Magnetic Data Reduction of Basement Correction
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Date
2013
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Publisher
Uva Wellassa University of Sri Lanka
Abstract
The magnetometer survey is a passive geophysical technique that measures the contrasts of
magnetic properties between the feature of interest and its surrounding environment. This
technique has wide applications in mineral and archeological investigations. Rocks and minerals
with high ferrous content provide anomalous signatures than the background enabling to screen
them.
The magnetometer surveys are always disturbed by temporal variations: Diurnal variation,
Magnetic storms and Micro-pulsation, which depend upon the time and space. Magnetic
surveys are not done during magnetic storms. The diurnal variation cannot be avoided and the
noise will disturb the data quality. To eliminate the diurnal variation from data a base station is
used in magnetic surveys.
In order to overcome the temporal variations, a base magnetometer is needed to correct these
time dependent variations. . While the base records the temporal variation of the area the rowing
magnetometer records both the temporal variation and the local anomaly. For a large-area
survey, or an airborne survey, the magnetic field may be monitored at several locations,
continuously, to identify the spatial variations of the time-varying field.
If the rover is too far away from the base station, the time-varying fields measured at the rover
will differ from those measured at the base station, resulting in increased error. The effective
range of a single base station is generally considered to be less than 100 km for air-borne survey
and for a ground survey it is about 200 m. This distance may vary according to the survey area
and the expected accuracy.
Owing to the large area covered by an aeromagnetic survey, a single magnetic base station
would not have provided adequate coverage. Instead, several base station magnetometers are in
operation during the survey (Hrouda et al, 2009).
The base correction is conducted with the assumption that the environmental effects over the
survey area are constant. The base magnetometer is synchronized with the rowing component
and the environmental effect is removed according to the respective time stamps. However, if
the survey area is large, the base station needs to be shifted as the assumption is no longer valid.
As the crustal magnetic component of locations where the base station(s) establish during a
survey is not a constant, a correction is needed to be applied for base stations. The present work
attempts formulating a model for the basement correction.
Methodology
A mathematical model that completely describes the magnetic surveys, with two sub surveys
was created. This method can be extended for many sub surveys, considering two sub surveys at
a time. The variables were: IGRF value, local anomaly, environmental noise, local anomaly at
the base station, and the location.
Description
Keywords
Mineral Sciences, Mineral, Geographic Information System, Geophysical