Some observations of distance dependence in tropospheric propagation beyond radio horizon

This paper shows analytically that the distance exponent, n, obtained by comparing power levels at two points beyond radio horizon depends upon (i) the region beyond horizon where these points are located (diffraction or forward scatter region), (ii) the relative positions of these points, (iii) the initial gradient of refractivity and (iv) heights of the antenna terminals. In the diffraction region, the exponent critically depends upon (ii), (iii) and (iv) above. In the forward scatter region, the absolute value of n critically depends upon (iii) and (iv) but not on (ii). Observed results on variation of n over three paths (200 to 700 km) to illustrate these points have been presented. It has been shown that for paths with complicated geometry, angular distance exponent depends much less on path geometry and initial gradient. From the transmission loss data, possible values for spectral slope, m, in the relation ¿(K) ¿ K¿m and scattering parameter Cn2 have been indicated.