Helicopter-borne magnetic, electromagnetic and radiometric geophysical survey in Rombaken area, Narvik, Nordland
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- Rapporter 
NGU conducted an airborne geophysical survey in Rombaken area in August - September 2011 as a part of MINN project. This report describes and documents the acquisition, processing and visualization of recorded datasets. The geophysical survey results reported herein are 5218 line km. The modified Geotech Ltd. Hummingbird frequency domain system supplemented by optically pumped cesium magnetometer and 1024 channels RSX-5 spectrometer was used for data acquisition. The survey was flown with 200 m line spacing, line direction of 90\u00B0 East West and average speed 98 km\/h. The average terrain clearance of the bird was 64 m. Collected data were processed in NGU using Geosoft Oasis Montaj software. Raw total magnetic field data were corrected for diurnal variation and levelled using standard micro levelling algorithm. EM data were filtered and levelled using both automated and manual levelling procedure. Apparent resistivity was calculated from in-phase and quadrature data for each of the five frequencies separately using a homogeneous half space model. Apparent resistivity dataset was filtered and levelled. Radiometric data were processed using standard procedures recommended by International Atomic Energy Association. All data were gridded with the cell size of 50 m and presented as a shaded relief maps at the scale of 1:50 000.