A comparison of CHAMP and Ørsted Main and External Field Models for 2001

Spherical harmonic models of the Earth’s magnetic field up to degree 13 internal and 2 external are constructed separately from CHAMP and Ørsted satellite data sets for epoch 2001.5. Only night side measurements on quiet days between May and October 2001 are used. Quiet times are determined from the Kp (typically Kp < 2) and Dst (|Dst| < 20) indices. Observations are made on the relative satellite data quality, as well as the data distributions in local time, latitude and longitude and the degree of model consistency for this period. Prior to a final CHAMP vector calibration, we consider the possibility of merging the two satellite data sets.