lists are taken from [41,75] for He, [11] for Kr, [45] for H 2 , [45,60] for N 2 O, [60] for SO 2 , and [45,60] The remaining subsections describe some refinements of the computer program relative to its status three years ago [46].…”

“…The approach is in continuation of earlier work [46] based on a more recent HITRAN database [60] plus more precise accounting of various electromagnetic effects for the dielectric response of dilute gases, as described below.…”

“…The paper provides easy access to predictions of the refractive index of humid air at conditions that are typical in atmospheric physics, in support of ray tracing [5] and astronomical applications [4,16,47,50] until experimental coverage of the infrared wavelengths might render these obsolete. The approach is in continuation of earlier work [46] based on a more recent HITRAN database [60] plus more precise accounting of various electromagnetic effects for the dielectric response of dilute gases, as described below.The literature of optical, chemical and atmospheric physics on the subject of the refractive index of moist air falls into several categories, sorted with respect to decreasing relevance (if relevance is measured by the closeness to experimental data and the degree of independence to the formalism employed here):1. experiments on moist air in the visible [3,9,18,53 [42,61,79] and eventually in the static limit [24], the refractive index plotted as a function of wavelength is more and more structured by individual lines.…”

“…The paper provides easy access to predictions of the refractive index of humid air at conditions that are typical in atmospheric physics, in support of ray tracing [5] and astronomical applications [4,16,47,50] until experimental coverage of the infrared wavelengths might render these obsolete. The approach is in continuation of earlier work [46] based on a more recent HITRAN database [60] plus more precise accounting of various electromagnetic effects for the dielectric response of dilute gases, as described below.…”