252 



TRANSHORIZON PARAMETERS 



6.2.6. Elevated Layers at Temperature Inversions 



Recent radar and refractometer investigations of tropospheric structure 

 have shown that elevated layers in the refractive index distribution are 

 frequently observed in the stable air of temperature inversions [38]. 



A typical value of layer thickness is 100 m, with horizontal dimensions 

 of tens of kilometers. On occasions, extended layers no more than 10 m 

 in thickness have been detected by refractometer soundings. In the 

 present discussion we attempt to evaluate the reflection coefficient of 

 these elevated layers. We may express the modulus of the reflection 

 coefficient \p\, for a wave incident at a glancing angle a on a layer of 

 thickness h, and horizontal extent, x, in the form: 



An 



f(a, h, x) 



(6.4) 



where f{a,h,x) is the ratio of the reflection coefficient of the model to 

 that of the infinitely sharp case (i.e., the Fresnel discontinuity value, 

 An/2a2). This function has been evaluated for several layer profiles [28], 



24 

 o 



u. 



H 

 o 



5 12 



-16 -12 -8 -4 4 8 12 16 "0 4 8 12 16 20 24 28 32 36 40 



OBSERVED FIELD OBSERVED FIELD 



28 r 

 24 



_i 



LlJ 



il 16- 



Q 

 UJ 



h 12- 



-12 -8 -4 4 8 12 16 20 24 16 -12 -8 -4 4 8 12 16 20 24 



OBSERVED FIELD OBSERVED FIELD 



Figure 6.14. Com-parison of observed radio field strengths and values predicted for 



wintertime afternoon hours. 



