New PEV setpoint, minor geomagntic storms!
Build a Geomagnetic Observatory ! GELLER Labs "Backyard Science"
Thoughts on a proton precession magnetometer design - a Proton Magnetometer Project. Build an Earth's field magnetometer.
The FDM MAGNETOMETER1 project is a low cost high performance proton magnetometer (a digital magnetometer) kit under development for universities and amateur scientists to be able to accurately measure and monitor changes in the Earth's total magnetic F field and to observe geomagnetic storms. Magnetic storms can cause large excursions in the field and are of concern to interests ranging from electrical power grids, radio communications, and satellite operations, to aurora watchers and amateur radio operators.
1 Filter Diagonalization Method "FDM" (harmonic inversion), see Jan 21 and Jan 23 entries, based on: Vladimir A. Mandelshtam, Howard S. Taylor, Harmonic inversion of time signals and its applications, Journal of Chemical Physics (1997), Volume 107, Issue 17, 1997, Pages 6756-6769
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Project Documentation, Links and References (very early stages)
Journal Notes:
Monday, April 18, 2011
Overnight: PDF, TXT, 10:50 am PDF. The geomagnetic field was very quiet until about 3 am local when there was a very fast leading edge waveform which fell off more slowly. Since about 6 am local the geomagnetic field has been unsettled. NRCan OTT PDF. 12:42 pm USGS PDF.
The system performance of the FDM proton precession magnetometer is very good. The overnight figure of merit (FOM) statistical mode was 2e-7 with many values in the e-8 range or even into the e-9 range PDF. There is not enough data yet to get a good Tau 2 to polarization time curve fit, however the curve is begining to fill in (the vertical label should read for a 0.85 V peak envelope voltage) PDF. The polarization time controller shows that the PEV servo is holding up well PDF. I would like to see a bit tighter control of the peak envelope voltage (darker blue curve at ~0.85 V), however with an FOM mode at 2e-7, the system is running well. There was slight disturbance in the Tau 2 record, a now common event suspected to be some kind of limited time span EMI/RFI interference. There was no negative impact on the magnetic record, only the Tau 2 measurement is affected.
Summary of some of the present operational parameters are as follows: NMR fluid 125 mL (4 Oz) Prestone DeIcer, polarization current 1.5 A, polarization time variable (PEV servo 0.85 V setpoint), NBLNA gain 200,000, digitizer scale 1V, resonating capacitor bank 113 nF, nominal local Larmor frequency 2285 Hz. The SWCTRL secondary dump resistor is presently 1.1 k ohms and there is no high frequency snubber capacitor (this topic needs to be revisited).
Tuesday, April 19, 2011
Overnight: PDF, TXT Overnight there were some small relatively slow disturbances (~5 nT or less), then this morning there was a noticeable (although slight) inclrease in geomagnetic activity at sunrise.
The FDM proton precession magnetometer system performance continues at the recently improved level with a consistant statistical mode figure of merit (FOM) value of 2e-7, the lowest long term FOM mode value to date. FOM values continue to populate the 1e-8 range and dip into the 1e-9 range. PDF. The polarization controller has been running well in the PEV servo mode. PDF, might try to run in the Tau 2 feed forward (FF) mode for a while now that we have more Tau 2 - polarization time data for the present operating configuration PDF. (We need more data over a wider temperature range to see if a polynomial (perhaps a quadratic fit) or exponential fit is better).
Also, with the present peak envelope voltage set point of 0.85 V and a +/- 1 V scale on the USB 6008 digitizer, we are preserving more envelope detail, even with the expontial windowing (apodization to emphasize the early portion of the precession waveform) which might be contributing to the improved FOM values, example (see waveform upper left) PDF.
Early evening: There was an odd and very steep positive shift in the geomagnetic field this evening (the positive "pulse" before that is from our 18 nT offset vehicle temporarily out and then returned) PDF. My first reaction was to check the garage to see if the car was still there! The shift was seen at many of the geomagnetic observatories in North America, USGS PDF, NRCan OTT PDF. Late Evening: Geomagnetic conditions are unsettled PDF, NRCan Space Weather PDF.
