Thread: spectrogram questions

We can still output the spectrogram result with the "write sac output.sac"
command as a 3D XYZ file. After reading this xyz file in SAC, the "contour"
and "image" commands can be applied accordingly.

Wen-Tzong Liang




George Helffrich <george<at>elsi.jp> 於 2018年5月17日 週四 下午11:29 寫道：

Dear All -

It appears that the XYZ spectrogram option disappeared at some point from
the SAC version distributed by IRIS, which thwarts quantitative comparison
with alternative spectrogram calculation methods. Hence, I must add the
disclaimer that the comments apply to the SAC version described in the SAC
book. Sorry for any confusion.

On 17 May 2018, at 23:50, Aaron <aaronmoya<at>gmail.com> wrote:

Dear George:

I was just looking at the answer given to Mar Tapia and wanted to try the
command. However, I got an error when I used XYZ option. This is SAC
version 101.6.

SEISMIC ANALYSIS CODE [06/12/2013 (Version 101.6)]
Copyright 1995 Regents of the University of California

SAC> FUNCGEN SEISMOGRAM
SAC> SPECTROGRAM XYZ
ERROR interpreting command: SPECTROGRAM XYZ
ILLEGAL OPTION: ^


Aaron

On Wed, May 16, 2018 at 10:29 PM, George Helffrich <george<at>elsi.jp>
wrote:

Dear All -

1) The SPECTROGRAM results may be obtained from SAC by using the XYZ
option. This leaves the result in an XYZ file in memory that may be
written out and read by an auxiliary program for subsequent processing (or
plotting). The SAC XYZ file format is documented in online sources and in
Chapter 2 of the SAC book. The online resources associated with the book
contain example code that writes and, I think, reads SAC XYZ files.

2) You can use the COLOR command to define an alternate color palette
that will also be used in the color bar. See the COLOR RASTER command in
Chapter 10 of the SAC book for an example. Different versions of SAC might
not have the same set of built-in color maps available, however.

With some effort, you can design and plot your own color bar by making a
composite plot and plotting the color bar as a separate XYZ file. See
Chapter 7 of the SAC book for an introduction to composite plots.

3) Not being a MATLAB user I can’t comment on differences in the
appearance of any spectrograms that it calculates compared to SAC.

On 10 May 2018, at 21:18, Mar Tapia <mar.tapia<at>gmail.com> wrote:

Hi,

I have some questions related to spectrogram function in sac:

1. How can I save the results from spectrogram function in order to plot
with other softwares?

2. And is it possible to control the colorbar values in some way?

3. I don't understand why the spectogram plot using PSD method is so
different from the spectrogram function in matlab using same window length.
Is there any smooth or ponderation in the final results in order to show
better singularities or important zones?

Thanks in advance,

Mar



--
-----------------------------------------------------------
Mar Tapia

mar.tapia<at>gmail.com
------------------------------------------------------------

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George Helffrich
george<at>elsi.jp



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--
Aarón Moya
Laboratorio de Ingeniería Sísmica
Instituto de Investigaciones en Ingeniería
Universidad de Costa Rica
San José, COSTA RICA
Tel: 2253-7331 Fax: 2224-2619
http://www.lis.ucr.ac.cr

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George Helffrich
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