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BGS Global Geomagnetic Model

What is it?

The BGS Global Geomagnetic Model (BGGM) is a mathematical model of the Earth's magnetic field in its undisturbed state. It is revised every year to allow for the inclusion of new data collected since last revision and any development of the modelling methodology. With annual revisions it is also possible to minimise errors arising from predicting the field at some date after the time span of input data. In 2019 the maximum spherical harmonic degree increased from 133 to 1440. Degree 133, representing features of wavelength 300 km at the Earth's surface, is close to the maximum resolution that can be achieved with satellite data above 300 km altitude. By including information from near-surface total intensity anomaly compilations the theoretical resolution can be increased to 28 km.

What is it for?

The BGGM is widely used in the oil industry for directional drilling with Measurement-While-Drilling (MWD) magnetic survey tools. These tools measure the direction of the well-bore relative to the direction of the local geomagnetic field and are used to navigate wells towards precisely known underground targets. The local geomagnetic field is determined using the BGGM and the MWD data can then be used to give the drilling location in a geographic reference frame. An enhancement of this is to determine the local crustal field using either local absolute observations of the geomagnetic vector or transformation of local total intensity data collected during an aeromagnetic or marine survey. A further enhancement is to take account of the rapidly varying external field using nearby observatory data. These enhancements are referred to as In-Field Referencing (IFR)/IFR1 and Interpolation In-Field Referencing (IIFR)/IFR2 respectively.

How can I get it?

The model and associated software are available under licence from the BGS. Licence holders receive source code for incorporation into their own software throughout company, DLLs, Excel implementation examples, a Windows program for use throughout company, access to the web service and documentation.

Install BGGM Software and Model 2019

How accurate is it?

Scalable 1-sigma error estimates are output by all BGGM software. For BGGM2019 these estimates are derived from an update of the work presented at ISCWSA in March 2019. They combine errors from the unmodelled crustal field including effect of near-surface data coverage, unmodelled external field and core field prediction and are converted from XYZ to DIF taking account of main-field geometry.

Use the tool below to show estimated errors for the BGS Global Geomagnetic Model (BGGM) for a given set of coordinates and date. These are split into ISCWSA G and R for Global and Random errors which determine error propagation in industry models.

Either enter the geodetic latitude and longitude or simply click on the map. The date and depth may also be set.

Clicking on the 'Show result on map' button will display the values for the chosen coordinates in a pop-up window. These results may be saved by clicking on the 'Save' button allowing you to compare values from a number of locations.

As this is based on a web service you can also obtain results in XML, JSON or TXT format using an HTTP GET request
http://geomag.bgs.ac.uk/web_service/GMModels/bggmerr/current/?latitude=51.483&longitude=0&date=2019-10-23&format=xml
modifying the query string parameters as appropriate.

Geodetic Coordinates
(See note 1)
(See note 1)
km below MSL
Date
Legend
DECGMWD: Declination - Global
DECRMWD: Declination - Random
DBHGMWD: BH-Dependent Declination - Global
DBHRMWD: BH-Dependent Declination - Random
MDIGMWD: Magnetic Dip with Z-Axis Corr - Global
MDIRMWD: Magnetic Dip with Z-Axis Corr - Random
MFIGMWD: Total Magnetic Field with Z-Axis Corr - Global
MFIRMWD: Total Magnetic Field with Z-Axis Corr - Random

Please note that for Internet Explorer 10 and earlier there may be occasional erratic behaviour from the clickable map and the pop-up window. For very old versions of Internet Explorer the results may not be visible.

Earlier estimates are from peer-reviewed work in SPE paper 119851. That work used models of low resolution, i.e low spherical harmonic degree, so resulted in conservative, i.e. safe, error estimates.


For further information please contact us at: bggm@bgs.ac.uk.

Susan Macmillan - Project Leader