[SAC-HELP] Transfer problem

[Philip Crotwell]

Hi

Responses are at best confusing, but you need to remember that the gain is
not just a value, it is a value at a particular frequency.

The last stage (stage zero) is supposed to be the overall gain and should
be the product of the gains at each stage, but only if the frequency of
each stage is the same. In this case the stage zero gain is +1.25829E+09,
but it is given at freq of 5e-2. The stage 1 gain is 1.5e3, but at a freq
of 1Hz. So to be proper, you must adjust the gain based on the poles and
zeros from 1Hz to 5e-2 Hz before you multiply. Looking at the response plot
here:

http://service.iris.edu/irisws/evalresp/1/query?net=ET&sta=CPCT&loc=00&cha=HHZ&time=2009-06-07T00:00:00&units=def&annotate=true&output=plot

it looks like 5e-2 is just barely beyond the flat part of the response,
which explains why evalresp says that the stage 1 gain is  1.369329E+03
instead of 1.5e3. It has rolled off just a bit at 5e-2 Hz compared to 1Hz
which is in the flat part of the response.

To be honest, I think that the mistake in this response is not in the gain
numbers, but rather in the frequency reported in the stage zero. It
probably should have the frequency in the stage zero as 1Hz instead of
5e-3Hz . So, likely in this case the 1.25829E+09 is the gain you want to
use even though evalresp complains.

Hope this helps,
Philip



On Thu, Feb 20, 2014 at 1:44 PM, Brian Savage <savage at uri.edu> wrote:

> Dear Blaine,
>
> This error is generated by evalresp.  You should be able to confirm this
> by running evalresp on your RESP file.
>
> For example
> % evalresp CPCT HHE 2010 001 0.001 20 -v -f RESP.ET.CPCT.HHE.2
> << EVALRESP RESPONSE OUTPUT V3.3.3 >>
>  WARNING (norm_resp): computed and reported sensitivities differ by more
> than 5 percent.
>  Execution continuing.
>  --------------------------------------------------
>   RESP.ET.CPCT.HHE.2
>  --------------------------------------------------
>   ET CPCT 00 HHE  2009,001,00:00:00 2011,026,00:00:00
>    Seed units: Velocity(in)->Counts(out)
>    computed sens=1.14868E+09 (reported=1.25829E+09) @ 5.00000E-02 Hz
>    calc_del=8.92261E-01  corr_app=8.92261E-01  est_delay=8.92261E-01
>  final_sint=0.01(sec/sample)
>       stage  1: LAPLACE     A0=6.259322E+08 NZeros=  2 NPoles=  5
> Sd=1.369329E+03
>       stage  2: GAIN        Sd=1.000000E+00
>       stage  3: FIR_SYM_1   H0=1.000000E+00 Ncoeff=  1 SamInt=1.953125E-06
> Sd=8.388610E+05
>       stage  4: FIR_SYM_2   H0=1.000000E+00 Ncoeff= 36 SamInt=1.953125E-06
> Sd=1.000000E+00
>       stage  5: FIR_SYM_2   H0=1.000000E+00 Ncoeff=  6 SamInt=1.562500E-05
> Sd=1.000000E+00
>       stage  6: FIR_SYM_1   H0=1.000000E+00 Ncoeff=  7 SamInt=3.125000E-05
> Sd=1.000000E+00
>       stage  7: FIR_SYM_2   H0=1.000000E+00 Ncoeff= 48 SamInt=6.250000E-05
> Sd=1.000000E+00
>       stage  8: FIR_SYM_2   H0=1.000000E+00 Ncoeff=126 SamInt=2.500000E-04
> Sd=1.000000E+00
>       stage  9: FIR_SYM_1   H0=1.000000E+00 Ncoeff=501 SamInt=5.000000E-04
> Sd=1.000000E+00
>       stage 10: FIR_SYM_1   H0=1.000000E+00 Ncoeff=501 SamInt=1.000000E-03
> Sd=1.000000E+00
>       stage 11: FIR_SYM_1   H0=1.000000E+00 Ncoeff=501 SamInt=2.000000E-03
> Sd=1.000000E+00
> --------------------------------------------------
> %
>
> Possibly someone at IRIS can comment on this further.  I think the first
> gain value is being modified due to a Analog PoleZero.
>
> Brian
> savage at uri.edu
>
> On Feb 18, 2014, at 4:57 PM, Blaine Bockholt (bbckholt) wrote:
>
> I am attempting to remove the instrument response of some data.  I
> downloaded the RESPFILE from IRIS and while using the evalresp option of
> transfer, I get the following error:
>
> "WARNING (norm_resp): computed and reported sensitivities[ET.CPCT.00.HHE]
> differ by more than 5 percent."
>
> I thought the final sensitivity at the end of the file is the product of
> all the different gain/sensitivities of each stage.  When I calculate it by
> hand, I get the sensitivity reported.  I am not sure where this error is
> coming from, nor I am sure how SAC calculates the sensitivity.  Thanks.
>
> Blaine
>
> Here is the command I use
>
> trans from evalresp fname ET.CPCT.resp to none freqlim 0.001 0.002 15 20
> _______________________________________________
> sac-help mailing list
> sac-help at iris.washington.edu
> http://www.iris.washington.edu/mailman/listinfo/sac-help
>
>
>
> _______________________________________________
> sac-help mailing list
> sac-help at iris.washington.edu
> http://www.iris.washington.edu/mailman/listinfo/sac-help
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.iris.washington.edu/pipermail/sac-help/attachments/20140220/feef75d7/attachment.html>