Earth's Field

GM-SYS Profile Modelling requires the magnitude and orientation of the Earth's field at the location and time of the survey you are trying to model, in order to calculate the magnetic response correctly. Models that have zero for the Earth's field magnitude will be prompted to enter a value each time the model is loaded, unless you opt to turn off the warning.

It is possible to get a response with a field magnitude of zero, but an orientation defined, if any blocks in the model have remanent magnetization specified.

Use the IGRF at a Point GX (geogxnet.dll(Geosoft.GX.Igrf.Igrfpt;Run)) to determine the magnitude and direction of the Earth's field at the location of your survey.

Magnitude, H	Enter the magnitude of the field, in the specified units. Units may be changed in the Display menu.
Inclination, FI	Enter the inclination of the Earth's field, in degrees from horizontal.
Declination, FD	Enter the declination of the Earth's field, in degrees from True North.
Calculate	This button launches the IGRF at a Point GX, which enables you to calculate the Earth's field components from the latitude, longitude, elevation, and date of your survey.