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British Geological Survey Global Geomagnetic Model (BGGM) Uncertainties
 
The paper, SPE/IADC 119851 'Confidence Limits Associated with Values of the Earth's Magnetic Field used for Directional Drilling', described updated uncertainties for use with predicted geomagnetic parameters from the BGGM based on low to medium resolution BGGMs (maximum spherical harmonic degrees 13-30). 
 
Copies of the paper peer reviewed paper SPE 119851 are available from the SPE.
 
The results of the study included look-up tables arranged by geographic latitude and longitude for each confidence level. The associated confidence limit tables are available in the files below:
 
 
 Confidence LevelFile Name
1

68.3% 

BGGM68p3conflim.dat

2

 90%

BGGM90p0conflim.dat 

3

 95%

BGGM95p0conflim.dat 

4

 95.4%

BGGM95p4conflim.dat 

5

 99%

BGGM99p0conflim.dat 

6

 99.7%

BGGM99p7conflim.dat 

 
 
 

Reference:
 
SPE 119851, "Confidence Limits Associated With Values of the Earth's Magnetic Field Used for Directional Drilling", Susan Macmillan, British Geological Survey; and Steve Grindrod, Copsegrove Developments Ltd; SPE Drilling & Completion, 25(2), 230-238. DOI: 10.2118/119851-PA