Thread: Removing Instrument Response

Hi,
Usually, in the rawest form (like the data you download from Wilbur), SAC
files are in counts, and not displacement. TRANSFER is used to convert
counts to displacement, velocity, or acceleration. The SAC manual is very
clear about FROM/TO function.

"The default input and output "instrument" in TRANSFER is displacement,
which in SAC is designated as NONE. Hence, if a FROM type or a TO type is
not specified, SAC assumes it to be NONE. If the output instrument is NONE,
IDEP in the SAC header is set to DISPLACEMENT (NM). For the seismometers
listed in the table below, the output units for TO NONE will be in nm,
SAC's choice for displacement. If TRANSFER has TO VEL or TO ACC, the header
variable IDEP is changed accordingly for all waveforms in memory."

If your SAC files are already displacement before applying TRANSFER, based
on the above, you set FROM NONE, which implies that your data do not
contain the instrument response to begin with.

Unless you are reading the headers wrong, here's what I would do to remove
the instrument response assuming that you have downloaded data as seed
volumes and that you have extracted response files using rdseed.

Output: displacement
TRANSFER FROM EVALRESP FNAME your_response_filename TO NONE FREQ f1 f2 f3 f4

If you have extracted pole-zeros files instead of response files, then
TRANSFER FROM POLEZERO SUBTYPE your_pole-zeros_filename TO NONE FREQ f1 f2
f3 f4

Where, f1, f2, f3, and f4 are frequencies (See SAC manual)

Januka.


Januka Attanayake
Postdoctoral Research Associate

Institut für Geophysik
Westfälische Wilhelms - Universität Münster
CorrensstraBe 24
48149 Münster
Germany

University email: jattanayake<at>uni-muenster.de
Homepage: http://sites.google.com/site/janukaattanayake/

On 12 May 2016 at 15:30, Narendra Pandey <nkpiitr<at>gmail.com> wrote:

Hello,
I am trying to remove instrument correction from seismogram (downloaded
through Wilber) using TRANSFER command. But, I am not able to figure out
the units. In SAC file the units are given in displacement by default, but
the response file units are generally reported in velocity units.
How the transfer command handle these units in FROM & TO options?

Thank you.
Narendra

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