PSN-L Email List Message

Subject: SAC binary file headers
From: "rem11560@............
Date: Mon, 7 Feb 2005 02:29:58 GMT

Hi all,

  I occasionally download SAC binary event files from the IRIS web site, primarily to compare my waveforms with that recorded by the nearby PAL and FOR stations of the LDEO network. I then use WinQuake to convert them to PSN format.

  In an effort to understand and use the information contained in the SAC header, I wrote a utility that reads out the 133 elements of the header. Not many of these elements contain any information on a typical file, but there is still a lot of information that is not transferred by WinQuake to the converted PSN file, including event time and location and sensor calibration. Event time is not specifically given, but is given as an offset in seconds from the starting time of the file.

There is a number in the SAC header labeled "SCALE", usually a very large number, which must have to do with the gain of the sensor. Can anyone explain to me how to use this number to calculate a number to enter in WinQuake for sensor sensitivity?  I have come up with an empirical formula

  Sensitivity = 40 * (1.0 / SCALE)

which seems to come close to what gives me the response I expect from PAL and FOR, based on my own outputs, but a formula like that really doesn't make much sense to me.  I hope someone out there can explain the meaning of SCALE.



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