Effect of super-refractive layers on tropospheric signal characteristics in the Pacific coast region

Results of tropospheric radio wave propagation measurements over two paths between San Nicolas Island and the California coast near Pt. Mugu are correlated with the characteristics of refractive index profiles determined at the path terminals simultaneously with the radio measurements. The radio paths extend to the vicinity of and slightly beyond the radio horizon. Specifically, it was found that the existence of super-refractive layers (either ground-based or elevated) favors the occurrence of prolonged space-wave fadeouts for the within-the-horizon path, and increases the short-term fading range for the beyond-the-horizon path. It was found that the base and top elevations of a super-refractive layer, and also the magnitude of the refractive index gradient within the layer have a noticeable effect on various characteristics of the received signal for both paths. An example of this is found if the hourly median basic transmission loss for the beyond-the-horizon path is plotted as a function of the layer heights. These results generally agree with earlier observations by Smyth and Trolese.