Data acquisition system

An induced polarisation (IP) data acquisition system for deriving geological survey data that is indicative of one or more geophysical properties of an opaque first geological body, the system including:

• a first plurality of measurement nodes located at or adjacent the surface of the earth and adapted to obtain a plurality of measurement signals indicative of the electric field strength at a corresponding plurality of spaced apart locations at or adjacent to a surface of said first geological body, in response to an electrical input current signal injected via electrodes into the first geological body, wherein the plurality of measurement signals are synchronised among each other;
• a reference node located at or adjacent the surface of the earth and adapted to obtain reference signals indicative of the magnetic field strength at a location at or adjacent to a surface of a second geological body that is spaced apart from the first geological body, in response to the input current signal injected into the first geological body, wherein the reference signals are synchronised with the measurement signals;
• and
• a processing centre being responsive to the measurement signals and the reference signals for deriving a transfer function for the first body, said system being adapted to identify geophysical properties below the surface of the earth;
• wherein a predicted noise signal is determined by applying the transfer function to measurement signals and reference signals that are subsequently obtained in the presence of a current signal in the first geological body, where the predicted noise signal is subtracted from those subsequent measurement signals to provide corrected measurement signals.