In a message dated 2007/04/24 03:19:37 GMT Daylight Time, 
Bobhelenmcclure@....... writes:


> Subj:Inverse filter for seismic sensors. 
> Date:2007/04/24 03:19:37 GMT Daylight Time
> From:Bobhelenmcclure@.......
> Reply-to:psn-l@..............
> To:psn-l@..............
> CC:E.Wielandt@............ bhutt@......... jimo17@......... rwsell@......... 
> mariotti@.......... jclahr@..............
> Sent from the Internet 
> 
> 
> 
>   I am an amateur seismographer, located in Locust Valley, NY. My station 
> consists of home built sensors of rather short natural period. Out of 
> necessity, I have developed a digital inverse filter, which allows extension of the 
> natural period of the sensors to five or more times their natural period. It 
> took a lot of grunting and straining to perfect this filter, and I want to 
> share it with anybody who could benefit. It ended up being simple to code and 
> use. All you need to set it up is the natural period and damping of the sensor, 
> and the desired filter period. It can be used in real time or on completed 
> files.
>  
>   In case you have any need to enhance the performance of geophones or any 
> other open loop sensor you operate, please refer to web page 
>  
>   http://www.jclahr.com/science/psn/mcclure/filter.html
>  
>   This page describes the analog prototype of the filter and the pseudocode 
> for its digital version. A mathematical analysis demonstrates that the 
> filter's frequency response is correct.
>  
>   This filter is implemented in my programs "WQFilter.exe" and 
> "Heliplot.exe", which can be downloaded from
>  
>   http://www.jclahr.com/science/psn/mcclure/wdq_utilities/index.html
>  
>   "WQFilter.exe" is a utility program for filtering WinQuake PSN Type 4 
> event files. "Heliplot.exe" is a program for filtering and displaying Dataq WQD 
> format files. It would be easy for me to code these applications for other 
> file formats, including Little Endian SAC binary files.
>  
>   Dr. Alan Jones has also incorporated this filter into "AmaSeis.exe" for 
> filtering SAC binary format event files. However, the version he has coded is 
> no longer up-to-date, and the response is not quite so accurate as the latest 
> version.
>  
>   All my applications are written using Visual Basic 6.0 for Windows. Alan 
> is currently re-coding Amaseis using Java, so that it can be compiled for 
> other operating systems.
>  
>   Please note that "WQFilter.exe" also includes Butterworth filters for 
> lowpass and highpass filtering. Forward, backward, and forward-backward filtering 
> can be selected. If you apply both my period extending filter and a second 
> order highpass backward filter to the event data, you can end up with a 
> broader bandwidth file which has no phase distortion and no time delay in the 
> passband.
>  
> Robert (Bob) McClure
> 
> 
> 
> See what's free at AOL.com. 
> 

   
In a me=
ssage dated 2007/04/24 03:19:37 GMT Daylight Time, Bobhelenmcclure@....... w=
rites:





Subj:Inverse filter for seis=
mic sensors. 

Date:2007/04/24 03:19:37 GMT Daylight Time

From:Bobhelenmcclure@.......<=
BR>
Reply-to:psn-l@..............
To:psn-l@..............

CC:E.Wielandt@..........., bhutt@........, jimo17@........, rwsell@usg=
s.gov, mariotti@........., jclahr@..............

Sent from the Internet 







  I am an amateur seismographer, located in Locust Valley, NY. My stati=
on consists of home built sensors of rather short natural period. Out of nec=
essity, I have developed a digital inverse filter, which allows extension of=
 the natural period of the sensors to five or more times their natural perio=
d. It took a lot of grunting and straining to perfect this filter, and I wan=
t to share it with anybody who could benefit. It ended up being simple to co=
de and use. All you need to set it up is the natural period and damping of t=
he sensor, and the desired filter period. It can be used in real time or on=20=
completed files.

 

  In case you have any need to enhance the performance of geophones or=20=
any other open loop sensor you operate, please refer to web page 

 

  htt=
p://www.jclahr.com/science/psn/mcclure/filter.html

 

  This page describes the analog prototype of the filter and the pseudo=
code for its digital version. A mathematical analysis demonstrates that the=20=
filter's frequency response is correct.

 

  This filter is implemented in my programs "WQFilter.exe" and "Heliplo=
t.exe", which can be downloaded from

 

  http://www.jclahr.com/science/psn/mcclure/wdq_utilities/index.html=


 

  "WQFilter.exe" is a utility program for filtering WinQuake PSN Type 4=
 event files. "Heliplot.exe" is a program for filtering and displaying Dataq=
 WQD format files. It would be easy for me to code these applications for ot=
her file formats, including Little Endian SAC binary files.

 

  Dr. Alan Jones has also incorporated this filter into "AmaSeis.exe" f=
or filtering SAC binary format event files. However, the version he has code=
d is no longer up-to-date, and the response is not quite so accurate as the=20=
latest version.

 

  All my applications are written using Visual Basic 6.0 for Windows. A=
lan is currently re-coding Amaseis using Java, so that it can be compiled fo=
r other operating systems.

 

  Please note that "WQFilter.exe" also includes Butterworth filters for=
 lowpass and highpass filtering. Forward, backward, and forward-backward fil=
tering can be selected. If you apply both my period extending filter and a s=
econd order highpass backward filter to the event data, you can end up with=20=
a broader bandwidth file which has no phase distortion and no time delay in=20=
the passband.

 

Robert (Bob) McClure







See what's free at AOL.com.