262 TRANSHORIZON PARAMETERS 



where, for convenience, 



n 77 A ^' H w 77.6 (4810) e., 

 D( = 77.6 — and Wt = y~2 



Applying the same approximations as in the derivation of (6.18), one 

 obtains 



In iV^ = In A^, - r^z (6.24) 



where 



!„* fe+0«*^' 



2c 



For the standard conditions assumed above and eo corresponding to 

 60 percent relative humidity, H^ '^ 7.5 km. Again, the form of the wet 

 adiabatic lapse of A^ is given by 



A^^ = A^, exp i-T^z), z> i. (6.26) 



We shall now apply these results to the derivation of a refractive index 

 turbulence parameter. 



6.3.4. The Turbulence Parameter, n 



Analogously to the concept of thermal stability, we define n as the area 

 between the environmental N{z) curve and the appropriate adiabatic 

 decrease of A^. That is 



n = 



/ \N observed ~ N adiabatic j dz (6.27) 



where the integration is arbitrarily taken from the surface to 3 km. This 

 then extends the integration well above the crossover height of the radio 

 horizon rays from transmitter and receiver normally encountered in 

 tropospheric propagation. The integral for n may be written 



n = / Ndz - j No exp (-Tdz) dz 



l>- 



exp[-V^{z-i)]dz. (6.28) 



