1. C. Turbitt, O. Baillie, D. Kerridge, E. Clarke
An Investigation Into Techniques For Isolating Noise In Observatory Data
C. Turbitt, O. Baillie, D. Kerridge, E. Clarke

2. Observatory noise sources
Man-made:
Localised interference (vehicles, power lines, RF, etc.)
Instrumental noise
Processing (scaling, baseline fitting, etc.)
Natural
Localised current systems (induction effects, etc.)

3. Detecting noise – instrument comparisons
Where one or more instruments operate at an observatory, inter-comparisons readily indicate instrument noise, processing errors & localised disturbance.
Not, capable of detecting noise from a distant source or detecting systematic processing errors.

4. Detecting noise – observatory comparisons
Nearby observatories can be compared with tools such as the INTERMAGNET CD Viewer
Relies on nearby, good quality observatory.

5. First difference RMS Plots
Love, J., 2006

6. First difference RMS Plots
Transfer function of a first difference filter shows the limitations of using first differences to measure signal amplitude.
A first difference is a high pass filter with slow roll-off:
3dB/octave at 10 minutes
-3db point at 6 minutes
Is there a technique that can better isolate noise from the natural signal?

9. Step 1: Window in the time domain & FFT

10. Step 2: Window in the frequency domain

11. Step 3: Sum power & plot LSD v geomagnetic latitude

12. Artificial noise: 5nT at 6 minute period

13. Artificial noise: 5nT at 120 minute period

14. Artificial noise: 0.5nT at 3 minute period

15. Artificial noise: 0.5nT at 3 minute period

20. Conclusions R Project http://cran.r-project.org/
Observatories are encouraged to look at noise by comparing signal amplitudes against other observatories of similar latitude
RMS of the first differences is a useful method to detect noise above the natural signal in the band around 6 minutes period for a one-minute data
Linear spectral density plots can be used to detect noise at lower frequencies and also, by limiting the band, detect low amplitude noise at high frequencies
Limitations:
Unable to detect transients (steps, spikes) or timing errors
Periodic noise signal of amplitude > natural signal
-60 ° < Geomag Latitude < +60°
R Project