Geomagnetism

Magnetic Field Model MF5

Six years of low-orbit CHAMP satellite magnetic measurements have provided an exceptionally high-quality data resource for lithospheric magnetic field modeling. Our fifth generation satellite-only magnetic field model MF5 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 and can be safely 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. The new MF5 model was produced in a very similar way to the previous MF4 model. The aim of keeping the model noise-free up to degree 100 was achieved by two improvements: The first was to use only the latest three years of CHAMP scalar and vector measurements. This has the advantage of a lower flight altitude. But it also makes the altitude distribution more homogeneous. CHAMP was lifted several times in the past years, and its orbit has become even less eccentric. This homogeneous altitude distribution helps in the second improvement, a better line-leveling. The evolution from MF1 over MF3 to MF5 is shown for a low-latitude area in Figure 1, and for a high-latitude (noisy) area in Figure 2.

Fig. 1: The low latitudes are relatively quiet at night-time during undisturbed periods, making it easier to map the magnetic field. As shown for the example of India, there is a steady improvement in resolution from MF1 to MF5.

Fig. 2: The region between Antarctica and Australia is most difficult to map because the auroral oval extends to very low latitudes here, while the crustal signal is rather weak. The reduced level of North/South trending noise in MF5 was achieved by using a line-leveling technique.

Available MF5 Downloads
	Type	Format	Mbyte	Ref. Radius	Contents
	SH coefficients	ASCII Table	0.2	6371.2 km	MF5 Model spherical harmonic coefficients (Schmid semi-normalized, as usual)
	Article	PDF	0.6		Fifth generation lithospheric magnetic field model from CHAMP satellite measurements
	Graphic	JPG	14	Geoid	Image of anomaly of total intensity at geoid altitude.
	Graphic	JPG	6	Geoid	Image of vertical component (Z) at geoid altitude.
	Listing	ZIP	6	Geoid	MF5_F_0.xyz.zip Ascii grid of anomaly of total intensity at geoid altitude.
	Listing	ZIP	6	Geoid	MF5_Z_0.xyz.zip Ascii grid of magnetic field vertical component (Z) at geoid altitude.
	Listing	ZIP	6	6771.2 km	MF5_400_as.xyz.zip Ascii grid of the analytic signal at 400 km altitude.
	Listing	ZIP	6	6771.2 km	MF5_400_dFdx.xyz.zip Ascii grid of the northward derivative of the total intensity anomaly at 400 km altitude.
	Listing	ZIP	6	6771.2 km	MF5_400_dF_dy.xyz.zip Ascii grid of the eastward derivative of the total intensity anomaly at 400 km altitude.
	Listing	ZIP	6	6771.2 km	MF5_400_dFdz.xyz.zip Ascii grid of the downward derivative of the total intensity anomaly at 400 km altitude.
	Animation	MPEG	23	6421.2 km	Animation showing the vertical component at r=6772.2 km for a single, rotating Earth.
	Animation	MPEG	27	6421.2 km	Animation showing the vertical component at r=6421.2 km for South and North Polar views, side by side.

2006-Oct-25, Stefan Maus