6.2 Interpolated In-field Referencing

One solution to diurnal variations is to use a reference station on surface. In this way, the observed variations observed at surface can be applied to the Downhole Data which will experience similar variation. This is not always practical and requires a magnetically clean site with power supply nearby and some method of transmitting the data in real time from the temporary observatory. The other issue is establishing the baseline from which these variations are occurring in order to correct to the right background field values.

In a combined research project between Sperry Sun and the British Geological Survey, it was discovered that the diurnal and other time variant disturbances experienced by observatories, even a long way apart follow similar trends. The researchers compared observations made at a fixed observatory with derived observations interpolated from those taken at other observatories some distance away. The match was very encouraging and a new technique for diurnal correction was established called Interpolated In-Field Referencing or IIFR (not be confused with IFR discussed below). This technique is a patented method of correcting for time variant disturbances in the Earth’s magnetic field but is widely used under licence from the inventors. The readings observed at the nearby stations are effectively weighted by the proximity to the drill site and the time stamped combined corrections applied to the Downhole observations either in real time or retrospectively.