GPS-Free Operation of Ships and Aircraft Utilizing Terrestrial Satellites

Modern aerial and naval navigation systems utilize the GPS technology extensively to retrieve the own position information automatically, which in turn is fed into other navigation and warfare systems through a serial link. A failure of the GPS system would result in a significant loss in speed and accuracy of any navigational calculation, making it nearly impossible to maintain a reliable and automated operation in air or at sea. This paper investigates the feasibility of utilizing the long range radar transmissions incident on vehicle's electronic support system measures (ESM) that is composed of direction finders. By simple triangulation of the Radars uncertain directions and adaptive filtering, an alternative automated local positioning system (LPS)would be very useful in case of a GPS-free operation. In this paper, we evaluate the operation of the proposed LPS technique by simulation. A certain number of terrestrial Radars were randomly located on land and a ship is simulated to navigate on the open seas. The islands and land structures that would prevent the Radar beams to reach the ship were taken into account and the blockage of such rays were calculated using image processing of the Navigation maps pixel values. The triangulation and positioning errors were calculated and the noise was cancelled by adaptive filtering using linear Kalman filter. With the simulation experiments, we show that such an LPS system is feasible and could be integrated to the ships ESM systems to provide an automated and reliable own ship position information in case of a GPS failure.