...
dpar(start="2011 jan 4 4:30",lenmin=30)
iod = prep("kh2oV#7")
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SUMMARY:
1. It appears that this problem was due to RF environmental factors unique to CWEX11. It is not physical since we do not see noise on the Li7500 H2O signal or any other scalar.
2. We have no way of detecting whether noise occurred on the lower-rate analog channels.
3. Since we can fix the CWEX11 data in software (FFT; filter spectra; inverse FFT), we do not need to know the source.
4. We are not sure that we will ever use the same serializers (or kryptons) again, but we should look for this noise again in any case.
5. IF we wanted to pursue this further, we could take the station to the turbine test station at NREL, though there still may not be exactly the same RF environment.
6. We should keep track of the frequency and amplitude of the noise while correcting the CWEX11 data. We also may get turbine operating parameter data (rotation speed?) from the wind farm operator. This log entry may be revisited with a check of whether these values are correlated.
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Postlude:
Contrary to summary comment 2 above, I now note that noise is apparent in the PTB220's pressure signal as well. This occurs all the time at stn2 and some of the time at stns 3&4. Note that it is impossible to detect that it is 2Hz noise, since the sampling rate is 1sps. Also note that this stn 2/4 behavior is opposite that seen in kh2oV, where the noise was continuous and large at stn 4 and much less and variable at stn 2. The bottom-line conclusion probably doesn't change -- the source likely is RF and the effect on a sensor depends on some nuance of mounting and cabling.
Unfortunately, this "noise" appears to preclude the use of pressure to identify the existence of turbine wakes at the surface, though it might be possible to pull out a signal...
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Addendum:
During CentNet tests at Marshal during the first half of 2012, the 2 Hz noise gradually appeared (as the krypton signal response declined?), to the point that it is quite obvious in the June-August data. Thus, I don't think we can blame the turbines after all...