INTRODUCTION 



233 



Figure 6.5. Correlation coefficients of seasonal cycles o/ Ng and Lb: night 

 {2000, 2200, 2400) versus the standard deviation of Lb- 



the sensitivity of £" to a unit change in f{n). The intercept, a, is a func- 

 tion of path length, antenna heights, and terrain characteristics, and can 

 be derived from existing prediction procedures [9]. Comments on some 

 results obtained are given in the remainder of this section. 



6.1.2. Parameters Derived From the N-Profile 



It has long been recognized that the variations in field strength on 

 transhorizon paths are intimately connected with changes in the vertical 

 gradient of refractive index over the path. Although our knowledge of 

 the detailed fluctuations in refractive index in the troposphere is still in- 

 adequate for many requirements, it is nevertheless possible to relate, 



