396 CHARTS, GRAPHS, TABLES, AND COMPUTATIONS 



Table 9.29. Parameters for exponential refraction with height for various values of k 



9.3. Refractivity Tables 



Tables 9.30 through 9.35 have been prepared on a digital computer to 

 assist the reader in making an easy determination of the refractivity, N, 

 value from pressure, temperature, and relative humidity data. Standard 

 pressure values of 700, 850, and 1000 mbar have been used for the tables. 

 The tables are at every 10 percent relative humidity and for every degree 

 centigrade ranging for —45 to +45 °C. 



Interpolation for the A^ tables is accomplished in the following manner. 

 First, round the temperature to the nearest degree, then interpolate 

 linearly for the values of pressure, P, and relative humidity, RH, used. 

 No distortion is introduced by this method as the wet term, W (as de- 

 scribed in chapter 4), is a linear function of RH, and the dry term, D, is 

 a linear function of P. 



Example: 



and knowing 



then 



Given P = 980 mbar 

 RH = 47 percent 

 T = 22 °C 



D = D(P, T) 



N = N(P, T, RH) 

 W = W{T, RH), 



Z)(850, 22) = A^(850, 22, 0) = 223.6 A^ units. 

 Z)(980, 22) = A^(980, 22, 0) = 223.6 (980/850) 



257.8 N units. 



