The Canadian Geomagnetic Reference Field 1995

Abstract

Several innovations have been introduced in the production of the Canadian Geomagnetic Reference Field (CGRF) for 1995. The secular variation and main field were modelled simultaneously using the recently developed method of main field differences. The degree of the temporal polynomial was varied depending on the spherical cap harmonic spatial degree. Modifications were made to allow the use of scalar, as well as vector, data in the analysis. Use was made of several data sets not used in previous versions of the CGRF, including Project Magnet data, POGS data, low-level scalar aeromagnetic data, and scalar marine data. A spherical cap harmonic model was produced for a spherical cap of 30° radius centred at 65°N, 85°W. The maximum spatial index of expansion was K=16, and the maximum temporal expansion was 7. The CGRF results in an error variance to the data over the modelling area that is 19% lower for the main field data and 55% lower for secular variation data than does the IGRF.