Internal reflection in the troposphere and propagation beyond the horizon

Since the last year of World War II, the outstanding problem in tropospheric propagation research has been the explanation of the high observed field, strengths well beyond the horizons of high-power transmitters, at all frequencies throughout the vhf and microwave spectrum, in widely separated parts of the world under vastly different conditions of climate and terrain' The disagreement between measurements and calculations based on conventional theory of propagation over a smooth earth surmounted by an atmosphere with standard refraction (4/3 earth) has become steadily worse as the powers and distances have increased, so that the term "discrepancy" seems like a considerable understatement, 40 db and more discrepancies of median observed fields above the conventionally calculated value being not at all uncommon beyond 100 miles. Discussion and references appear in recent annual progress reviews on tropospheric propagation. 1, 2, 3