Publication Date:
2020-09-09
Description:
There is a cleardemand to increase detection depths in the context of raw materialexploration programs. Semi-airborne electromagnetic (semi-AEM) methodscan adress these demands by combining the advantages of powerful transmitters deployed on the ground with efficienthelicopter-borne mapping of the magnetic field response in the air.The penetration depth can exceed those of classical airborne EM systems,since low frequencies and large transmitter-receiver offsets can berealized in practice. Anovel system has been developed that combines high-moment horizontalelectric bipoletransmitters on the ground with low-noise three-axis induction coilmagnetometers, a three-axis fluxgate magnetometer and a laser gyroinertial measurement unit integrated within a helicopter-towed airborneplatform. The attitude data are used to correct the time series formotional noise and subsequently to rotate into an Earth-fixed referenceframe. In a second processing step, and as opposed to existing semi-airbornesystems, we transform the data into the frequency domain and estimatethe complex-valued transfer functions between the received magneticfield components and the synchronously recorded injection currentby regression analysis. This approach is similar to the procedureemployed in controlled-source EM. For typical source bipole momentsof 20-40 kAm and for rectangular current waveforms witha fundamental frequency of about 10 Hz, we can estimate reliable three-componenttransfer functions in the frequency range from 10-5000 Hzover a measurement area of 4 x 5 km2 for a singlesource installation. The system has the potential to be used for focusedexploration of deep targets.
Print ISSN:
0016-8033
Electronic ISSN:
1942-2156
Topics:
Geosciences
,
Physics
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