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12/11/2024 8:42 am
The Earth's magnetic field changes throughout the day due to solar wind and other factors. A base station's data is used to correct for these variations (diurnal variations), which can significantly impact the results of a survey. In general, diurnal variations do not change rapidly, and it is not required to record the Earth's magnetic field at high sample rates. However, during geomagnetic storms, diurnal variations can be so rapid that 10Hz or a higher sample rate is necessary to track the field change. Kp index is commonly used to measure the strength of geomagnetic activity. The diurnal variation on October 11th 2024, when the Kp index reached above 8, was shown in the plot below. Field changes as fast as 5nT/second were recorded. In comparison, the Kp index on October 15th was around 4. The diurnal variation was much slower.
Sometimes if a survey site is close to man-made structures, such as railways, very rapid local magnetic field variations can also occur due to electrical current activities. A high sample rate magnetometer base station is also required in these situations, as well as some expertise in setting up the base station.
