In a message dated 20/01/2007, Bobhelenmcclure@....... writes:

Hi all,
What Dr. Peters wants us to try left me stunned. All that will result is  a 
narrow-band modulated 20 Hz carrier without any useful event  information.
Bob



Hi Bob,
 
    You mean 20 sec period ~ 0.05 Hz?
 
    It is usually a good idea to scan through the  references given in 
letters before commenting.
    In this case see _http://physics.mercer.edu/hpage/compound/compound.html_ 
(http://physics.mercer.edu/hpage/compound/compound.html) 
    Professor Peters uses a capacitative position  detector with a DC output. 
This is sensitive to a much wider range of  signals than inductive magnetic 
detectors and can measure long period tilt  signals. He used a tuned detector 
to monitor storm background microseism  signals. 
 
    The current suggestion however, is to use your  Lehman effectively 
'tuned' at about 20 sec period to dig out small long period  seismic signals from 
the noisy background. Many of the regional Love and  Rayleigh waves are about 
this period - this is around the standard observing  window for measuring quake 
magnitudes with surface waves.
    If you then process the signal for power you should  get the envelope of 
the quake signal. Why you say that this is not useful event  information?  
 

I had a  brief look at it and couldn't find the referred mathematical 
processing needed  to extract the information on a now "super sensitised" detector.  
I can  only guess that this would be based on the natural decay of the signal 
if it  received a momentary stimulus compared to what was actually going  on.
Ian
    If you read the text carefully, you will see  Professor Peters' offer:-
 
    In the days before computers, undamped operation  was indeed ridiculous 
for those who wanted to see all the intricacies of arrival  time features 
governed by phase, etc.  But with a computer we  now have the ability to graph what 
is probably the single-most-important  feature (to one with a single 
instrument as opposed to an array of them) of what  the seismometer is telling us 
about the earth's motion - the POWER.  By  using the computer to compensate for 
the transfer function of the pendulum, one  can generate a reasonably good power 
spectral density no matter whether the  instrument is damped or undamped.  I 
will provide details on this  important calculation for those who are 
interested. 
 
    Regards,
 
    Chris Chapman






In a message dated 20/01/2007, Bobhelenmcclure@....... writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>
  
Hi all,
  
What Dr. Peters wants us to try left me stunned. All that will result=
 is=20
  a narrow-band modulated 20 Hz carrier without any useful event=20
  information.
  
Bob

Hi Bob,
 
    You mean 20 sec period ~ 0.05 Hz?
 
    It is usually a good idea to scan through the=20
references given in letters before commenting.
    In this case see http://physi=
cs.mercer.edu/hpage/compound/compound.html
    Professor Peters uses a capacitative position=20
detector with a DC output. This is sensitive to a much wider range of=20
signals than inductive magnetic detectors and can measure long period tilt=20
signals. He used a tuned detector to monitor storm background microseis=
m=20
signals. 
 
    The current suggestion however, is to use your=20
Lehman effectively 'tuned' at about 20 sec period to dig out small long peri=
od=20
seismic signals from the noisy background. Many of the regional Love and=20
Rayleigh waves are about this period - this is around the standard observing=
=20
window for measuring quake magnitudes with surface waves.
    If you then process the signal for power you sh=
ould=20
get the envelope of the quake signal. Why you say that this is not useful ev=
ent=20
information?  
 
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>I had a=20
  brief look at it and couldn't find the referred mathematical processing ne=
eded=20
  to extract the information on a now "super sensitised" detector.  I c=
an=20
  only guess that this would be based on the natural decay of the signal if=20=
it=20
  received a momentary stimulus compared to what was actually going=20
  on.
Ian
    If you read the text carefully, you will see=20
Professor Peters' offer:-
 
    In the days before computers, undamped operatio=
n=20
was indeed ridiculous for those who wanted to see all the intricacies of arr=
ival=20
time features governed by phase, etc.  But with a computer we=20
now have the ability to graph what is probably the single-most-importan=
t=20
feature (to one with a single instrument as opposed to an array of them) of=20=
what=20
the seismometer is telling us about the earth's motion - the POWER.  By=
=20
using the computer to compensate for the transfer function of the pendulum,=20=
one=20
can generate a reasonably good power spectral density no matter whether the=20
instrument is damped or undamped.  I will provide details on this=20
important calculation for those who are interested. 
 
    Regards,
 
    Chris Chapman