Geomagnetic navigation beyond the magnetic compass

Increasing uncertainty regarding the reliability of Global Navigation Satellite Systems (GNSS) has led the navigation community to seek valuable alternatives. Aerospace navigation by integration of inertial systems with reference to maps of Geophysical Fields of the Earth (GFE) is a promising area which can be highly advanced utilizing tremendous achievements in embedded micro-processing, including the memory devices capability and miniature size. GFEs are the properties of the planet Earth. Most GFEs are already well mapped in geographical system coordinates. GFEs can't be destroyed or changed in the foreseeable future. They don't require special service, therefore, they can be considered as a solid source of navigation information. EMF maps, models and charts, which are currently used in a wide range of commercial and military applications, mostly for directional information, are periodically updated and can be used as a reliable navigation reference on at least 98% of the Earth's surface including water covered areas. This paper presents a brief review of terrain navigation efforts (using land topography and geomagnetic maps) in the last 50 years. Information about the accuracy of existing EMF maps is discussed. The geomagnetic methods position and velocity determination, along with potential accuracy and major sources of error, are reviewed. EMF parameters dependency on altitude and mapping for different altitudes, including the effect of daily variation are addressed and discussed. The paper includes a description of an integrated navigation system utilizing the correlation principle of actual coordinate determination by finding the best fit between the geomagnetic profile measured onboard during the flight and the corresponding profile in a stored on board map. The precision fluxgate magnetometer can be employed for high accuracy measurement of EMF vector components and the anomaly part of EMF on board of aircraft is described. This paper also addresses the problems of precision measurement of EMF on the aircraft and gives recommendations to secure such measurements in the aircraft environment.