HIGH RESOLUTION MAGNETIC GRADIOMETER SURVEYS
(FIXED-WING OR HELICOPTER)

Sander Geophysics offers low level magnetic gradiometer surveys of very high resolution and accuracy.  The gradiometers use two cesium magnetometers with a fixed separation to measure the earth's vertical and/or horizontal magnetic gradient.   Total magnetic field measurements are recorded simultaneously.

The vertical magnetic gradient offers a better means of detecting near surface magnetic sources than total magnetic field measurements, making the gradient method ideal for mineral prospecting.  Gradiometer surveying can obtain exceptionally detailed data by flying at low altitudes and moderate speeds.

Horizontal gradients provide detailed near-surface information, and help to interpolate between survey flight lines.  This is especially important if the survey target has similar dimensions to the survey line spacing.  Both gradients are much less affected by diurnal changes in the magnetic field so they are ideal for use in areas where significant diurnal activity are expected.

We use optically-pumped cesium magnetometers with a sensitivity of 0.005 nT, and real-time digital compensation, giving an overall system resolution of 0.01 nT.  The magnetometers in the aircraft and in the ground station are identical, ensuring that all magnetometer data sets are equivalent in terms of sensitivity and noise envelope.  The sampling rate can be adjusted from 2 to 10 Hz depending on survey specifications.

Cesium magnetometers are ideally suited for gradiometer surveying because of their very high resolution and exceptional stability.  Flight direction changes do not require reorientation of the magnetometer sensors.

 

Good navigation and accurate flight path recovery are very important considerations for high resolution airborne gradiometer surveying.  Our aircraft are equipped with Global Positioning System (GPS) integrated into a proprietary navigation and flight path recovery system.  This system, called SGNav, allows for excellent navigation providing an accuracy of better than 1 m in post-flight recovery.

Sander Geophysics is well equipped to provide data processing, a variety of map presentations and interpretation services to enhance the usefulness of its vertical gradient surveys.
AIRBORNE INSTRUMENTS
Magnetometer Sensor Geometrics
Strap-down, optically pumped, cesium split beam
Sensitivity:  0.005 nT
Sensor noise level:  < 0.02 nT
Sampling rate:  10 Hz
Sensor Separation Helicopter:  3.0 m vertical
Fixed-wing:  2.64 m vertical and 19 m horizontal
Gradient Noise Level Less than 0.02 nT/m vertical   
Less than 0.005 nT/m horizontal
Compensator Sander Geophysics - AIRComp real-time digital compensation
Range:  20,000 to 100,000 nT
Resolution:  0.001 nT
Sampling rate:  10 Hz
Data Acquisition System Sander Geophysics - SGDAS airborne computer.
Capable of recording unlimited number of channels at variable intervals, and digital scrolling chart display of the data.  Data is recorded on a vibration tolerant removable drive.  The system clock is a quartz time standard automatically synchronizsed to UTC by the GPS signal to an accuracy of 1 millisecond.
Video Imaging System Sander Geophysics - SGDIS digital video
  Resolution Calibrated to Range
Radar Altimeter TRT AHV8 0.5 m 1% 0 to 3,050 m  (10,000 ft)
King KRA-10 0.1 m 1% 0 to 760 m  (2,500 ft)
Freeflight 0.5 m 1% 0 to 760 m  (2,500 ft)
Barometric Altimeter Sander Geophysics Digitally Recording Barometric Altimeter 2 m +/-4 m 0 to 10,000 m  (30,000 ft)
GROUND STATION INSTRUMENTS
Magnetometer Sensor Same as airborne
Magnetometer Interface Sander Geophysics - SGRef
Range:  20,000 to 100,000 nT
Resolution:  0.01 nT
Sampling rate:  2 Hz
Data Acquisition System Sander Geophysics - SGRef
THis system runs SGL data acquisition software capable of recording unlimited number of channels at variable intervals, and digital scrolling chart display of the data.  Data is recorded on a vibration tolerant removable drive.  The system clock is a quartz time standard automatically synchronised to UTC by the GPS signal to an accuracy of 1 millisecond.
Power Source 12 VDC can be wind or solar powered
NAVIGATION INSTRUMENTS
Global Positioning System NovAtel - 12-channel, dual frequency GPS receiver, (ground & airborne)
Sampling rate:  1 to 10 Hz
Real-Time Differential GPS Satellite link (OmniStar or LandSTAR) to the aircraft for real-time in-flight differential GPS (RDGPS)

 

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