Wednesday, April 20, 2011 - Geomagnetic Field Active, K4, Kp 5
Overnight: PDF, TXT. There was a relatively large slow storm like negative excursion in the active geomagnetic field overnight. There were K4 conditions with a global Kp 5 index. 9:56 am PDF. 7:45 pm PDF, the field has returned to quiet. System performance continues to be exceptional with the statististical mode holding at 2e-7, the best figure of merit (FOM) mode seen to date. PDF. Wind speeds are back up gusting to 30 mph at the sensor stand, with no apparent adverse affects. Probably the high scatter seen last week was a combination of an unsettled geomagnetic field combined with the NBLNA gain having been inadvertantly set too high. The % success rate has settled in at 77%, a now well known value for a FOM auto-retry threshold of 2e-6.
All seems well again. Time allowing, probably the next jobs are to revisit the SWCTRL snubber capacitor question and to continue to explore the relationship between Tau 2 measured values and polarization time for a given NBLNA gain.
There is an interesting opinion article at the AGU Space Weather site regarding what the next solar cycle might look like. The author points out that even if there is relatively low solar activity on average, there still could be superstorm, as happend, for example, in 1859 during the Dalton minium.
Thursday, April 21, 2011
Friday, April 22, 2011
Overnight: PDF, TXT. It is interesting to watch the Tau 2 - Polarization time graph continue to fill in PDF. Performance continues to be high with a figure of merit (FOM) statistical mode (most common value) holding at 2e-7 PDF.
Saturday, April 23, 2011
Monday, April 25, 2011
Tuesday, April 26, 2011
Overnight: PDF, TXT. There was an unsettled period just after sunrise; we have seen this several times in April. A strong thunderstorm last night did not cause any changes at all in the magnetogram (showing a good immunity to lightning EMI/RFI).
Wednesday, April 27, 2011
Overnight: PDF, TXT. The geomagnetic field was flat overnight (for a few hours, fixed value, outdoor calibration quality). The field become slightly unsettled at sunrise, a not uncommon phenomena this month.
Thursday, April 28, 2011
Overnight: PDF, TXT. The system is running flawlesly with a figure of merit statistical mode of 2e-7. There were severe thunderstorms overnight with no perceptible changes in the field plot. The polarization controller curves (post processing in Excel) show that the peak envelope voltage (PEV) servo is holding the desired peak envelope voltage of about 0.85 V (darker blue) curve well within reaonable limits PDF. The PEV servo works by automatically adjusting (servo-ing) the polarization time (dark red curve) to achieve the desired precession waveform filtered envelope peak voltage (darker blue curve). The PEV calcuations are based on an expontial curve fit of the raw precession waveform filtered envelope, which is taken each measurement from the raw digitized precession waveform data.
Friday, April 29, 2011 - G1!
Overnight: PDF, TXT. There was 10 nT slow waveform in the magnetogram overnight, otherwise the geomagnetic field was quiet here in upstate, NY (US). Afternoon: There was 20 nT rapid positive change in the field geomagnetic this afternoon PDF. The geomagnetic field is active (still sub-storm) 6:00 pm PDF. Now a G1 minor storm! 7:41 pm PDF. The field is still quite active. With the last negative swing, the total change in the F scalar today is approaching 100 nT. A couple of the one or two point step chnages were caused by parked vehicles in our detection range (various widely by vehicle type with size and ferrous content). 10:03PDF.
Saturday, April 30, 2011 - Another stormy day - G1 (minor) magnetic storm!
Overnight: PDF, TXT, full storm view (with a couple of relatively large arrived/departed vehicle steps) PDF, mid morning, still unsettled PDF. Early evening: the field has worked its way up about 50 to 60 nT all afternoon in a minor storm like pattern PDF. Late evening: PDF.
The figure of merit (FOM) values continue to run commonly into the e-8 range with a number of values in the e-9 range. The statistical mode (most common value) contines at 2e-7 PDF. The success rate is running at 82% to 83% for a FOM threshold of 2e-6. On the 2.5 V USB 6008 ADC scale with an NBLNA peak envelope voltage of 2 V, it had been running 77% to 78%. This might be related to slightly less distortion visible on the precession waveform with exponential apodization display now that we are using a 0.85 V NBLNA peak voltage (less NBLNA gain) and the 1 V USB 6008 scale.
Project Documentation, Links and References (very early stages)
QUESTIONS/COMMENTS/notice of typos, etc. send email to joegeller @ gellerlabs dot com
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