We derive a new model, named LCS-1, of Earth's lithospheric field based on four years (2006 September-2010 September) of magnetic observations taken by the CHAMP satellite at altitudes lower than 350 km, as well as almost three years (2014 April-2016 December) of measurements taken by the two lower Swarm satellites Alpha and Charlie. The model is determined entirely from magnetic 'gradient' data (approximated by finite differences): the north-south gradient is approximated by first differences of 15 s along-track data (for CHAMP and each of the two Swarm satellites), while the east-west gradient is approximated by the difference between observations taken by Swarm Alpha and Charlie. In total, we used 6.2 mio data points. The model is parametrized by 35 000 equivalent point sources located on an almost equal-area grid at a depth of 100 km below the surface (WGS84 ellipsoid). The amplitudes of these point sources are determined by minimizing the misfit to the magnetic satellite 'gradient' data together with the global average of |Br| at the ellipsoid surface (i.e. applying an L1 model regularization of Br). In a final step, we transform the point-source representation to a spherical harmonic expansion. The model shows very good agreement with previous satellite-derived lithospheric field models at low degree (degree correlation above 0.8 for degrees n ≤ 133). Comparison with independent near-surface aeromagnetic data from Australia yields good agreement (coherence > 0.55) at horizontal wavelengths down to at least 250 km, corresponding to spherical harmonic degree n ≈ 160. The LCS-1 vertical component and field intensity anomaly maps at Earth's surface show similar features to those exhibited by the WDMAM2 and EMM2015 lithospheric field models truncated at degree 185 in regions where they include near-surface data and provide unprecedented detail where they do not. Example regions of improvement include the Bangui anomaly region in central Africa, the west African cratons, the East African Rift region, the Bay of Bengal, the southern 90°E ridge, the Cretaceous quiet zone south of theWalvis Ridge and the younger parts of the South Atlantic.
|Number of pages||17|
|Journal||Geophysical Journal International|
|State||Published - 2017|
Bibliographical noteFunding Information:
We would like to thank Patrick Alken, Mike Purucker and an anonymous reviewer for their constructive comments on an earlier version of the manuscript. The support of the CHAMP mission by the German Aerospace Center (DLR) and the Federal Ministry of Education and Research is gratefully acknowledged.We would like to thank European Space Agency (ESA) for providing prompt access to the Swarm L1b data, and Peter Milligan for making available the Australian aeromagnetic data. DR is grateful for support from NASA grants NNX16AJ99G and NNX16AN51G.
© The Authors 2017.
- Composition and structure of the continental crust
- Composition and structure of the oceanic crust
- Inverse theory
- Magnetic anomalies: modelling and interpretation
- Satellite magnetics
- Spatial analysis
ASJC Scopus subject areas
- Geochemistry and Petrology