[OpendTect_Users] Topographic Adjustment

[Friso Brouwer]

Jason,

I am not hundred percent sure, but if I understand your problem
correctly you want to establish a common virtual recording surface
using your topography data, for example by applying a delay to your
traces at recorded at low elevation units. If that is indeed your
objective there is a simple workflow in OpendTect to do that.

1) Import your topography data as an OpendTect horizon*
2) Go to the attribute engine and:
2a) Use the Horizon attribute to extract your topographic Z.
2b) Use the mathematics attribute to convert your topographic Z to a
radar twt delay that can be used for the correction (I suppose you
would want to use the EM wave velocity of the top soil for that)
2c) Apply the calculated shift using the reference shift attribute.
Iterate with step 2b) to estimate the best correction factor.
3) Test on the fly if the shift realigns you data satisfactory.
4) If your QC is ok, then go to the processing menu to calculate and
store the shifted volumes.

* Be careful with the import of the topography as horizon. I assume
your topography is probably not measured in the same vertical quantity
and unit as your radar data (elevation in meter, versus twt in
microseconds) . Normally you would correct for that in step 2b, but
likely the dynamic range and resolution of the topographic elevation
is out of range with the survey set-up. That would probably result in
a failed import of the horizon and if this is the case you will need
to convert the elevation to radar twt units before importing the
elevation to OpendTect. You can use step 2b to make small adjustments.

Hope this helps.

Friso

-- 
Friso Brouwer
Support Americas
dGB Earth Sciences

+1 281 240 3939 (o)
support-americas at dgbes.com

On Wed, Apr 6, 2011 at 9:13 AM, Jason Herrmann <jherrma at uark.edu> wrote:
> Dear OpendTect Users,
>
> I am using OpendTect to display and analyze GPR data (dzt format) from
> an archaeological site where the terrain is far from flat and level.
> We did collect topographic data at the site with a total station, is
> there a way make the survey sections conform to the contours of
> surface topography in OpendTect?
>
> Best to all and thank you in advance for your response,
> Jason
>
> --
> Jason T. Herrmann
> Doctoral Candidate - Environmental Dynamics Program
> University of Arkansas
> Research Project Professional - Oriental Institute
> University of Chicago
>
> jherrma at uark.edu
> http://www.jasonherrmann.net
>
>
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