Equipment
A typical Geotech airborne geophysical system comprises the following main instrumentation:
A time-domain electromagnetic system (VTEM)
A high-sensitivity cesium magnetometer
A radar altimeter
A GPS navigation system
A cesium magnetometer base station
1. VTEM System
Geotech's helicopter-borne time domain electromagnetic system (VTEM) is the new technology device effectively using modern advantages of digital electronics and signal processing, and recent company research results in the area of precision electromagnetic measurements.
1.1 The system was designed as a very low noise system. The minimized noise level is as effective as the dramatically increased transmitter dipole moment. The excellent signal to noise ratio determines the superb abilities of the system as:
Deep penetration;
High spatial resolution;
Best resistivity discrimination;
Detection of weak anomalies.
1.2 The system was designed to be flexibly adjustable to different geophysical requirements such as priority of deep penetration or optimal for different resistivity ranges.
1.3 The system is very transportable. It can be disassembled for packaging in relatively small units for shipping to distant survey areas.
1.4 The system has an excellent surviving ability. The unique design of the system allows an easy replacement of any part of the system in the field, in case the EM bird gets damaged.
The resent surveys flown with the Geotech system have picked up a number of anomalies left undetected by the previous airborne EM surveys. The Geotech TDEM system flew the Reid-Mahaffy, Caber, Perserverance and Montcalm test ranges. The results of the tests have demonstrated that Geotech TDEM system provides the industries highest signal/noise ratio and the conductor spatial resolution. The receiver and transmitter coils are concentric and Z-direction oriented. The transmitter loop can be assembled or disassembled in 3-4 hours.
2. Magnetometer
A Geometrics/Scintrex split-beam total field magnetic sensor, with a sampling interval of 0.1 seconds and an in-flight sensitivity of 0.02 nT, is utilized. The magnetometer will perform continuously in areas of high magnetic gradient with the ambient range of the sensor approximately 20k-100k nt.
3. Electronic Navigation - GPS
A Geotech GPS navigation system utilizing the NovAtel's WAAS enable OEM4-G2-3151W GPS receiver provides in-flight navigation control. This system determines the absolute position of the helicopter in three dimensions by monitoring the ranges to orbiting satellites. As many as 11 GPS and two WAAS satellites may be monitored at any one time. The position accuracy (CEP) is 1.8 m, with WAAS on - 1.2 m.
4. Altimeter
An altimeter system records the ground clearance to an accuracy of about 1 m.
5. Data Acquisition/Recording System
A Geotech data acquisition system is used. Data is recorded on a PCMCIA flash card.
6. Field Computer Workstation
A dedicated PC-based field computer workstation is used in the field for purposes of displaying geophysical data for quality control, calculating and displaying the navigation, producing preliminary EM anomaly information and magnetic maps, and copying/verifying the digital data.
7. Base station
A dedicated computer including high sensitivity base station cesium magnetometer is employed to record magnetic activity.
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