Geomagnetic field gradient measurements and noise reduction techniques in Colorado

Abstract

Two rubidium narrow line magnetometers were operated in a differe, ntial mode along a 12-km base line near Boulder, Colorado, and the total field gradient measured to high accuracy. A number of runs of difference field were made from March through September of 1974. The results showed that daily averages were generally constant to within +0.1 • during quiet or disturbed periods with the exception of a few days in late August and early September. The agreement is eXCellent between the observed difference field and a difference field calculated from the measured east-west field Y and a transfer function appropriate to a local conductivity anomaly. Accounting for the effect of the anomaly typically permits a reduction of a factor of 3 in the standard deviation of the daily average; on very disturbed days a reduction of a factor of 5 in gradiometer noise was achieved. For periods of more than several days the corrections for anomaly edge effects are comparatively small.

Study on noise in simultaneous geomagnetic difference data caused by the effect of S q local-time variation

“…For example, the terrestrial noise resulted from the non-uniform medium of crust is just one kind. So, a lot of research on the secondary noises, especially on the terrestrial noises, has been reported in recent years (Beahn, 1976;Davis et al, 1981;Poehls and Jackson, 1978;REN et al, 1993REN et al, , 1998.…”

Tectonomagnetic event detection using empirical transfer functions

“…Smith and Johnston [1976] have utilized station differences with time averaging to reduce daily variations and their associated induction effects. Brill [1975] and Beahn [1976] carried this technique one step further by introducing a differential form of the transform function method where data from a reference vector magnetometer are used to help eliminate induced magnetic field effects from the differenced total fields. In this paper we construct a transfer function between a reference vector magnetometer and a total field magnetometer at an observation site near the San Andreas fault in central California.…”

Study on eliminating noises in short-period data of geomagnetic intensity by using numerical multichannel predictive filtering

“…There has been some reports about the applications of this technique to daily averages and values recorded at 21:00 everyday of total field (Beahn, 1976;Poehls and Jackson, 1978;Davis, et al, 1981;Davis and Johnston, 1983;Ren et al, 1993). However, it is indubitable that there exists a close physical relationship between the secondary and original fields.…”