A computer-implemented method includes: receipt and accession of magnetic field data from a constellation of satellites providing global coverage over the Earth in a time span less than one day; inter-calibrating the magnetic field data from all satellites to a common standard; quantifying the global magnetic disturbance and selecting quiescent intervals at least as short as one day for evaluation of Earth's internally-generated field; calculating global maps of the mean vector magnetic field for each quiet interval from the average of all satellite measurements in angular bins; converting the time sequence of global maps of the mean fields to time series of angular harmonic coefficients via direct convolution; applying spectral and regression analysis to the harmonic coefficient time series to identify and remove artifacts in the signals; reconstructing a continuous time and spatial representation of the magnetic field continuous in time and angular position globally.