Patent ID: 8289023

Claim:
A geophysical survey system comprising: a first sensor system including multiple magnetic field sensors for measuring magnetic field components of a low frequency magnetic field resulting from naturally occurring electromagnetic sources, the magnetic sensors of the first sensor system measuring magnetic field components representing three axes which are substantially perpendicular to each other; a second sensor system spaced apart from the first sensor system and including multiple magnetic field sensors for measuring magnetic field components of a low frequency magnetic field resulting from naturally occurring electromagnetic sources, the magnetic sensors of the second sensor system measuring magnetic field components representing two or three axes which are substantially perpendicular to each other; and a processing system for receiving information about the magnetic field components measured by the first sensor system and the second sensor system and in dependence thereon estimating transfer functions at a plurality of frequencies for transforming magnetic field components measured by the second sensor system to magnetic field components measured by the first sensor system, and computing parameters from the transfer functions that are independent of rotation of the first sensor system or the second sensor system about any axis thereof.