A global model of the electromagnetic background noise

We present the recent development of an empirical global model of the electromagnetic background noise. The model takes into account the main contribution from this background field originating from the Earth space environment. The model is developed on the basis of a global geomagnetic field model to find the spatial and temporal variation of the near DC magnetic disturbance across the globe. The extension of this DC level to the full geomagnetic spectrum (up to 10 Hz) is obtained by investigating the statistical behavior of the magnetic spectrum based on experimental data. It is found that the spectrum can be modeled with power laws with exponents linearly dependent on the level of geomagnetic activity, i.e. on the KP index. This linear dependence is in turn a function of latitude and time. The modeled magnetic spectrum as well as knowledge of the electrical conductivity profile in the Earth's crust further permits determination of the electric wave power spectrum with depth. Finally, the model is validated by comparison with experimental electromagnetic data from FOI's test site in the Stockholm archipelago where environmental parameters are known from previous field trials. The model gives excellent results in the higher frequency domain (0.1-10 Hz) while for lower frequencies one must probably account for contributions from ocean circulation. The ability to predict the electromagnetic background noise is important for both civilian, e.g. geophysical and aeromagnetic survey planning, as well as military applications, e.g. to evaluate protection, security and capability of naval systems with the use of tactical decision aids.