Residual Magnetic Anomalies Mapping from CHAMP Observations

Abstract

CHAMP high-quality vector magnetometer observations collected from July 2000 to September 2010 have been used to map the residual vector magnetic anomaly fields. This field is so called the lithospheric magnetic field which is the result of two contributions of the induced and the remanent magnetization. It is therefore essential to study the magnetic properties of the crustal rocks. Isolating this field from the other contributions, interpreting and even defining are however difficult and still debated. We investigate how to identify and separate the lithospheric vector magnetic field Δ X , Δ Y and Δ Z from other contributions. For this purpose we use selected night magnetic data from which we remove a model field of degree 16 and external model field of degree 2 developed by spherical harmonics analysis. Concerning the induced lithospheric field which is assumed to be aligned with the internal dipole was also removed. To minimize the secular variation effects, we calculated internal models for each two months. The method developed here has been successfully applied to isolate lithospheric field produced by remanent magnetizations from CHAMP satellite data. The resolution and altitude measurements make it very hard to map short wavelength crustal magnetic anomalies. The large-scale strong magnetic anomalies detected using this technique are in agreement with previous global magnetic maps. These anomalies appear with an amplitude of about 10 nT at satellite altitude such as Bangui’s anomaly.