The Impact of Evaporative Ducting on Covert Communications

This paper provides a brief primer on tropospheric ducting and examines the potential impact that evaporative ducting has on the intercept vulnerability of covert communication systems. The study considers the intercept vulnerability of a generic ship-based satellite terminal in the presence of evaporative ducting when the threat consists of a total power radiometer. The terminal uplink power is computed to achieve a specified bit error rate at the satellite receiver, which is assumed to be at a geosynchronous altitude. The intercept receiver is assumed to operate by processing intercepted energy from the side lobes of the satellite terminal uplink signal. Both near-surface and airborne threat platforms are considered and a vulnerability analysis is performed for different RF frequencies and uplink data rates. The results demonstrate that evaporative ducting is capable of significantly increasing the intercept range of the satellite terminal when the threat is located near the Earth´s surface. By comparison, however, the impact of evaporative ducting is shown to be comparatively minor when the threat receiver is on an airborne platform. This paper addresses an important aspect of ducting that is underrepresented in the literature - the linkage between ducting and communication covertness.