Geo-location using direction finding angles

Passive geo-location of ground targets is commonly performed by surveillance air-craft using direction finding angles. These angles define the line of sight from the aircraft to the target and are computed using the response of an antenna array on the aircraft to the target's RF emissions. Direction finding angles are the inputs required by a geo-location algorithm, which is typically an extended Kalman filter or a batch processor. This modality allows a single aircraft to detect, classify, and localize ground-based signal sources. In this article, the direction finding angles used for geo-location are defined and a mathematical model is developed that relates measurements of these angles to the target's position on Earth. Special emphasis is given to the angle measurement provided by a linear antenna array. An algorithm is presented that uses iterated least squares to estimate a target's position from multiple angle measurements. Simulation results are shown for a single aircraft locating a stationary ground target.