TEMPEST AEM FORM 2000
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1. The document discusses airborne electromagnetic (AEM) surveys using the TEMPEST system. It describes the basic principles of AEM including how the conductivity distribution below ground affects the response measured. 2. It provides details on the development of the TEMPEST system through the Cooperative Research Centre for Australian Mineral Exploration Technologies (CRC AMET) involving several research organizations. 3. The TEMPEST system collects digital elevation data, magnetic data, and airborne EM response data which are then processed to generate conductivity models and maps revealing details about subsurface geology and groundwater resources.
TEMPEST AEM FORM 2000
- 1. 1 Fugro Airborne SurveysFugro Airborne Surveys TEMPESTTEMPEST Airborne EM SystemAirborne EM System AEM FundamentalsAEM Fundamentals • Ground response is a function of the conductivity distribution. • The goal of AEM systems is to derive a 3D representation of the sub-surface conductivity distribution as an input to interpretation processes. TransmitterTransmitter ReceiverReceiver GroundGround “primary field” “secondary (ground) response” “induction”
- 2. 2 TEMPEST installed on Trislander aircraftTEMPEST installed on Trislander aircraft Development GroupDevelopment Group Cooperative Research Centre for Australian Mineral Exploration Technologies (CRC AMET) • Australian Geological Survey Organisation (AGSO) • Commonwealth Scientific and Industrial Research Organisation (CSIRO) • Curtin University • Macquarie University • World Geoscience Corporation (now Fugro Airborne Surveys)
- 3. 3 CRC AMET ProgramsCRC AMET Programs • Software Development • Forward modelling • Approximate transformation • Hardware • Interpretation • Education Development TimelineDevelopment Timeline • 1960’s INPUT • Late 1980’s GEOTEM and QUESTEM (digital INPUT) • 1992 CRC AMET commences • 1998 TEMPEST prototype • 1999 TEMPEST commercialised • 2000 Australian Fedral Government recognises the “ultra-sound of the Earth” • 2000 CRC AMET concludes • 2001 TEMPEST installed on 3rd aircraft • 2001 TEMPEST prepared for international deployment
- 4. 4 TEMPEST ProductsTEMPEST Products Digital elevation model Magnetics Airborne EM response Conductivity Digital Elevation ModelDigital Elevation Model Aircraft path Ground surface Ellipsoid Sea-level Satellite positioning Radar and/or laser altimeter Geodetic surveys Height above sea-level
- 5. 5 MagneticsMagnetics • Earth’s magnetic field • Induced magnetisation • Remanent magnetisation • Mapping the distribution of magnetite (+/- pyrrhotite) over a very large range of concentrations from 0.01% to 100% Airborne EM ConfigurationAirborne EM Configuration Transmitter loop Receiver coils Surface
- 6. 6 Transmitter Loop FieldTransmitter Loop Field Secondary Currents in the GroundSecondary Currents in the Ground
- 7. 7 Field of Secondary Currents (Conductive)Field of Secondary Currents (Conductive) Field of Secondary Currents (Resistive)Field of Secondary Currents (Resistive)
- 8. 8 Airborne EMAirborne EM -- Multiple FrequenciesMultiple Frequencies Depth High Frequency Middle Frequency Low Frequency ( TEMPEST (25 Hz) uses 750 frequency terms for conductivity and depth discrimination ) Response Contribution Advances made with TEMPESTAdvances made with TEMPEST • Spatial sampling • Signal to noise • hardware • processing • Bandwidth • Calibration • system response • geometry • amplitude • timing/phase • Emphasising conductivity transformation
- 9. 9 Conductivity TransformationConductivity Transformation • Optimum for integration and follow-up. • Overcome complexity of measured response (system characteristics, variations in geometry of Tx-Rx-ground). • Ideally, the final output of an airborne EM survey would be a 3-D conductivity distribution. • 1-D conductivity transformations are the only practical methods at present. • Conductivity is the primary form of output for some applications (e.g. regolith mapping, mapping for salinity, groundwater) but a secondary form for discrete conductor applications. Conductivity TransformationConductivity Transformation Measured (or even processed) response is a complex function of system characteristics and variations in the geometry of the transmitter loop, receiver coils and ground asinh(B-field)(fT) 0 1 2 3 0 4 km1 2 3
- 10. 10 Conductivity TransformationConductivity Transformation 0 4 km1 2 3 240 340 m ASL 100 1000 mS/m 0 1 2 3 asinh(B-field)(fT) Conductivity sections are much more intuitive to interpret and are much easier to integrate with other information such as boreholes Factors Affecting ConductivityFactors Affecting Conductivity • Conductive lithologies (eg sulphides, graphite) and / or • Fluid • porosity • saturation • permeability • salinity • presence of other salts • clay content • formation factor • temperature
- 11. 11 Project PhasesProject Phases • Defining the purpose and initial planning • Initial data gathering • including measurement of geo-electric properties and establishing a link between conductivity and groundwater • Revised planning • Acquisition and processing • Validation • Analysis and interpretation • Recommendations • Ground follow-up