The Second National Aerogeophysical Mapping Project

The Geological Survey of Finland (GTK) began systematic airborne geophysical mapping in 1951, being one of the first organizations in the world. The First National Airborne Geophysical Mapping Program of Finland, between 1951 and 1972 was based on magnetic (fluxgate) and electromagnetic methods. The whole country was mapped at flight altitude of 150 m using line spacing of 400 m.The Second National Aerogeophysical Mapping Program started in 1972 and ended 2007. This  program was based on multisensor equipment and extra high resolution digital aerodata: the flight altitude being 30 - 40 m and line spacing 200 m.One guide line of our national mapping project has been and still is, simultaneous measurement of as many geophysical parameters as possible. Thus, the equipment includes magnetic, electromagnetic and gamma-ray measurement systems. The present magnetic system consists of two cesium magnetometer sensors at the wing tips to allow measurement of the magnetic horizontal gradient across flight lines. This procedure improves the quality of maps showing better magnetic anomalies between flight lines thus tightening the flight line separation without extra costs. The present EM system includes 2 frequencies which gives 4 components for interpreting electrical properties of the ground on different depths. The modern spectrometer includes 2 crystal packages with downward and upward looking crystals.The in-house made data collection system gathers all geophysical and navigational measurements simultaneously improving the processing speed and capabilities immediately after the flights. GTK is still one of the few organisations that can measure simultaneously with magnetic, gamma-ray and active two-frequency electromagnetic system using fixed wing aircraft.The annual portion of this project comprises, for example, selection of the areas to be flown, detailed flight planning and optimization, preparation of flight maps and flight line information, planning and establishing the ground base station sites, arranging maintenance and fuel for the aircraft etc. In all these tasks the pilots, the operators, the data gatherers in the field, and the staff in the home office form an exceptionally powerful team with the experience and knowledge necessary to work in very "demanding" surroundings.