Thread: Removing instrument response

Started: 2016-03-07 18:30:24
Last activity: 2016-03-08 02:18:11
Topics: SAC Help
Abhash Kumar
2016-03-07 18:30:24
Hi,
I have SAC files (attached example) and the waveform look like velocity
signal, but the sac header shows the physical unit of displacement in
nanometer (with IDEP=6). This discrepancy is perhaps due to extracting the
sac files directly from the miniseed file that does not contain any
information about the physical unit. I am wondering to use "Transfer"
function of sac to remove the instrument response and get the real ground
velocity (nanometer/second). I have the response file (attached) obtained
from SEED volume using RDSEED. Can I use the transfer function as below:

SAC> r 2012.115.10.30.GREEN.EHE.SAC
SAC> RTR
SAC> TAPER
SAC> TRANS FROM EVALRESP FNAME RESP.GC.GREEN..EHE TO VEL FREQLIM 0.001
0.002 48 96

According to the SAC manual, TO instrument should be set to NONE to remove
the instrument response. As I want the ground velocity estimate, should I
set TO instrument to VEL or NONE. I would be extremely grateful for any
suggestion.

Best regards
Abhash Kumar

  • Milton Plasencia
    2016-03-08 02:18:11
    Hi Abhash,
    I saw your data, miniseed and sac initially have digital counts, when you applied
    the transfer is to convert digital counts and to obtain physical units.
    The data have sampling rate of 200 Hz.
    i use the read, rmean and finally transfer command.
    When you said TO NONE it means output in displacement, TO VEL obviously in velocity.
    Then your freqlimits should be revisited, your filter is 1000 500 sec!!, have a broad band sensor
    to cover up to this band?.
    Using this command transfer
    trans from evalresp fname RESP.GC.GREEN..EHE to vel freqlimits 0.05 0.1 20 50

    I obtain:




    So, you can replay to adjust the frequencies.

    HTH,

    Milton


    On Mar 7, 2016, at 16:30, Abhash Kumar <abhash.kumar84<at>gmail.com> wrote:

    Hi,
    I have SAC files (attached example) and the waveform look like velocity signal, but the sac header shows the physical unit of displacement in nanometer (with IDEP=6). This discrepancy is perhaps due to extracting the sac files directly from the miniseed file that does not contain any information about the physical unit. I am wondering to use "Transfer" function of sac to remove the instrument response and get the real ground velocity (nanometer/second). I have the response file (attached) obtained from SEED volume using RDSEED. Can I use the transfer function as below:

    SAC> r 2012.115.10.30.GREEN.EHE.SAC
    SAC> RTR
    SAC> TAPER
    SAC> TRANS FROM EVALRESP FNAME RESP.GC.GREEN..EHE TO VEL FREQLIM 0.001 0.002 48 96

    According to the SAC manual, TO instrument should be set to NONE to remove the instrument response. As I want the ground velocity estimate, should I set TO instrument to VEL or NONE. I would be extremely grateful for any suggestion.

    Best regards
    Abhash Kumar
    <2012.115.10.30.GREEN.EHE.SAC><RESP.GC.GREEN..EHE>


07:29:06 v.01697673