8 



RADIO REFRACTIVE INDEX OF AIR 



Another set of values in common use is that of Essen and Froome (11) 

 which is listed in table 1.3 along with values determined by several other 

 authors. Subsequent microwave refractometer determinations of these 

 constants by Saito [14] in Japan yielded a value of Ki lower than that of 

 either Smith and Weintraub or of Essen and Froome and nearer to Grain's 

 determination. Saito's values of Ko and K^ lie between those of Smith 

 and Weintraub, and Essen and Froome. A recent French microwave 

 determination of these constants by Battaglie, Boudouris, and Gozzini 

 [15], has found the Smith and Weintraub values of Ki, Ko, and K^ given 

 by (1.16) fit their experimental data within measurement error. The use 

 of the Essen and Froome values in radio geodesy appears to be based 

 upon Wadley's [16] comparison of optical and radio surveys and his con- 

 clusion that the best (radio) consistency is obtained when using Essen 

 and Froome's constants in conjunction with their determination of the 

 velocity of light. 



Table 1.3. Table of constants used by different authors 



Pd e e 



N = {n - I) 10« = A'l — + K.- + Kz — 



Reference 



Schelleng, Burrows, and Ferrell [20] 



Englund, Crawford, and Mumford [41] 



Waynick [35] 



Smith- Rose and Stickland [36] 



Burrows and Attwood NRDC [37] 



Meteorol. Factors in Prop. [40] 



Grain [10] 



Craig etal. [32] 



Essen and Froome [11] 



Smith and Weintraub [4] 



Essen [38] 



Saito [14] 



Battaglia, Boudouris, and Gozzini [15]. 

 Magee and Grain [42] 



Date 



1933 

 1935 

 1940 

 1943 

 1946 

 1946 

 1948 

 1951 

 1951 

 1952 

 1953 

 1955 

 1957 

 1958 



Ki 



79.0 



79.1 



79.0 



79.0 



79.0 



79.0 



77.10 



79.0 



77.64 



77.6 



77.26 

 77.6 



77.5 



Ki 



67.5 

 68.3 

 68.5 

 68.0 

 68.0 

 68.0 



(79) 

 64.68 

 72.0 

 75.0 

 67.5 

 72.0 

 65.0 



1.35 



3.81 



3.72 



3.8 



3.8 



3.8 



3.8 



3.718 



3.75 



3.68 



3.77 



3.75 



3.70 



The particular constants in the equation for A^ given by Smith and 

 Weintraub are considered to be good to 0.5 percent in N for frequencies 

 up to 30,000 Mc/s and normally encountered ranges of pressure, tempera- 

 ture, and humidity. Experimental determinations of the variability of 

 the radio refractivity, {n — 1)10^, with frequency have been carried out 

 by Essen and Froome [11] and are summarized in table 1.4. 



Remembering that the dispersion of refractive index would be expected 

 to be greatest at frequencies slightly off the water vapor resonance at 

 22 Gc/s and the oxygen resonance at 60 Gc/s [17] one concludes that for 

 the normally used frequencies, / < 30 Gc/s, the various gases give a 

 frequency variation of A^ well within the limits of accuracy given by Smith 



