Aeromagnetics and gravity

Residual Magnetic Field: This image shows the colour-coded map of the residual magnetic field. The image has a pixel size of 200m which results from gridding of the digititally acquired flight-line survey data. The two main aeromagnetic surveys covering this area were flown between 1975 and 1978. A flight-line spacing of 800 m and flight altitude of 305 m above ground was used in both cases. A later, smaller survey linking the Ungava peninsula and Baffin Island was flown in 1996. 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 200m which results from gridding of the digititally acquired flight-line survey data. The two main aeromagnetic surveys covering this area were flown between 1975 and 1978. A flight-line spacing of 800 m and flight altitude of 305 m above ground was used in both cases. A later, smaller survey linking the Ungava peninsula and Baffin Island was flown in 1996. The International Geomagnetic Reference Field for the date and altitude of each survey has been removed. 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 mGalom-1 and a crustal density of 2 670 kgom-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 125-metre interval.