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Abstract

The Federal Institute for Geosciences and Natural Resources of Germany (BGR) completed a<br>research and development project aiming at optimising its helicopter-borne geophysical system for<br>circumstances relevant for high resolution site characterisation. The overall objective was to adapt the<br>existing helicopter-borne geophysical system previously used for groundwater and mineral exploration<br>to survey conditions where the anomalies to be recorded are much smaller in shape and size.<br>The BGR helicopter-borne system permits simultaneous electromagnetic (AEM), magnetic, and<br>natural gamma-ray surveying. At the suggestion of the BGR, the AEM system manufactured by<br>Geoterrex-Dighem, Toronto, includes several improvements<br> increased dipole moment<br> only horizontal coplanar coils<br> minimum interference by overlapping coils<br> operation at five frequencies<br> new calibration concept: amplitude and phase calibration during flight.<br>These instrumental modifications were tested running various surveys over two former military<br>training areas south of Berlin, Germany. Special detection surveys to locate typical waste, such as<br>individual steel drums, scrap metal, steel pipes, petrol tanks, ordnance, buried at depths varying from<br>0.3 – 1.5 m were carried out with a nominal flight line spacing of 50 m. AEM and magnetic anomalies<br>produced by these materials are extremely weak and in the order of only 1 ppm or 0.1 nT at a height of<br>app. 25 m a.g.l. Therefore, suitable detection algorithms were developed and tested using an airborne<br>data set collected over an area where thousands of individual anomalies were identified. Lots of them<br>were subsequently verified on the ground. More than 95% of the anomalies selected for verification<br>could be confirmed either by visual inspection of the ground surface or ground geophysical surveying or<br>excavation. The GPS/GLONASS positioning error was less than 10 m in most cases.

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/content/papers/10.3997/2214-4609-pdb.192.LWS_5
2001-03-04
2020-04-02
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