Coastal multipath fading

While flight testing airborne satellite communication systems, two-ray multipath fading has been regularly encountered at low satellite elevation angles during over water flights. In addition, an unexpectedly fast multipath fading was experienced as the aircraft transitioned from over land to over water. This unusual multipath fading occurred at medium and high elevation angles where the antenna discrimination should have reduced the reflected signal to an insignificant value. The coastal multipath has been recorded on over twenty occasions by different aircraft using a variety of antennas and flying over various north and central American coastlines. The rate of the multipath fading and fading amplitude suggests that the ocean has a very high reflection coefficient near shore and that some other mechanism such as dielectric wedge diffraction may play a part in the unexplained multipath fading.