80 



TROPOSPHERIC REFRACTION 







50 



300 



350 



100 150 200 250 



Ns[l-exp(ch)] IN N UNITS 



Figure 3.17. Graphic representation of Ns[l — exp(— ch)] in N iinits versus height. 



3.11. A Graphical Method 



Weisbrod and Anderson [16] present a handy graphical method for 

 computing refraction in the troposphere. Rewriting and enlarging (3.11), 

 one obtains 



N,- iV,+i 



T(mrad) = 2^ tttttt: z — n: — o — \ 



k^o 500 (tan dk + tan dk+i) 



(3.49) 



where r will be the total bending through n layers. Terms for the de- 

 nominator can be determined from figure 3.18. Equation 3.49 is essen- 

 tially Schulkin's result with only the approximation, tan dk ~ Ok, for 

 small angles, omitted. 



The procedure for using figure 3.18 follows. Enter on the left margin 

 at the appropriate Ns — N{h). Proceed horizontally to the proper 

 height, h, interpolating between curves if necessary. Use the solid height 

 curves when N s — N{h) is positive and the dashed curves when N s — 

 N{h) is negative. Then proceed vertically to the assumed ^o and read 

 500 tan 6 along the right margin. 



