Surface Refractivity Research Articles

Investigation of Extended Range VHF Propagation Through Troposphere

The Civil Aviation Department is currently establishing VHF radiotelephone circuits for air/ground communication over long ranges to ensure more effective air traffic control. These systems utilize the phenomenon of VHF propagation beyond the radio horizon. Results of studies on air to ground propagation using one such circuit are presented in this paper.The basic transmission loss derived from these observations is found to be systematically lower than the predicted one based on diffraction and scattering characteristics for a smooth earth model and a standard atmosphere. Studies of surface refractivity Ns, and an upper air parameter ΔN (0·9 km.), defined as the difference between refractivity at the surface and at 0·9 km., give the following results. The parameter ΔN (0·9 km.) at the ground terminal shows good correlation with air to ground signal strength when the value of this parameter is high, but the correlation coefficient is poorer when its value is low. Correlation with Ns is consistently low. Analysis of refractive index characteristics indicates the presence of elevated layers for a substantial part of the period of radio studies. It appears that ΔN (0·9 km.) may be of limited use for long-term predictions and that some other parameter depending upon thermal stability may be more useful for this purpose.

Use of surface refractivity in the empirical prediction of total atmospheric refraction

Use of surface refractivity in the empirical prediction of total atmospheric refraction

Range-error compensation for a troposphere with exponentially varying refractivity

spherically symmetric refractivity which varies exponentially with height. The correction is given as function of surface refractivity and ray elevation angle, and its accuracy and limitations are disc ussed. In the long-range tracking of an object in space by an observer on the earth, systematic errors are introduced by the earth's atmosphere, most of the contribution arising from the troposphere at micro­ wave frequencies. This paper derives an explicit analytic expression for the tropospheric range e1'1'or for a standard atmosphere whose refractivity is exponentially distributed with height. If one measures the delay

Comparative study of the correlation of seasonal and diurnal cycles of transhorizon radio transmission loss and surface refractivity

Comparative study of the correlation of seasonal and diurnal cycles of transhorizon radio transmission loss and surface refractivity

Comparison of observed tropospheric refraction with values computed from the surface refractivity

Radar elevation-angle errors observed in the Tularosa Basin of New Mexico are compared with values predicted from the surface value of the radio refractive index. Although this method of prediction is not particularly efficacious under the conditions of this experiment, encouraging agreement nevertheless was obtained between predicted and observed: a) mean value of elevation angle error, b) variation of elevation angle error with N_{s} , and c), the degree of reduction in the uncertainty of prediction gained over the use of a single-standard atmosphere.

Interdependence Between Hourly Median Transmission Loss and Surface Refractivity Index Observed at 900 Mc on a 232-Mile Far-Beyond-the-Horizon Path

A detailed analysis is made of propagation data obtained from the North Atlantic Scatter System installed in Iceland. In particular, the correlation of the transmission loss and meteorological observations on a long path is analyzed in detail. By separating the data into various time periods, it is shown that for periods of time during which the received field is lowest, the correlation between transmission loss and surface refractivity is very high. The ability to establish a strong correlation between transmission loss and surface refractivity for this period allows the system designer to make more accurate predictions of the lower expected received fields and thus is able to calculate the minimum required transmitter with greater accuracy.