Noise Reduction Techniques for Use in Determining Local Geomagnetic Field Changes

Measurements of the difference in total field $\Delta$F(t) have been made over a 16 km N-S path near Boulder. The behavior observed is quite different from that for an E-W path. The present accuracy of the narrow line rubidium magnetometers used is about 0.01 $\gamma$. The N-S variations appear to correlate mainly with variations in H rather than D, and may be associated with either gradients of external fields or currents in shallow conductivity anomalies. More recently three magnetometers have been set up on a straight E-W line so that the second difference can be measured, and a transfer function from field component variation to the second difference can be determined. A generalization of this approach will be used for analyzing USGS tectonomagnetic data from California.