PSN-L Email List Message
Subject: Re: Which is which?
From: Brett Nordgren brett3nt@.............
Date: Sat, 12 Sep 2009 13:58:23 -0400
Hi Bob and Karl,
I'm not sure I got what you were looking for, but gave it a try. See:
http://bnordgren.org/seismo/TvsFBV02.jpg This is a screen capture of two
instruments recorded during a quiet time this morning. The upper trace is
the FBV and the lower one is the Trillium. We have been looking at data
like this for quite a few months, with the goal of getting the noise at all
frequencies of interest, reduced to the absolute minimum possible.
The p-p signal for the larger 'wiggles' is about 10-15 counts which x the
sensitivity for this particular FBV of about 14.4 nm/s/count gives roughly
200 nm/s p-p of seismic noise. Most of the noise appears to be from
microseism energy below the 12.5 sec 6-pole low-pass filter cutoff
frequency. It is clear from comparing the two traces that in the frequency
range used here, 50 sec. to 12.5 sec., the instrument noise is somewhat
smaller than the seismic background, probably only a few counts p-p. Note
that the gain of the Trillium here is about 17% higher than the
FBV. WinSDR doesn't let me fine tune it to the same degree that I can in
The initial transient is WinSDR's filter response to a DC offset, which in
this case was larger for the FBV. Usually the Trillium has the greater
offset as it seems to have a significantly larger response to temperature
At this point I am certain that the FBV instrument noise will be smaller
than the seismic background in all but the quietest amateur locations. Of
course there is always the ANMO borehole in New Mexico. That's pretty quiet!
Let me know what else might be of interest.
At 11:37 AM 9/12/2009 +0000, you wrote:
>The seismograms look like they came from the same sensor to me. But...if
>they didn't, I'll be building one of your FBV instruments!
>Could you show us another two seismograms with background noise and then
>physically/electrically offset the FBV to identify it?
Watch our wiggles
or watch some very very good wiggles
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