Comparisons of magnetic anomalies of lithospheric origin measured by satellite and airborne magnetometers over western Canada

Abstract

Crustal magnetic anomaly data from the Orbiting Geophysical Observatories 2,4, and 6 (Pogo) satellites are compared with upward-continued aeromagnetic data between 59-85"N latitude and 220-260"E longitude. Agreement is good, both in anomaly location and in amplitude, giving confidence that it is possible to proceed with the derivation and interpretation of satellite anomaly maps in all parts of the globe. The data contain a magnetic high over the Alpha ridge suggesting continental composition and a magnetic low over the southern Canada basin and northern Canadian Arctic Islands (Sverdrup basin). The low in the Sverdrup basin corresponds to a region of high heat flow, suggesting a shallow Curie isotherm. A ridge of high field, with two distinct peaks in amplitude, is found over the northern portion of the platform deposits and a relative high is located in the central portion of the Churchill Province. No features are present to indicate a magnetic boundary between Slave and Bear Provinces, but a trend change is evident between Slave and Churchill Provinces. South of 60" latitude a broad magnetic low is located over very thick (40-50 km) crust, interpreted to be a region of low magnetization.On compare les donnees recueillies par les satellites OGO 2, 4 et 6 (Pogo) sur les anomalies magnetiques dans la crofite avec un prolongement vers le haut des donnees atromagnetiques situees entre les latitudes 50-85"N et les longitudes 220-26O0E. L'accord est bon a lafois pour la localisation des anomalies et leur amplitude, ce qui permet d'itre optimiste quant a la possibilite de proceder a la confection et a I'interpretation de cartes d'anomalies magnetiques par satellite dans toutes les parties du globe. Les donnees contiennent un pic magnetique sur la crkte Alpha suggerant une composition continentale et une depression magnetique sur le bassin du sud du Canadaet dans les iles de 1'Arctique canadien au nord (le bassin de Sverdrup). Ladepression dans le bassin de Sverdrup correspond a une region de flux thermique eleve ce qui laisse supposer une isotherme de Curie afaible profondeur. Une crite de champ intense avec deux pics distincts dans I'amplitude se retrouve dans la partie nord des depBts de plate-forme et un sommet relatif est localise dans la portion centrale de la province de Churchill. I1 n'y a rien qui indique une limite magnetique entre les provinces de 1'Esclave et de I'Ours, il y a un changement evident entre les provinces de Churchill et de I'Esclave. Au sud de la latitude 60°N, on observe une vaste depression magnetique situee sur une croDte tres epaisse (40-50 km) et qu'on interprkte comme une region de faible aimantation.

A study of local time and longitudinal variability of the amplitude of the equatorial electrojet observed in POGO satellite data

“…Working with the 225 satellite passes that meet the low noise and altitude criterion, we remove the main field using the model POGO (2/72), which includes spherical harmonics up to degree and order 13 for both the constant and the first time-derivative terms (Langel et al, 1980). We use a highpass Kaiser filter with a cutoff wavelength of 12,000 km on a pass-by-pass basis following Langel et al (1993).…”

Some new methods in geomagnetic field modeling applied to the 1960-1980 epoch.

“…Those of us who have been attempting to study crustal magnetic anomalies have been using a model of degree/order 13 (LANGEL et al, 1980a). This choice is confirmed by LANGEL and EsTES (1982) who derived the spatial power spectrum (LowEs, 1966(LowEs, , 1974, (4) for n=1 to 23 using Magsat data. The derived spectrum showed a clear break near n=14 which was interpreted to mean that the core field dominates for n<13 and the crustal field for n>15.…”

“…Satellite data are not immune to these limitations, although they are not as severe. LANGEL and ESTES (1982) showed that crustal anomaly fields dominate the Magsat data for wavelengths shorter than those corresponding to degree and order fifteen. This means that with present methods of modeling, we cannot determine the main field representation beyond degree and order 13 or 14, regardless of the quality of our data.…”

“…The latest published models which include these data are mainly of degree/order 12 (BARRACLOUGH et al, 1975;PEDDLE and FABIANO,1976;BARKER et al, 1981). Those of us who have been attempting to study crustal magnetic anomalies have been using a model of degree/order 13 (LANGEL et al, 1980a). This choice is confirmed by LANGEL and EsTES (1982) who derived the spatial power spectrum (LowEs, 1966(LowEs, , 1974, (4) for n=1 to 23 using Magsat data.…”

Compatibility of high-altitude aeromagnetic and satellite-altitude magnetic anomalies over Canada

“…Some of these attempts used both qualitative and quantitative comparisons of satellite data with upward-continued aeromagnetic data (Langel et al, 1980;von Frese et al, 1982: Won and Son, 1982: Schnetzler et al, 1985Arkani-Hamed and Hinze, 1990) or downwardcontinued satellite data (Arkani-Hamed et al, 1985). The results of many of these studies implied that the correlation between the aeromagnetic and satellite anomalies was generally poor, but there were also significant similarities between the two data sets.…”