S U M M A R YThe CHAMP magnetic field mission is providing highly reliable measurements from which the global lithospheric magnetic field can be determined in unprecedented resolution and accuracy. Using almost 5 yr of data, we derive our fourth generation lithospheric field model termed MF4, which is expanded to spherical harmonic degree and order 90. After subtracting from the full magnetic field observations predicted fields from an internal field model up to degree 15, an external field model up to degree two, and the predicted magnetic field signatures for the eight dominant ocean tidal constituents, we fit and remove remaining external fields and polar electrojet signatures in a track-by-track scheme. From a subset of least disturbed tracks, we estimate the MF4 model by least squares, damping ill-determined coefficients by regularization. The resulting MF4 model provides a good representation of the lithospheric field down to an altitude of about 50 km at lower latitudes, with reduced accuracy in the polar regions. Crustal features come out significantly sharper than in previous models. In particular, bands of magnetic anomalies along subduction zones become visible by satellite for the first time.

[1] Marine and airborne magnetic anomaly data have been collected for more than half a century, providing global coverage of the Earth. Furthermore, the German CHAMP satellite is providing increasingly accurate information on large-scale magnetic anomalies. The World Digital Magnetic Anomaly Map project is an international effort to integrate all available near-surface and satellite magnetic anomaly data into a global map database. Teams of researchers were invited to produce candidate maps using a common pool of data sets. Here we present the National Geophysical Data Center (NGDC) candidate. To produce a homogeneous map, the near-surface data were first line-leveled and then merged by Least Squares Collocation. Long wavelengths were found to agree surprisingly well with independent satellite information. This validates our final processing step of merging the short-wavelength part of the nearsurface data with long-wavelength satellite magnetic anomalies.Components: 5515 words, 5 figures, 1 table.

[1] Reliable global crustal field anomaly maps produced from magnetic measurements of the CHAMP satellite mission now allow for quantitative geological studies of crustal structure and composition. We have developed a GIS based forward modeling technique to model these anomaly maps. On the basis of the geologic and tectonic maps of the world, laboratory susceptibility values of the occurring rock types, and the seismic thickness of the crust, a vertically integrated susceptibility grid is generated in the GIS system. In addition, a remanent magnetization grid is computed for the oceanic crust using a digital isochron map of the ocean floor and rotation models of the paleoplates. Combining the global VIS and remanent magnetization grids, the vertical magnetic field anomaly is computed at satellite altitude and compared with the corresponding CHAMP magnetic anomaly map. Over the oceans, induced and remanent magnetization explains well the prominent observed anomalies over the Cretaceous quiet zones. We also find a good agreement between predicted and observed anomalies over the continents. Remaining discrepancies between the predicted and observed anomalies can be used to adjust poorly known boundaries and the composition of the buried Precambrian provinces, until the recomputed anomalies fit the observed anomalies. The feasibility of this approach is demonstrated on Greenland, the West African Craton, Bangui in central Africa, and the Kolyma-Omolon Block in Siberia. We conclude that quantitative information on the lateral extent, the composition and the thickness of the lower crust within a Precambrian province can thus be inferred from the new satellite magnetic anomaly maps.Citation: Hemant, K., and S. , Geological modeling of the new CHAMP magnetic anomaly maps using a geographical information system technique,

[1] Six years of low-orbit CHAMP satellite magnetic measurements have provided an exceptionally highquality data resource for lithospheric magnetic field modeling and interpretation. Here we describe the fifth-generation satellite-only magnetic field model MF5. The model extends to spherical harmonic degree 100. As a result of careful data selection, extensive corrections, filtering, and line leveling, the model has low noise levels, even if evaluated at the Earth's surface. The model is particularly suited for inferring large-scale structure and composition of the lithosphere. It is also meant to serve as the long-wavelength part of continental-and global-scale marine and aeromagnetic anomaly maps.

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