PSN-L Email List Message

Subject: Re: Newbie trying to get started
From: ChrisAtUpw@.......
Date: Fri, 20 Jun 2008 18:02:27 EDT


In a message dated 2008/06/20, steinar@............. writes:

> Hello List,
> I'm in the process of setting up a seismometer.  I was considering a
> few options for building one based on internet descriptions, until I
> found the SEP seismometer which at =A3315 seemed likely to turn out
> cheaper than all parts needed to build one myself:=20
>=20
> http://www.mutr.co.uk/product_info.php?products_id=3D9047
>=20
> So I got this seismometer and a quick start.  I built a box for it,
> and I set up a datalogger.  For the datalogger I'm using a Linksys
> NSLU2 which is running SlugOS Linux.  It's a little box with a 266MHz
> ARM processor and 32 MB RAM, plenty for the task.  It has ethernet and
> two USB ports.  I've plugged a card reader into one port, to which
> I've connected two flash cards which makes up the filesystem
> configured as RAID 1 for added reliability, and the other is used to
> connect to the seismometer by a serial cable.
>=20
> So far, so good.  Now I only need to add some software.  I've searched
> a bit for existing software, but it turns out to be mostly Windows or
> DOS applications with no source code provided, which wont run on an
> ARM processor.  I think that to use a full blown leftover pc running
> Windows for the task is both impractical and expensive.  I guess I
> have to write some code myself.
>=20
> I wrote a small program which logs the data from the seismometer.  I
> currently plot what I get on this web page (using gnuplot):
>=20
> http://voksenlia.net/met/seismometer/
>=20
> What's remaining is some processing prior to plotting.  I most likely
> need to process my data with a lowpass filter.  But then I've run into
> a problem.  I know very little about signal processing, and I don't
> know what type of filter I should use for the best results.  Existing
> software uses filters it seems, but I haven't found any source code
> which could help me out.  So I turn to this list.
>=20
> I have a 16 bit A/D converter sampling at 20 Hz.  My seismometer has a
> natural period of about 16 seconds.  How should I process the data?

Hi Steinar,

       You seem to be trying to do things the hard way!

       The SEP box is designed to plug directly into almost any old PC=20
running windows! You download the AmaSeis data logging and analysis software=
 from=20
http://bingweb.binghamton.edu/~ajones/AmaSeis.html This gives you a WHOLE SU=
ITE=20
of dedicated seismic programs, including both low and high pass digital=20
filters, FFT analysis and a lot more! The hard work has already been done fo=
r you!

       It also contains the control program for the SEP ADC, which you have=20
to select on setup. It also supplies both screen and analysis display filter=
s.=20
The amplifier has an inbuilt low pass filter at 5 Hz, but it will handle=20
periods out to over 30 seconds. A lot of the surface Love waves peak at peri=
ods of=20
about 20 seconds. I can set the seismometer period to 20 seconds without any=
=20
problem.

       You may find it beneficial to run the drumplot screen display low pas=
s=20
filter set at about 10 seconds. This cuts out the ocean microseism backgroun=
d=20
at about 6 seconds and makes most quakes easily recognisable. You can then=20
extract a trace and analyse if for the P and S waves. If you input your own=20
station location at setup and know the initial earthquake time, you can disp=
lay=20
travel time curves on the analysis screen and match the two up!

       Regards,

       Chris Chapman  =20
In a me=
ssage dated 2008/06/20, steinar@............. writes:

Hello List,
I'm in the process of setting up a seismometer.  I was considering a few options for building one based on internet descriptions, until I
found the SEP seismometer which at =A3315 seemed likely to turn out
cheaper than all parts needed to build one myself:

http://www.mutr.co.uk/product_info.php?products_id=3D9047

So I got this seismometer and a quick start.  I built a box for it,
and I set up a datalogger.  For the datalogger I'm using a Linksys
NSLU2 which is running SlugOS Linux.  It's a little box with a 266MHz ARM processor and 32 MB RAM, plenty for the task.  It has ethernet and<= BR> two USB ports.  I've plugged a card reader into one port, to which
I've connected two flash cards which makes up the filesystem
configured as RAID 1 for added reliability, and the other is used to
connect to the seismometer by a serial cable.

So far, so good.  Now I only need to add some software.  I've sear= ched
a bit for existing software, but it turns out to be mostly Windows or
DOS applications with no source code provided, which wont run on an
ARM processor.  I think that to use a full blown leftover pc running Windows for the task is both impractical and expensive.  I guess I
have to write some code myself.

I wrote a small program which logs the data from the seismometer.  I currently plot what I get on this web page (using gnuplot):

http://voksenlia.net/met/seismometer/

What's remaining is some processing prior to plotting.  I most likely need to process my data with a lowpass filter.  But then I've run into<= BR> a problem.  I know very little about signal processing, and I don't
know what type of filter I should use for the best results.  Existing software uses filters it seems, but I haven't found any source code
which could help me out.  So I turn to this list.

I have a 16 bit A/D converter sampling at 20 Hz.  My seismometer has a<= BR> natural period of about 16 seconds.  How should I process the data?

Hi Steinar,

       You seem to be trying to do things the=20= hard way!

       The SEP box is designed to plug directl= y into almost any old PC running windows! You download the AmaSeis data logg= ing and analysis software from http://bingweb.binghamton.edu/~ajones/AmaSeis= ..html This gives you a WHOLE SUITE of dedicated seismic programs, including=20= both low and high pass digital filters, FFT analysis and a lot more! The har= d work has already been done for you!

       It also contains the control program fo= r the SEP ADC, which you have to select on setup. It also supplies both scre= en and analysis display filters. The amplifier has an inbuilt low pass filte= r at 5 Hz, but it will handle periods out to over 30 seconds. A lot of the s= urface Love waves peak at periods of about 20 seconds. I can set the seismom= eter period to 20 seconds without any problem.

       You may find it beneficial to run the d= rumplot screen display low pass filter set at about 10 seconds. This cuts ou= t the ocean microseism background at about 6 seconds and makes most quakes e= asily recognisable. You can then extract a trace and analyse if for the P an= d S waves. If you input your own station location at setup and know the init= ial earthquake time, you can display travel time curves on the analysis scre= en and match the two up!

       Regards,

       Chris Chapman

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