[Users] Get traces features (mean, RMS, max) in OpendTect and restore bias when performing Frequency filtering

[Arnaud Huck]

Dear OpendTect users,
It is sometimes useful to have access to the mean, RMS or maximum of 
each trace, and this at each sample location.
Thanks to the new scaling attribute this is now possible. In order to do 
this, you first have to set a scaling attribute, type "window", basis 
"mean" for example, and as a time gate select to time of the first 
sample as "start" and the time of the last one as "stop". This attribute 
will then return you the mean of each trace, available at each sample 
location.

These useful feature can for example be used to restore the bias when 
performing frequency filtering. Indeed, in order to avoid getting a huge 
zero frequency component, the bias is removed in OD before computing the 
FFT. This is not necessary a problem when you are working with seismic 
volumes, but it is much more problematic if you want to filter an 
acoustic impedance cube, which is always positive and with large values.
You can avoid this very easily.
By assuming you want to filter x0=AI(t), set a first attribute in 
"mathematics" as your signal AI(t) subtracted by x1=the mean of AI(t). 
Then you can do the frequency filtering over this new input x0*(1-1/x1), 
lets call it x2. At the end, you just have to restore the mean of your 
signal in order to get your filtered AI(t) = x2+x0/x1.

If you have any questions do not hesitate to ask me.

Best Regards,
Arnaud Huck.

 
-- dGB Earth Sciences B.V.
-- Nijverheidstraat 11-2, 7511 JM Enschede, The Netherlands
-- mailto: arnaud.huck at dgb-group.com, http://www.dgb-group.com
-- Tel: +31 53 4315155 , Fax: +31 53 4315104