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An improved equation for the radio refractive index of air
Author(s) -
Thayer Gordon D.
Publication year - 1974
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/rs009i010p00803
Subject(s) - refractive index , water vapor , partial pressure , ideal gas law , vapor pressure , atmospheric pressure , compressibility , humidity , vapour pressure of water , inverse , materials science , thermodynamics , physics , analytical chemistry (journal) , computational physics , chemistry , optics , mathematics , meteorology , geometry , quantum mechanics , oxygen , chromatography
New constants are derived for the equation relating the radio refractive index, n , at frequencies below 20 GHz to the pressure, temperature, and humidity of the air. The new equation is( n ‐ 1 ) × 10 6 = N = 77.6 (P a / T ) Z a ‐ 1 + 64.8 ( e / T ) Z w ‐ 1 + 3.776 × 10 5 ( e / T 2) Z w ‐ 1where P α is the partial pressure of dry air (mb), T is the absolute temperature (K), e is the partial pressure of water vapor (mb), and Z α −1 and Z w −1 are the inverse compressibility factors for dry air and water vapor, respectively. Improved values of the constants are obtained by considering the relationship between the radio and optical portions of the electromagnetic spectrum. With the use of the full three‐term equation including non‐ideal gas law effects, the accuracy of the new radio refractive index equation ranges from 0.018%, or about 0.05 N , for dry air to 0.048%, or 0.21 N , for extremely moist air.