Fixed Wing Horizontal Gradiometer
The measurement of the earth’s horizontal magnetic gradient is particularly useful for detecting near surface magnetic sources. Exceptionally good gradiometer data can be gathered by flying slowly at very low altitudes. This is an ideal tool for kimberlite exploration. Terraquest was the first survey contractor to operate a commercial horizontal gradient system in 1989.Case Study; On a survey of an Alberta kimberlite, using the Cessna 206 platform equipped with the Horizontal Gradiometer (HG) system, the colour plot below, shows:
- Horizontal Gradient Vectors that pinpoint the correct location of the kimberlite between the flight lines.
- The single sensor mag is used to measure the Total Magnetic Intensity (TMI) shown as the colour image erroneously shows the kimberlite centered on the flight path
- Three cesium vapour sensors, mounted on extensions from each wing tip and tail
- 0.005 nT sensitivity recording at 10 to 20 times per second
- +/- 0.02 nT fourth difference noise envelope
- AGIS and SDAS fully integrated data acquisition systems
- Real time corrected GPS
- Digital video flight path confirmation at 1/10 second with fiducial and GPS location registration over print.
- Radar and Barometric altimeter data recorded
- Same day printed profiles of user selected scales and lay out
- Next day infield colour contour plots
- Primary advantage is improving the gridding and contouring of data for enhanced resolution
- Measured Horizontal Gradient data is useful in identifying:
- The precise location of small anomalies between flight lines
- The precise location of contacts, dykes and faults
- “Magnetic axis” within many of the magnetic units.
- The indication of the dip of some magnetic units
- The discrimination between cultural and small geological sources such as Kimberlite.