[MSNoise] Autocorrelations in MSNoise

[Thomas Lecocq]

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.
>