Choice of Forward Operator

[gabrahamastro]

I've recently been doing some 3D magnetics modelling and have been trying to work out what considerations should be made when choosing the forward operator using the cmp variable in the MagneticsModelling function. I've had a look at Holstein et al. (2007) but can't seem to see clear definitions of the various forward operators listed (TFA, Bx, By, Bz) are defined, and therefore how they should be chosen. I assume Bx, By and Bz are the three components of the magnetic field anomaly, whilst TFA is the combined effect?

Please could someone let me know whether I've understood this correctly and if there is a good method to decide which is most suitable.

[halbmy]

Yes, as the documentation
https://www.pygimli.org/pygimliapi/_generated/pygimli.physics.gravimetry.html#pygimli.physics.gravimetry.MagneticsModelling
says, there is (apart from the full tensor elements) the three components Bx, By and Bz of the anomaly, and the total field anomaly (TFA), which is NOT the square root of the three components but the change in the total field, i.e.

$$TFA = \sqrt{(Bx+X)^2+(By+Y)^2+(Bz+Z)^2}-\sqrt{X^2+Y^2+Z^2}$$

where X, Y, Z are the components of the Earth's field provided by the IGRF argument.