[SAC-HELP] SAC macro for power-spectral-density (noise) plots for seismograph stations

Fiona Darbyshire f.darbyshire at gmail.com
Thu Feb 17 07:50:48 PST 2011


Hello,

Several years ago, I tried making power-spectral-density plots for
noise characteristics of temporary seismograph stations, but it's been
many years since I did this, and I have forgotten the details. One of
my colleagues just sent me a copy of my original macro to ask me about
it, and I find myself second-guessing myself as to whether I did it
right originally. Here's the relevant section of the macro and my
query:

cut 0 1000
r 2011.038.17.00.00.0000.CN.YUK1..HHZ.D.SAC
cut off
transfer from polezero subtype yuk1.pz to none freqlim 0.005 0.006 40 45
dft
divomega
keepam
xlim 0.01 50
div 27.38613
sqr
add 1e-12
log10
mul 10
loglin
p2

When I look more closely at the TRANSFER documentation, I see that if
I transfer to NONE, the result should be a displacement seismogram.
But the divomega in the frequency domain is an integration, so
presumably I was thinking of converting from velocity to displacement
there... does that mean I've effectively integrated twice?
(I also can't remember what the division by 27.3 was for, though my
suspicion is that it was some kind of normalisation...)

If anyone can advise me on this, or anyone has a better SAC macro for
PSD that they're willing to share, please let me know!

Thanks very much,

Fiona Darbyshire
Université du Québec à Montréal




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