Cobra Mist was the codename for an Anglo-American experimental over-the-horizon radar station at Orford Ness, England. It was known technically as AN/FPS-95 and sometimes referred to as System 441a; a reference to the project as a whole.
The former Cobra Mist building in October 2004
Radiating lines at the site
Over-the-horizon radar (OTH), sometimes called beyond the horizon radar (BTH), is a type of radar system with the ability to detect targets at very long ranges, typically hundreds to thousands of kilometres, beyond the radar horizon, which is the distance limit for ordinary radar. Several OTH radar systems were deployed starting in the 1950s and 1960s as part of early-warning radar systems, but airborne early warning systems have generally replaced these. OTH radars have recently been making a comeback, as the need for accurate long-range tracking has become less important since the ending of the Cold War, and less-expensive ground-based radars are once again being considered for roles such as maritime reconnaissance and drug enforcement.
How a skywave OTH radar works: A powerful shortwave signal from a large transmitting antenna (left) reaches a target beyond the horizon by refracting off the ionosphere, and the echo signal from the target (right) returns to the receiving antenna by the same route. In practice, the beams are much closer to the horizon than shown here.
Duga radar array, near Chernobyl
Coverage of the three U.S. Navy ROTHR stations in Texas, Virginia, and Puerto Rico
Transmitter array, Sector 6, Christmas Valley, Oregon
