Effects of the Earth's curvature on radar tracking systems

Traditionally airborne radar tracking systems have employed a variety of spatial reference frames which are either inertial (north-east-down) or body-axes (forward-starboard-down). These frames are exclusively Euclidean 3-space in nature and, with the sole exception of Earth-centred coordinate frames, take no account of the spherical properties of the Earth over which they are operating. The increasing demands for accuracy being placed on airborne radar tracking systems make it clear that the effects of Earth curvature must be properly addressed. The cumulative angular error between an inertial NED frame which has only been translated in 3 space and a true rotating spherical frame (in latitude, longitude and altitude coordinates) is examined. The cumulative angular error resulting from the use of a Euclidean 3 space, as opposed to a spherical, coordinate frame is shown to compromise seriously the achievable accuracies for an airborne radar tracking system. A solution to this problem is presented along with complementary solutions for the test environment.