Magnetic Maps and Models for Alternative Navigation

Magnetic navigation requires the comparison of onboard magnetic sensor measurements to reference magnetic maps and models. Magnetic maps and models are available at a wide range of scales and scope. At any given location, measurements of the ambient magnetic field are the sum of various components, including sources internal and external to the Earth. This paper discusses maps and models of the internal components sourced in the core and lithosphere of the Earth. The long-wavelength, slowly-time-varying core field of the Earth is represented by global, satellite-based models. The time-invariant lithospheric magnetic field is represented at its longest wavelengths by spherical harmonic models based on data from the CHAMP and SWARM satellite missions and at resolutions smaller than ~300 km by grid products based on the processing of airborne, marine, and ground surveys. Regional to local magnetic anomaly maps and grids are available for selected areas at resolutions down to 100 m. Evaluation of possible map/model performance for a given magnetic navigation scenario requires consideration of amplitude and frequency of magnetic field variations, and magnetic map/model uncertainty. We present a basic analysis of magnetic navigation signals as a function of altitude and velocity.