Chapter 6. Transhorizon Radio- 

 Meteorological Parameters 



6.1. Existing Radio-Meteorological Parameters 



6.1.1. Introduction 



A method of predicting the statistical distribution of field strength on 

 transhorizon paths is an important requirement m tropospheric wave 

 propagation. Consequently, considerable attention has been given in 

 recent years (see figs. 6.1 to 6.6) to studies of the correlation between the 

 measured signal level (e.g., the monthly median value) and some quantity 

 derived from surface or upper air meteorological data. Figures 6.1 to 6.6 

 show relationships between field strength and various meteorological 

 parameters. It can be seen that there are some quite marked similarities 

 (high correlation coefficients) between the two. It thus appears that if a 

 reliable "radio-meteorological parameter" could be developed, then 

 generally available meteorological data would replace expensive radio 

 measurements in deriving the required distribution. 



Progress has already been made in this difficult problem, [1, 2]^ In 

 these investigations, special attention has been given to two parameters: 

 (a) the surface value of refractivity, N s, and (b) the difference, AN, 

 between A''^ and N at a height of 1 km, Ni. Other groups have studied 

 different parameters [3, 4, 5, 6, 7, 8], either as possible alternatives to 

 N s and AN in the prediction process or as quantities which clarify the 

 effect of meteorological features, such as anticyclonic subsidence, on 

 signal strength. It is evident from the literature that some difference of 

 emphasis exists regarding the relative merits of the parameters proposed 

 to date, and particularly on the value of studies of N s- 



This chapter provides a critical survey of the present position in this 

 field of radio meteorology, and indicates a new approach which incor- 

 porates some aspects of all existing treatments. Section 6.1 contains a 

 study of previous work and attempts to put the various views in proper 

 perspective; section 6.2 discusses some selected radio data from VHF 

 paths and its classification in terms of refractive index profiles, while 

 section 6.3 introduces a parameter combining the concepts of refraction 

 and atmospheric stability, and compares its properties with those of 

 existing parameters. 



1 Figures in V)rackets indicate the literature references on p. 2()t). 



22!) 



