Measurement of the refractive index of air and comparison with modified Edl n's formulae

Abstract

An air refractometer has been developed for accurate measurements of the refractive index of gases under well-defined conditions. Measurements have been performed for dry and moist air at four wavelengths distributed over the visible part of the spectrum. The measured values have been compared with values determined by modified Edlén's formulae and measured parameters. A fitting procedure is described to adjust the humidity dependence and the constant term of the dispersion formula so that optimum agreement is obtained. A standard deviation of 3 10 -9 for the residuals describes the reproducibility of the measurements and the success of fitting. For 50 % relative humidity, a standard uncertainty of 10 -8 for the fitted formulae is claimed, arising mainly from the uncertainty contributions of the air parameters.

Refractive index of humid air in the infrared: model fits

“…The relative deviation of 6 × 10 −3 between experiment and theory is still compatible with the error 5 × 10 −3 provided by Marchetti and Simili. The theory deviates from the humid air data at the longest two wavelengths of the Bönsch-Potulski experiments [9] by 3.5 × 10 −8 or less: Fig. 3.…”

“…experiments on moist air in the visible [3,9,18,53], 2. experiments on pure water vapor at 3. 4 and 10.6 µm [44,48,49], 3.…”

“…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. Since we will not present these functions at high resolution but smooth fits within several bands in the infrared, their spiky appearance sets a natural limit to the far-IR wavelength regions that our approach may cover.…”

Greenhouse gas profiling by infrared-laser and microwave occultation: retrieval algorithm and demonstration results from end-to-end simulations

“…Schweitzer et al, 2011b) and an ellipsoidal Earth shape (WGS84, Fuchs and Stoffel, 1984). The ray-tracing uses for the LMO channels the microwave refractivity formula of Smith and Weintraub (1953) and for the LIO channels an accurate but simplified approximation of the visible/infrared refractivity formula by Bönsch and Potulski (1998) (more details in Sect. 3.3).…”

“…Figure 1 illustrates the LMO and LIO signal propagation paths, with all signals transmitted from one joint platform, LEO Tx , and received at another joint platform, LEO Rx . Both LMO and LIO signals follow closely similar but not identical paths, i.e., the refraction becomes somewhat different for the microwave (MW) and infrared (IR) signals, proportional to the amount of water vapor in the air (Thayer, 1974;Bönsch and Potulski, 1998;Kirchengast and Schweitzer, 2011;Schweitzer et al, 2011a). The corresponding difference in bending of MW and IR ray paths is practically negligible above about 8 km to 12 km, a highly favorable property, and gradually increases downwards into the troposphere (Schweitzer et al, 2011a), leading to a difference of the tangent altitudes of about 0.5 km near 5 km in moist conditions (Kirchengast et al, 2010a).…”