Summary
NGU conducted an airborne geophysical survey in Mjøsa, Innlandet county as part of
NGU’s general airborne mapping program in 2020.
This report describes and documents the acquisition, processing and visualization of the
acquired datasets and presents them in maps. The geophysical surveys consist of 2146 linekm data, covering an area of 458 km2 flown on August 30th to September 07th, 2020.
The NGU modified Geotech Ltd. Hummingbird frequency domain EM system supplemented
by an optically pumped Cesium magnetometer and the Radiation Solutions 1024 channels
RSX-5 spectrometer mounted on a AS350-B3 helicopter was used for data acquisition.
The survey was flown with 200 meters line spacing, azimuth 90o
. Average speed was
135 km/h, and average height clearance of the EM bird was 50 m and 80 m for the
spectrometer.
Collected data were processed at NGU using Geosoft Oasis Montaj software. Raw total
magnetic field data were corrected for diurnal variation and leveled using standard micro
levelling algorithm. Radiometric data were processed using standard procedures
recommended by International Atomic Energy Association (IAEA).
EM data were filtered and leveled using both automated and manual levelling procedures.
Apparent resistivity was calculated from in-phase and quadrature data for three coplanar
frequencies (880 Hz, 6.6 kHz and 34 kHz), and for two coaxial frequencies (980 Hz and 7 kHz)
separately using a homogeneous half space model of 500 ohm-m.
All data were gridded using cell size of 50x50 meters. Magnetic and radiometric data is
presented as 40% transparent grids with shaded relief on top of topographic maps. EM data is
presented as 30% transparent grids on top of topographic maps.
