Aeromagnetic and gravity

Abstract

Residual magnetic field: This image shows the colour-coded map of the residual magnetic field. The image has a pixel size of 42m. The area north of 65N consists of digitized data resulting from two surveys flown between 1966 and 1974. A flight-line spacing of 800 m and flight altitude of 305 m above ground were used in both cases. South of 65N, data were acquired digitally in three surveys flown between 1996 and 1997. A flight-line spacing of 800 m and flight altitude of 150 m above ground were used for these surveys. The International Geomagnetic Reference Field for the date and altitude of each survey has been removed. Vertical gradient of residual magnetic field: This image shows the colour-coded map of the vertical gradient of the residual magnetic field. The image has a pixel size of 42m. The area north of 65N consists of digitized data resulting from two surveys flown between 1966 and 1974. A flight-line spacing of 800 m and flight altitude of 305 m above ground were used in both cases. South of 65N, data were acquired digitally in three surveys flown between 1996 and 1997. A flight-line spacing of 800 m and flight altitude of 150 m above ground were used for these surveys. Calculation of the vertical gradient of the residual magnetic field emphasizes the magnetic effects of near surface magnetic sources and suppresses the effects more deep-seated sources. Therefore, it is an effective way of highlighting those anomalies related to surface geological variations (lithological and structural). Compared to the residual magnetic field image, the vertical gradient image is more detailed - it contains more short-wavelength information. Bouguer gravity anomalies: This image shows the colour-coded map of the Bouguer gravity anomalies. The gravity data used to compile this map have a spacing of 10 km, on average. All measurements were reduced to the IGSN71 datum and theoretical gravity values were calculated from the Geodetic Reference System 1967 (GRS67) gravity formula. Bouguer anomalies were calculated using a vertical gravity gradient of 0.3086 mGal·m-1 and a crustal density of 2 670 kg·m-3. Areas on land are represented by Bouguer anomalies and areas offshore, by free-air anomalies. For this map, the data were gridded to a 2 km interval. The image grid has a 127-metre interval.