Monday, August 8, 2011

Test magnetometer results

Test magnetometer
Magnetometer electronics in their temporary housing.

On Friday I deployed my magnetometer to the same site used by SAMNET for the Lancaster magnetometer. I knew that several coronal mass ejections (CMEs) were due to impact the Earth's magnetosphere. The predictions were correct, on Saturday AuroraWatch UK issued an amber alert. Below is a comparison of the data from my test magnetometer and the SAMNET magnetometer.

Test magnetometer (top-panel) and the D component from SAMNET's Lancaster magnetometer (bottom panel).
Sensor temperature for the same period.
The results are encouraging even though at present the test magnetometer isn't calibrated, and the orientation is only approximately aligned with the magnetic east component ("D"). The baseline differences can be ignored as SAMNET does not make full-field measurements, just variations from a fixed baseline. I haven't measured it yet but the test sensor has a large temperature coefficient; if the FGM-1 behaves in the same way as the FGM-3 then I expect it to be around 25nT/°C. The graph shows the temperature over the same period varied from 16.5°C to 30°C.

Clearly some kind of temperature stabilisation is going to be needed. One option is to bury the sensor. Another is active temperature control, but care will be needed to ensure that DC currents for the heater do not affect the magnetic field being measured!

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