Sunday, January 13, 2013

Magnetometer progress report

About AuroraWatchNet

I am developing a simple, low-cost, battery-powered magnetometer for auroral alerts and citizen science. It is intended to be wireless to allow easy installation, a unique feature as far as I am aware. The magnetometer uses my own Calunium micro-controller board, which is an Arduino clone based on the ATmega1284P micrcontroller. Data is sent via a radio link to a Raspberry Pi base station which will then forward the data to AuroraWatch UK. I am hoping to deploy a network of such magnetometers in 2013 to enable AuroraWatch UK users to contribute data to improve the service. If you want to track the development then follow @aurorawatchnet on Twitter. 

The first AuroraWatchNet magnetometer is currently running in my garden. The environment is not ideal as I can see disturbances from cars and even the garage door being opened but it is convenient for testing and representative of what to expect from user-contributed data. I have been comparing the results from our SAMNET magnetometers with the AuroraWatchNet prototypes and generally the results are very encouraging given the difference in cost between the two systems. Now I can plot the AuroraWatchNet magnetometer data in the standard AuroraWatch UK style, using the same Octave code. Below is a comparison of today's plots. 

AuroraWatch UK

The data is taken from SAMNET's Lancaster magnetometer. The X axis is time and the Y axis shows the magnetic field strength in the direction of magnetic North (H component) in nanotesla (nT) relative to an unrecorded baseline. This exact plot appeared on AuroraWatch UK. We would normally expect cleaner data but our Lancaster site has recently been experiencing some interference.

SAMNET data from Lancaster, as used by AuroraWatch UK

AuroraWatchNet test magnetometers

The plots below correspond to the same time interval as the plot above. The first plot is from my garden magnetometer.

AuroraWatchNet data from near Lancaster.

The Y axis again records magnetic field strength but this time it is the absolute field. This magnetometer is operating in power-saving mode, turning off the sensor when not needed. This slightly increases the noise level but I hope will give one year of operation from two D cells.

Another AuroraWatchNet magnetometer has been deployed almost adjacent to the SAMNET magnetometer we already use for AuroraWatch. In this system the magnetometer sensor is continually powered, resulting in reduced noise levels. The alignment with magnetic North is only approximate. 


AuroraWatchNet data from the Lancaster University field station.

Conclusion

The AuroraWatchNet magnetometers are sufficiently sensitive and stable to make useful contributions for auroral detection and citizen science. My experience with the garden magnetometer suggests that in many cases performance will be limited by the noise at the site, rather than the magnetometer.

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