[SAC-HELP] SAC/SACA file format verification

[George Helffrich]

Dear Dan -

	This will be a very useful SeisMac feature.  There are two minor 
problems with the specimens that you provided:

	1) Undefined character values in the binary file should be padded with 
blanks, not trailing zero characters, to their field lengths (8 or 16 
characters, as appropriate);

	2) Undefined values should numerically be -12345.00 in the 
alphanumeric file.

Something else you might think about are:

	3) I think that you can safely set IDEP to IACC (integer number 8) to 
signify that the dependent variable is acceleration.

	4) The component naming fields KCMPNM for the traces don't follow FDSN 
standards.  (See Appendix A of the SEED manual).  My reading of the 
manual suggests that, for the sample rate shown, the channels should be 
named with three-letter codes BNx, where x is the orientation letter.  
N (middle character) is the code for an accelerometer.  ZNE aren't 
useful because orientation can't be guaranteed.  XYZ are probably OK 
for consistent usage with your program documentation, though they 
aren't FDSN-endorsed.  FDSN would prescribe them to be 123 (orthogonal 
but orientation not guaranteed).

On 28 Mar 2009, at 01:44, Daniel Griscom wrote:

> Dear Sirs/Madams,
>
> I'm the author of a free IRIS-supported Macintosh program called 
> SeisMac, which uses Mac laptops' built in accelerometers to convert 
> the laptops into (not very accurate) seismographs. You can find more 
> about it at <http://www.suitable.com/tools/seismac.html>.
>
> I'm finishing off an update which will let you export selected data as 
> a binary SAC or ascii SACA file. I think I've got it right (Global 
> Earthquake Explorer successfully reads the SAC files), but I'd love to 
> have further confirmation. Would any of you be able to review example 
> files and tell me if I've made any format errors? Or, point me to 
> other tools which will read/validate SAC/SACA files?
>
>
> I've uploaded the same set of data in three ways:
>
> - Comma-separated values (all three axis): 
> <http://www.suitable.com/temp/SeisMacData.CSV>
>
> - Binary SAC file (Z axis only): 
> <http://www.suitable.com/temp/SeisMacData.SAC>
>
> - Ascii SACA file (Z axis only): 
> <http://www.suitable.com/temp/SeisMacData.SACA>
>
> (If you have a Mac laptop and would like to play with exporting data 
> yourself, the latest binary is at 
> <http://www.suitable.com/temp/SeisMac30b2.zip>)
>
>
> Thanks,
> Dan
>
> -- 
> Daniel T. Griscom             griscom at suitable.com
> Suitable Systems              http://www.suitable.com/
> 1 Centre Street, Suite 204    (781) 665-0053
> Wakefield, MA  01880-2400
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                                     George Helffrich
                                     george at geology.bristol.ac.uk