What is accuracy with which the depth of cover over a pipeline can be
determined by measuring the field strength of the earth's magnetic
field in gamas along a line that extends within fifty feet over and
approximately perpendicular to the pipeline at positions recorded to
within 1cm rms in latitude, Longitude and elevation.

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Request for Question Clarification by larre-ga on 16 May 2002 08:14 PDT

Could you define some of the variables?

Specific type or brand/model of magnetometer
Magnetometer calibrated to what? when?
Composition of pipeline material
Composition of soil above the pipline and in the surrounding areas
Notable ferritic geologic structures in the area
Date and time measurements were taken (to be cross-checked against
sunspot activity)

Thanks - larre-ga

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Request for Question Clarification by chromedome-ga on 16 May 2002 17:18 PDT

On land, or offshore?

It appears that the accuracy of depth cover is within a 3.5-4 percent
error range according to an article in Pipeline and Gas Journal August
2000. This article spoke of a method of magnetizing the ocean floor
pipelines to gain that amount of accuracy. This method appears to work
very well with the stainless steel flexible submarine flow lines,
primarily used in areas that are too hazardous for tradition welded
pipelines system stretching across harsh environments, rough seas and
constantly changing ocean floor structures.

You can find the article in PDF format here :
www.innovatum.net/articles/August%20Pipeline%20&%20Gas%20Journal.pdf 

Another article I found very interesting regarding the use of this
technology to accurately map out archeological digs such as a Roman
city in England can be found here:

http://physicsweb.org/article/world/13/5/10


Another PDF paper, probably more interesting to you, which discusses
the means and methods of searching the sea floors for buried objects
and the physics behind a magnetometer, can be found here :

www.marinemagnetics.com/pdfs/SeaSPY_Tech_Guide.pdf 

I have an email posted to the author of this paper asking your
question specifically. He has yet to respond (and its been a while
now), but if he does I'll post his answer here as a clarification.

I hope this answers your questions and please don't hesitate to ask
for clarification if you require it.

webadpet-ga

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Request for Answer Clarification by haroldo-ga on 21 May 2002 14:35 PDT

Can you find an mathmatical error budget for positioning, size and
thickness of welded steel pipe, azimuth and declination of the earth's
magnetic field, distance from the pipeline, sun spot effect?

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Clarification of Answer by webadept-ga on 21 May 2002 22:08 PDT

I found several sites which may give you the rest of the answers you
are seeking, and I'm sure that you will find them interesting, and
possibly lead you the rest of the knowledge you are seeking.

Links :

Solar Magnetism Initiative 
http://www.hao.ucar.edu/smi/

UXO DISCRIMINATION AND IDENTIFICATION USING MAGNETOMETRY
http://www.geop.ubc.ca/ubcgif/pubs/papers/billings_uxo_discrim_mag.pdf

Modelling of attitude error in vector magnetic data: application ... 
http://www.gfz-potsdam.de/pb2/pb23/GeoMag/research/holme/EPS0534.pdf 

I hope this answers the rest of your questions and if you find you
need more I'll certainly try to provide it for you.

webadept-ga

Excellent research of historical experience with a direct answer.  An
explanation of the mathmatical error budget would have won him a
"*****".