Orsted and Magsat scalar anomaly fields

The scalar anomaly field determined from available Orsted data is compared with the upward continued scalar anomaly field derived from Magsat data. Tw o techniques were used to remove the core field from the Orsted satellite d ata. In the first method, monthly spherical harmonic core field models of d egree and order 13 derived from scalar and vector data were subtracted, and in the second method, along-track high-pass filtering of scalar data only was used. In both methods, the binned residuals were interpolated to a sphe re, and subsequently filtered. Monthly degree and order 13 spherical harmon ic core field models were removed from Magsat vector data. The binned Magsa t vector residuals were interpolated to a sphere, filtered, and upward cont inued by high degree spherical harmonic analysis. The corresponding Magsat scalar anomaly field at Orsted altitude was then determined. For latitudes below 50 degrees, removal of the core field by signal processing techniques from presently available Orsted data led to a scalar anomaly field in bett er agreement with that determined from Magsat data, than removal by spheric al harmonic analysis.