[SAC-HELP] polezero option

[Chad]

On Apr 26, 2009, at 6:26 AM, Arthur Snoke wrote:

> The polezero transfer functions are analog filters and in themselves  
> are causal.  The one I give as an example is an STS-2 response  
> function, which is mostly a damped harmonic oscillator.  (Aside: I  
> have read that there are three versions/generations of STS-2  
> seismometers, but so far as I can tell the analog-stage response is  
> always the same.  Can anyone clarify?)

Responding to the aside, there are 3 generations of electronics for  
STS-2s and three different sets of poles and zeros to represent them.   
To figure out which generation sensor you might have there are some  
general guidelines based on date of manufacture, but it remains  
possible that the electronics were upgraded if the sensor was returned  
to the factory.  The nominal responses for the 3 generations are  
available in SEED RESP format here:

http://www.iris.edu/NRL/sensors/streckeisen/streckeisen_sts2_sensors.html

The responses of the different generations only differ significantly  
at high frequencies.  I'm not quite sure how high is too high, I have  
heard 35Hz signals and above are where the differences between  
generations become significant.

To further complicate matters a "truncated" pole and zero response for  
STS-2s has been in common use for many years and it is different than  
any of the factory nominal responses.  It generally works fine for all  
the generations of sensors with the same caveat that it does not  
represent the sensor at high frequencies.

Apologies for the off topic message, seems like useful information to  
spread around.

Chad Trabant
IRIS Data Management Center