| Quote from elog 2237, 11 Nov 2009: |
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The attached plot shows the spectra of the 3 Z axes of the 3 seismometers we have (this data is from ~20Aug2009, when the Ranger was in the Z orientation) in Magenta, Cyan and Green, and the noise of each of the sensors in Red, Blue and Black. The noise curves were extracted from the spectra using the Huddle Test / 3 Corner Hat method. The Blue and Black traces which are just a few points are estimates of the noise from other spectra. The Blue points come from the Guralp Spec Sheet, and the Black comes from the noise test that Rana and I did the other day with the Ranger (elog 2223).
I'm not really happy with the black spectra - it looks way too high. I'm still investigating to see if this is a problem with my calibration/method....
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So, as it turns out (surprise), I'm a spaz and forgot a 2*pi when calibrating the Guralp noise spectra from the spec sheet. I noticed this when redoing the Huddle Test, and comparing my Spec Sheet Guralp noise with Rana's, which he shows in elog 2689. When going from m/s^2, the units in the spec sheet, I just tilted the line by a factor of frequency. Koji pointed out that I needed a factor of 2*pi*f. That moves the Guralp spec line in the plot in elog 2237 (to which this entry is a reply) down by ~6, so that my measured noise is not, in fact, below the spec. This makes things much more right with the world.
In other news, I redid the Huddle analysis of the 2 Guralp seismometers, ala Rana's elog 2689. The difference is now we are on the granite slab, with soft rubber feet between the floor and the granite. We have not yet cut holes in the linoleum (which we'll do so that we're sitting directly on the 40m's slab).
Rana> this seems horrible. Its like there's a monster in there at 6-7 Hz! Either the seismos are not centered or the rubber balls are bad or Steve is dancing on the granite slab again.
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