[MSNoise] compute mwcs error

Mon Dec 20 07:42:09 UTC 2021

Hi Martha et al.,

By 1 day, I meant 1 week I guess. Sorry about that. Here are my notes from
Aurelien's original message about the FTAN parameters.

The bmin and bmax parameters are the bandwidth min and max of the
gaussian filters used in the FTAN algorithm.
The FTAN applies a set of Gaussian filters to the seismograms with
different central frequencies.
The width of the filter (in Hz) for the minimum central frequency is bmin
and vice versa for bmax.
The width for the intermediate filters increases linearly between bmin and
bmax.
So you can determine the beta for each central frequency (f) as, *beta =
linspace(bmin, bmax, nfreqs)*

These parameters are equivalent to the "alpha" parameters in this
paper defining the FTAN:
Herrmann, R. B. (1973). Some aspects of band-pass filtering of surface
waves. *Bulletin of the Seismological Society of America*, *63*(2), 663-671.

If you look into the cpp source code in libfta.cpp (starting at line 31)
you see the Gaussian filter definition.

*double filtre_Gaussien(double f, double fh, double beta){//printf("freq :
%f filtrage : %f beta : %f\n",f, fh, beta);return
1.0/beta*exp(-0.5*(f-fh)*(f-fh)/(beta*beta));}*

Keep in mind that in this msnoise-tomo case, alpha/beta changes with each
frequency. If I recall correctly, Aurelien's recommendation was to have the
bmin/bmax vary by orders of magnitude (e.g. bmin=0.03, bmax=3.0). I can't
find his email stating this or the reason, but this is what I recollect. If
you play with the values you will see how the bandwidth changes the
structure in the FTAN image. In the end, this changes how the autopicking
picks.

Please let me know if you have any other questions.

Dylan

On Wed, Dec 8, 2021 at 8:15 AM Dylan Mikesell <DylanMikesell at boisestate.edu>
wrote:

> Hi Martha,
>
> Yes, I do have some documentation about this. Give me a day to get it
> sorted out. My last two MS students wrote some things about this. It comes
> from the original papers that Aurelien Mordret wrote.
>
> Dylan
>
> On Wed, Dec 8, 2021 at 3:57 AM Martha Savage <martha.savage at vuw.ac.nz>
> wrote:
>
>> Dear Thomas,
>>
>> Can you tell us what stage your paper "Lecocq, T., Mordret, A. (in prep),
>> MSNoise-TOMO." Is in? We are trying to figure out how to use MSnoise-tomo
>> and are having trouble understanding what some of the parameters are and
>> therefore what would be good values to use.  We hope that some of the
>> answers might be in that paper.
>>
>> Otherwise, do you have any other documentation or hints?  Right now the
>> parameter we are most concerned with is the Gaussian filter bandwidth bmin
>> and bmax.
>>
>>
>> Thanks,
>>
>> Martha
>>
>> Martha Savage
>> Professor of Geophysics, SGEES
>> Victoria University of Wellington
>> Te Whare Wananga o te Upoko o te Ika a Maui
>> Cotton 529
>> Box 600, Wellington 6140
>> New Zealand
>>
>> Email: Martha.Savage at vuw.ac.nz
>> DDI: +64 (0)4 463-5961
>> Mobile: +64 (0)21-262-7516
>> Makere ana nga here
>>
>>
>> -----Original Message-----
>> From: msnoise-bounces at mailman-as.oma.be <
>> msnoise-bounces at mailman-as.oma.be> On Behalf Of Thomas Lecocq
>> Sent: Wednesday, 24 November 2021 8:53 PM
>> To: msnoise at mailman-as.oma.be
>> Subject: Re: [MSNoise] compute mwcs error
>>
>> Hi,
>>
>> This usually means that no points for computing the linear regression.
>> Did you set up a very very narrow filter, narrower than the number of
>> points available in the spectrum ?
>>
>> Thomas
>>
>> Le 23/11/2021 à 14:49, Michelle Lee a écrit :
>> > Hello everyone!
>> >
>> > Hope everyone is doing well! I ran into an error while trying to run
>> > compute_mwcs. I am not quite sure what the error fully means and was
>> > wondering if anyone could help me with the error or point me in the
>> > right direction to troubleshoot and resolve the error. Thanks!
>> > [image: Screen Shot 2021-11-23 at 8.43.25 AM.png] Best Wishes,
>> > Michelle Lee
>> > ----------------------------------------------------------------------
>> > ------
>> > Ph.D. Candidate
>> > Columbia University: Lamont-Doherty Earth Observatory Department of
>> > Earth and Environmental Science Marine Geology and Geophysics
>> > c: (206)397-2488
>> > alt. email: mkl2158 at columbia.edu
>> >
>> >
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