[Users] phase spectrum in spectral analysis

[Friso Brouwer]

Dear Laurent,
>
> I have been lately testing the spectral decomposition tool in OD to 
> define and characterise various geobodies.
>
> Although good results in term of vertical thickness and lateral extent 
> assessment are obtained by analysing amplitude maps at given 
> frequencies, it is often mentioned in the literature the use of 
> spectral phase maps (additionally to spectral amplitude maps) to 
> further detect lateral discontinuities.
>
I know where you are referring to, there are several articles in 
literature using the phase component of spec decomposition as tool for 
stratigraphic and structural characterization. To answer your questions:
> 1) OD has this option, and if not, (as I am just a geologist)
-1- No OpendTect does not have that option. Of course the spectral 
decomposition being part of the open source base of the OpendTect system 
it should not be difficult to program this as an extension of the 
spectral decomposition, or possibly it has already be done by others in 
the OpendTect user base. If there are many other users who think this 
would be useful option please let us know and we will considered in our 
development. Everyone please feel free to share you thoughts...

>  2) computing an instantaneous attribute (ie phase) with the Spectral 
> Decomp attribute (at a given frequency) as an input.
>
This will not give the same (identical) results as taking the phase of a 
certain frequency in the decomposition.  We do have other methods which 
would give could  additional results for you goal of vertical thickness 
and lateral extent assessment. Most important:
- *instantaneous phase* of the original seismic: of course

- *the fingerprint attribute*: this attribute is very useful to estimate 
how far a certain user picked facies extends and if it is present in 
other areas on a horizon. The fingerprint attribute takes multiple 
attributes as input (for example multiple spectral decomposition slices, 
or instantaneous amplitude and phase) and then calculate the similarity 
of this vector of attributes with reference attributes extracted at a 
user defined location. End result is a map which show the similarity of 
each point with a user defined facies. For example, gradual changes in 
this similarity may indicated a gradual facies change, or change in 
thickness (for example a floodplain, or thinning fan), sudden changes 
may indicated sudden edges of the facies (for example incised channels) 
or faults. See for more information: 
http://www2.opendtect.org/rel/html/r2599.htm

- *waveform segmentation*, this is included in one of our commercial 
plugins (Neural Networks). Please review sections 4.1.2 
(http://www2.dgb-group.com/rel/html/dgb/c645.htm#AEN676) and 6.5 
(http://www2.dgb-group.com/rel/html/dgb/x1043.htm) in our manual for 
more information. This is one of the most powerful tools to pick up 
subtle changes in the waveform along a horizon, but requires a high 
quality horizon interpretation.

Kind regards,

- 
Friso GC Brouwer
Geoscientist

dGB-USA
One Sugar Creek Center Boulevard
Suite 935
Sugar Land, TX, 77478

Tel 281 240-3939 (main)
Tel 281 240-6957 (direct)
Fax 281 240-3944
e-mail friso.brouwer at dgb-group.com
http://www.dgb-group.com


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