Method

An overall description of modern airborne gamma-ray spectrometry methods can be found in IAEA Technical Report 323 (Airborne Gamma-Ray Spectrometer Surveying), and in AGSO Record 1995/60 ( A Guide to the Technical Specifications for Airborne Gamma-Ray Surveys).

Fugro Airborne Surveys follows the principles outlined in these reports for calibration, data acquisition and processing and uses more advanced techniques for specific aspects. We have extensive experience in the control of airborne radon using either upward-looking detectors or low energy spectral information.

In-field processing and map production capability ensures compliance with the detailed and strict Fugro standards with respect to the calibration, acquisition and processing of airborne gamma-ray survey data and facilitates production of quick and accurate preliminary results.

Equipment

Fugro Airborne Surveys uses Exploranium GR-820 or Fugro PGAM-1000 gamma-ray spectrometers.

Both spectrometers feature:

• Automatic Gain Control, which does not require operator adjustment or maintaining the crystals at a constant temperature;
• Accurate pulse-pile-up rejection;
• Internal shock mounting of sodium-iodide crystal detectors. 

The Exploranium GR-820 is a self-stabilising, multi-channel (256 or 512) spectrometer that can be configured with up to 67.2 litres of sodium-iodide detector volume. It includes an upward-looking detector spectrometer which may be configured with up to 12.6 litres of detector volume. The GR-820 is a proven, rugged and reliable instrument. 

The PGAM-1000 256 channel self-calibrating gamma ray spectrometer was designed and manufactured by Fugro Airborne Surveys. It features the option to accumulate spectral information for up to 4 detectors individually (i.e., internal sampling of 1024 channels). This improves the overall resolution of the summed 256 channel spectra.

The GR-820 or PGAM-1000 is coupled to one of Fugro's state of the art acquisition systems on a fixed wing or helicopter platform and is guided by real time differential global positioning system (DGPS) navigation. Radar altimeter, barometric and temperature sensors are also employed on airborne gamma-ray spectrometer surveys. Radiometrics surveys can be flown in conjunction with other Fugro airborne instruments such as EM, VLF and/or magnetometer systems. The lift capabilities of the aircraft and the weight of other geophysical systems on the same aircraft may limit the detector volume in some cases.