GLOBAL MAGSAT ANOMALY MAPS AT GROUND-LEVEL

Four maps of the vertical component of the magnetic anomaly field are derived at ground level from Magsat data at satellite altitude. Measur ements performed below and above an altitude of 425 km are treated as two independent datasets by two different methods: (1) a local downwar d continuation inverse method and (2) a global spherical harmonic deco mposition. For each map, one-and two-dimensional energy density spectr a are obtained and correlation coefficients are computed. It is shown that anomalies with wavelengths as short as 700 km can be significantl y recovered at ground level, corresponding to a ground resolution of 3 50 km. The improved correlation between anomalies and geodynamic featu res achieved with downward-continued maps is illustrated with the exam ple of Southeast Asia.