Thread: BBFK alphanumeric output from SAC

Dear All -

This is one of the darker areas of SAC (in the sense of
documentation). The reference cited in the code for the method is
this:

Nawab, SH, FU Dowla, and RT Lacoss, Direction determination of wideband
signals, IEEE Trans. Acous. Speech Sig. Proc., 33: (5), 1114-1122,
1985.

The WAVENUMBER parameter is a value in reciprocal kilometers, and is
the maximum value that defines the extent of the X-Y grid of returned
values.

Assuming familiarity with reading SAC XYZ files, the value at every
spatial point should be the F-K value, transformed by the method
chosen: MLM, Music or PDS. MLM and Music will transform the F-K value
to its reciprocal on output. PDS does no transformation.

On 13 May 2009, at 21:04, Bob Myhill wrote:

Dear all,

I've been trying for some time to plot bbfk data retrieved from SAC
(the 09/04/2008 version) in .a format, but do not understand the
structure of the data output.

The SAC manual informs me that the data is output in 'square mode',
but I don't know how this relates to the azimuth and wavenumber, and
how consecutive data points are chosen. I've tried both a simple
azimuthal and wavenumber progression (rotating around the z-axis or
radiating from it) but neither of these seem to recreate SACs own
output.

Could you give me some advice on how to read this data?

Many thanks,
Bob

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George Helffrich
george<at>geology.bristol.ac.uk