Thread: Calculating the CONSTANT to use to remove instument response

Started: 2009-04-08 23:50:56
Last activity: 2009-04-09 04:13:57
Topics: SAC Help
Hi All,
I am trying to remove instrument responses from STS_2, CMG3T. CMG_ES
broadband instruments. I got the poles and zeros from IRIS Pascal
Instrumentation. But I have difficulty figuring out what constant I should
use in the *.pz file that has to read by the SAC TRANSFER command. For
example, I was trying to synthesis a WA seismogram by removing the STS_2
response and convoulating the WA response. I used a constant of 1 in this
calcultion. The synthesis seismogrm looks good but the displacemnt values
don't make sense (they are several hunderd meters). I understand it is
because of the CONSTANT=1 I put. My Question is How can I calculate the
correct CONSTANT that I need to put with the zeros and poles in the SAC *.pz
file. The IRIS PASCAL instrumentation page gives the zeros and poles and a
normalization factor.
I greatly appreciate your help in this matter.

Melaku Bogale
New Mexico State University
Department of Physics
Las Cruces NM 88003-8001


  • Hello Melaku Bogale,

    You need to know the total sensitivity of the digitizer, this is the
    value which relates digital counts to ground units. The poles and
    zeros only represent the sensor. The CONSTANT in the SAC poles and
    zeros file should be the total sensitivity multiplied by the
    normalization factor for the poles and zeroes. The value for CONSTANT
    depends on the units desired also.

    Chad
    IRIS DMC

    On Apr 8, 2009, at 3:50 PM, Melaku Ayenew wrote:

    Hi All,
    I am trying to remove instrument responses from STS_2, CMG3T. CMG_ES
    broadband instruments. I got the poles and zeros from IRIS Pascal
    Instrumentation. But I have difficulty figuring out what constant I
    should use in the *.pz file that has to read by the SAC TRANSFER
    command. For example, I was trying to synthesis a WA seismogram by
    removing the STS_2 response and convoulating the WA response. I used
    a constant of 1 in this calcultion. The synthesis seismogrm looks
    good but the displacemnt values don't make sense (they are several
    hunderd meters). I understand it is because of the CONSTANT=1 I put.
    My Question is How can I calculate the correct CONSTANT that I need
    to put with the zeros and poles in the SAC *.pz file. The IRIS
    PASCAL instrumentation page gives the zeros and poles and a
    normalization factor.
    I greatly appreciate your help in this matter.

    Melaku Bogale
    New Mexico State University
    Department of Physics
    Las Cruces NM 88003-8001
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