The Denge Sound Mirrors
These three concrete structures were built shortly after World War One, and formed part of a network of such mirrors intended to track aircraft across the country. The spherical surfaces reflect sound waves in much the same way as radio signals from satellities however by using spherical rather than parabolic dishes some measure of the direction can be obtained without having to physically move the dish .....
However before the network could be completed they fell into disuse as the speed of aircraft increased, the accuracy and range fell short of what was required.
For a detailed description of the structures visit the website Denge sound mirrors. Access to the site is very restricted with only a few days each year when access is available see the Romney Marsh Countryside Project for details.