[SAC-HELP] Instrument response removal

[Arthur Snoke]

This is the correct address.  However, I cannot follow the logic in your 
message so (for me at least) you need to provide more information.

By construction, a pole-zero file is causal.  However, if you include with 
that step a "freqlimits" call, that call is not causal.  The number of 
poles for a p-z file depends on whether you are correcting to 
displacement, velocity, etc.  If your data came from a SEED volume, the 
RESP file makes clear what the correction is for.

For use to help, you need to provide more information.  If you have not 
already, I suggest you look at the transfer help file: 
<http://www.iris.edu/software/sac/commands/transfer.html>.

On Fri, 6 May 2011, Ivan Lokmer wrote:

> Dear Colleague,
>
> I hope that I am at the right address to launch my question.
> I was using SAC polezero option recently to remove the instrument response 
> from my data and to add it to synthetics.
> However, I realized that this option is acting as a 2-pass acausal filter. AS 
> the actual seismometer filters the ground motion as 1-pass causal filter, it 
> seems to me that it is impossible to recover actual ground motion by using 
> this option.
> It is not very obvious with very band limited data, but it is more than 
> obvious for the data with static shift, where the waveform is changed before 
> time 0 (which is impossible for any physical device including seismometer).
> Do you maybe know if there's any option in SAC that will add/remove 
> instrument's response as of the actual physical device (causally)?
>
> Thank you in advance for your answer
> A great job is done with all the manuals and software. Thanks for that
>
> Kind regards,
>
> Ivan
>
> -- 
> ______________________________________________
> Ivan Lokmer
> Seismology and Computational Rock Physics Lab.
> Geophysics Group School of Geological Sciences
> University College Dublin
> Belfield
> Dublin 4
> Ireland
>
> Phone: +353 1 7162079
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