With over 500,000 lkm’s of gravity survey completed, the system delivers by combining industry-leading Gravimetric Technology gravimeters mounted using NRG patented technology in a Pilatus PC6 aircraft renowned for its ability to fly slowly.



With over 500,000 Ikms of gravity survey completed, the Xtract™ system delivers by combining industry-leading GT gravimeters with an ideal slow-flying aircraft platform.

At the heart of the patented Xtract™ gravity system is a GT2A total field gravimeter. Initially designed and built by Joint Stock Company Gravimetric Technologies in the Russian Federation. The system has been employed in both military and civilian applications and includes extensive use in airborne geophysics as an airborne gravimeter.

The standard GT2A does however suffer from short-term, temperature related drift. This is not ideal when mapping large long-wavelength sedimentary basins.

NRG™ has developed the Xtract™ system which incorporates a patented thermal control system for the unit. This reduces the random drift present in standard GT2A systems significantly. The residual drift in the patented Xtract™ system is greatly reduced and linear.  This results in previously unobtainable crossover results, which translates to exceptional accuracy and repeatability of the final product.


Standard GT2A meter

NRG’s patented Xtract™ thematically controlled unit


The graph below shows the difference between the pre and post flight readings for seven flights with the patented Xtract ™ thermal control system and seven flights with a standard GT2A gravimeter. The drift in all instances was determined by taking readings at the same base position on the ground before and after production survey flights. The drift envelope of the Xtract™ system is about 0.2 mGals whilst the drift envelope of the standard GT2A is significantly larger by a factor of three, at 0.6 mGals.




The gravity sensor, mounted inside the Xtract ™ system, is a custom-designed accelerometer mounted inside a gyro-stabilised unit. Inputs from the gyros, inclinometers, angle sensors and dual frequency GPS are used to drive servo motors which maintain the sensor in a vertical position. The entire assembly is mounted on a rotation table, maintaining the sensor orientation at the same heading.


Gravimetric Technologies GT meter at the core


As per all airborne gravimeters, the raw data is filtered with time based and user selectable filters. As a result, the resolution of gravity data is directly proportional to survey speed. The Pilatus PC6 is renowned for its STOL capability and exceptionally low stall speed, resulting in the highest possible resolution of data.

In addition to the Pilatus’s slow cruising speed, the aircraft has an exceptional endurance with long-range tanks and is ideally suited for the large prospect areas typically covered in airborne gravity surveys. The Porter is fully capable of operating from different types of unprepared, rough and short airstrips, in remote areas, at high altitudes and in all climates. A simple but solid construction, proven systems and features, combined with precision workmanship result in the highest reliability and lowest field maintenance possible.


Key features of the system include:

  • Xtract™ patented thermal control system
  • Low and linear drift rates, resulting in improved accuracy and repeatability
  • Highest possible resolution ensured by a low flight speed
  • High precision 3-axis Schuler-tuned platforms with vertically constrained sensing element limits contamination from horizontal accelerations
  • High productivity and less susceptibility to turbulence – minimised horizontal coupling and accurate vertical velocity mapping allows for production in a larger turbulence window
  • Safe operations from remote flight bases
  • Minimal in field maintenance required
  • Consistent high quality, accurate and repeatable data


The Pilatus PC-6 aircraft is owned by NRG™ and is a dedicated full-time survey platform. It has therefore been subject to an intense magnetic clean up and degaussing process.  This ensures the collection of very low noise magnetic data. The magnetic sensor configuration in the Xtract™ system is a Caesium cell, fixed boom installation.

This magnetic data is compensated using our specially adapted and modified 27-term compensation algorithm. The raw data is collected as a base frequency of 1000 Hz enabling intelligent removal of external interference such as radar, radio transmissions and culture.

The resultant 20 Hz final processed data is extremely clean, resulting in the highest possible standard of magnetic grids and enhanced products.



Magnetic Platform
TypeTotal Field
Typical noise envelope0.001nT/m SDEV 4th diff
Aircraft TypePilatus PC6 (“Porter”)
Engine TypeTurbine PT6-27
Fuel TypeJetA1
Acquisition System
CPUPentium 4 800Mhz
Operation Temperature-10 to 65 Degrees C
Standard Sampling Rate20 Hz
Magnetometer Counter
Counter Frequency1000Hz
Internal System Noise<0.0001 nT
Adc Inputs10
Magnetometer Inputs8
Recording Rate20 Hz
Magnetometer Sensor
TypeScintrex CS3
Measurement Range15 000 – 105 000 nT
Noise Envelope0.002 nT
Gradient Tolerance40 000 nT/m
Operating Temperature-40 to +50 Degrees C
Recording Rate20 Hz
Sensitivity0.0006nT Hz RMS
Fluxgate Magnetometer
Analogue output+- 10 V
Linearity error<0.0015%
Calibration accuracy-0.005
Bandwidth0.3 KHz
Internal noise<6 pTrms/Hz @1Hz
Recording rate20 Hz
Base Station Magnetometer
ManufacturerNRG Engineering
Range15 000 to 105 000nT
Sensitivity0.0006nT Hz RMS
Recording Rate1Hz
GPS Base Station
TypeNovatel DL-V3 OEMV L1,L2
Code TrackedL1 C/A, L2 P(Y), L1 Carrier Phase, L2 Carrier Phase
Recording Rate2Hz
No. of Satellites12
Gravity Meter
TriggerExternal GPS
Recording Rate2 Hz
Measurement Range± 0.25 g, ± 0.5 g and ±1.0 g
Sample Rate20 Hz
Pressure Resolution0.001 mb
Operating Pressure Range600 – 1060 mb
Recording Rate20 Hz
Sample Rate20Hz
Resolution0.05 DegC
Accuracy0.1 DegC
Recording Rate20 Hz
Radar Altimeter
TypeFree Flight
Operating range0 – 762 m
Accuracy 0 – 10 m±0.3m
Accuracy 10 – 762 m±0.5%
Recording rate20 Hz
GPS Navigation
TypeNovatel DL-V3 OEMV L1,L2
Differential CorrectionReal Time
Code TrackedL1 C/A, L2 P(y)
Number of Satellites12
Recording Rate10 Hz Triggered
Processing Software PlatformsGeosoft Oasis Montaj, Waypoint GrafNav,GTGRAV and GTNAV, Propriety Software

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