[MSNoise] Autocorrelations in MSNoise

[Thomas Lecocq]

Hi Christos,


Indeed, it's not yet implemented. I hope to have that soon...

Thomas


Le 26/05/2016 à 12:58, Christos Evangelidis a écrit :
> Hi Thomas,
>
> As far as I understand you haven't changed anything since then in the code
> concerning the pre-processing when computing autocorrelations. Right?
>
> Greetings from Athens,
>
> Christos
>
>
>
>
> From: Thomas Lecocq <thomas.lecocq at ...
> <http://gmane.org/get-address.php?address=thomas.lecocq%2d7ewb5K7nbqnl%2fIpH24cmtA%40public.gmane.org>
> Subject: Re: Autocorrelations in MSNoise
> <http://news.gmane.org/find-root.php?message_id=54DB931F.5080705%40seismology.be>
> Newsgroups: gmane.science.geophysics.msnoise
> <http://news.gmane.org/gmane.science.geophysics.msnoise>
> Date: 2015-02-11 17:36:31 GMT (1 year, 14 weeks, 6 days, 11 hours and 16
> minutes ago)
>
> Hello Aurélien,
>
> Le 11/02/2015 18:30, Aurélien Mordret a écrit :
>> Hi Thomas,
>>
>> What is the pre-processing of the noise when computing autocorrelations? Is
>> it the same as for the cross-correlations?
> Yeah, currently it's the same, WHICH IS NOT GOOD ! (that's why it's
> written somewhere NOT TO USE AUTOCORR), but that might not be trivial to
> find...
>
> Your suggestion makes absolutely sense ! Are you used to github etc ? If
> yes, please fork and PR an updated version of whiten ! (including a
> autocorr=False flag in the def, maybe?)!
>
> Regards from Brussels
>
> Thomas
>> If yes, would it be better to not fully whiten the data before
>> autocorrelation as the only information comes from the amplitude spectrum
>> (and not the phase)?
>>
>> I suggest to modify a bit the whiten.py function to keep the structure of
>> the whole code similar. Following Gorbatov et al. (2013), instead of
>> putting the amplitude spectrum =1 (with tapper) I would use a normalisation
>> with a water-level in the form
>>
>> A(freq) = A(freq)/max(A(freq),c*max(A(freq)))
>>
>> With A the amplitude spectrum and c the water-level factor (which is
>> typically on the order of 1%).
>>
>> It should not change the results for the cross-correlations and improve the
>> autocorrelations.
>>
>> Does it make sense or did I missed something?
>>
>> Cheers,
>>
>> Aurelien
>>
>> REF:
>>
>> Gorbatov, A., Saygin, E., & Kennett, B. L. N. (2013). Crustal properties
>> from seismic station autocorrelograms. *Geophysical Journal International*,
>> **192**(2), 861-870.
>>
> _______________________________________________
> MSNoise mailing list
> MSNoise at mailman-as.oma.be
> http://mailman-as.oma.be/mailman/listinfo/msnoise