Helicopter-borne magnetic, electromagnetic and radiometric geophysical survey in the Alta - Kvænangen area, Troms and Finnmark

Abstract

NGU conducted an airborne geophysical survey in Kvænangen area in September-October 2012. This report describes and documents the acquisition, processing and visualization of recorded datasets. The geophysical survey results reported herein are 5526 line km.The Geotech Ltd. Hummingbird frequency domain system supplemented by optically pumped ceasium magnetometer and 1024 channels RSX-5 spectrometer was used for data acquisition. The survey was flown with 200 m line spacing, line direction 90\u00B0 W-E in the western part of the area and 125\u00B0 in the eastern part with the average speed 93 km\/h. The average terrain clearance of the EM bird was 58 m.Collected data were processed at NGU using Geosoft Oasis Montaj software. Raw total magnetic field data were corrected for diurnal variation and levelled using standard microlevelling 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 levelled and filtered. Radiometric data were processed using standard procedures recommended by International Atomic Energy Association.All data were gridded with the cellsizeof 50 m and presented as a map at the scale of 1:50 000.