oa Environmental applications of airborne geophysics in Finland

Geological Survey of Finland (GSF) has carried out systematic airborne geophysical surveys in Finland since 1951. The second program started in 1972 using a flight altitude of 30-40 meters and line spacing of 200(100) meters (Kurimo, et al, 1986; Peltoniemi, 1982; Poikonen, 1991; Vironmäki, et al, 1982). Today 80 % of the country has been measured. The measurements have been made with fixed-wing aircraft The differential GPS is utilised in navigation. In low-altitude measurements the following systems are in use: magnetic, gamma radiation and vertical coplanar EM and VLF eleciromagnetic. Total magnetic field is measured with a wingtip gradiometer. The horizontal spacing between the sensors is 21 meters. Earth's gamma radiation is measured with a spectrometer which utilises a 25 1 NAI crystal detector. In the electromagnetic unit a vertical coplanar coil configuration is used. The frequency is 3112Hz (from 1995 also 14368 Hz) and coil separation is 21.4 m. GSF processes data with in-house software and profile, contour, shaded colour and grey scale maps are drawn (Kurimo, et al. 1986). The survey results are used in mineral exploration and geological mapping, recently also increasingly in environmental applications.