Thread: FAP vs EVALRESP in SAC-101.4

Started: 2011-06-29 21:18:34
Last activity: 2011-06-29 23:53:51
Topics: SAC Developers
George Helffrich
2011-06-29 21:18:34
Dear All -

(I resending this to the sac-dev list after de- and re-registering). This is a separate topic to the FAP behavior that Sheila Peacock was requesting, hence a different message thread. It was prompted by the exchange on that topic, so while appearing similar is a different question.

Here's the question: If EVALRESP produces and handles FAP responses, what is the added functionality of TRANSFER SUBTYPE FAP? It seems that there are two mechanisms to achieve the same response correction, one especially built into SAC and the other built into EVALRESP (and implicitly used by SAC).

I could rationalize this if the FAP file format was different. I implemented FAP in MacSAC based on the documented specification of a pIDC FAP file. However SAC2000 seems to have abandoned this format (or at least stopped documenting it), so has lost this particular justification.

Hence the question about added functionality. Any enlightenment?

George Helffrich
george.helffrich<at>bris.ac.uk




  • Arthur Snoke
    2011-06-29 23:53:51
    George,

    First off, I got your message twice, the one to which I am replying came
    about 40 minutes later. I did not get a copy from [sac-dev] to my first
    message to Sheila, but I looked in the archives and it was there. I think
    I have gotten copies of subsequent messages sent to the listserv.

    Next: the SAC distributed through IRIS is not SAC2000, and I am not sure
    when you refer to SAC2000 which program is being referenced. The FAP got
    dropped in the transition to IRIS/SAC I think because the way it was
    written it was part of a bigger package that Someone decided to drop.

    As of the current version, EVALRESP produces FAP files. Earlier versions
    had FA and FP files, and this one combined them. We used the EVALRESP
    convention rather than the old one to which you refer for compatibility.
    Besides, it is a simpler format.

    EVALRESP does not apply FAP files to do instrument corrections, it just
    produces the file. As discussed in the current TRANSFER help file, an
    advantage of either using a FAP file produced by EVALRESP or by using
    EVALRESP within the TRANSFER command is that the response includes all the
    stages documented in the RESP file, whereas a POLEZERO subcommand includes
    only the first stage. However, running EVALRESP separately allows one to
    select the stages to include and provides flexibility about the frequency
    band, so a FAP file produced by EVALRESP can refine the instrument
    correction more than simply running TRANSFER in SAC with the EVALRESP
    subcommand.

    Sheila's research uses FAP files, and as of version 101.4 she can now run
    these within SAC. Maybe not totally to her liking, but before this
    version it was not an option in SAC. As you probably know, 30 years ago I
    used FAP files to deal with instrument corrections for broadband
    seismomenters recorded on magnetic tape. Also, Martin Chapman and I
    developed a procedure to do instrument corrections of network data
    transmitted over phone lines and we used FAP files.

    Let me know if I have not dealt adequately with your questions/comments.

    I am sending this at 16:53 EDT.

    Arthur

    On Wed, 29 Jun 2011, George Helffrich wrote:

    Dear All -

    (I resending this to the sac-dev list after de- and re-registering).
    This is a separate topic to the FAP behavior that Sheila Peacock was
    requesting, hence a different message thread. It was prompted by the
    exchange on that topic, so while appearing similar is a different
    question.

    Here's the question: If EVALRESP produces and handles FAP responses,
    what is the added functionality of TRANSFER SUBTYPE FAP? It seems that
    there are two mechanisms to achieve the same response correction, one
    especially built into SAC and the other built into EVALRESP (and
    implicitly used by SAC).

    I could rationalize this if the FAP file format was different. I
    implemented FAP in MacSAC based on the documented specification of a
    pIDC FAP file. However SAC2000 seems to have abandoned this format (or
    at least stopped documenting it), so has lost this particular
    justification.

    Hence the question about added functionality. Any enlightenment?

    George Helffrich
    george.helffrich<at>bris.ac.uk

23:51:34 v.ad6b513c