To provide magnetometer data suitable for scientific study, the calibration step is essential.  The full calibration process involves a calibration campaign carried out on the ground before launch followed by constant in-flight calibration after the launch. 

The figures below show spectrograms for a complete orbit before and after adjustment of the calibration parameters. In both cases, the instrument range is indicated by the solid red or white line. For each orbit, the range transitions from 4->3->2->3->4, with most of the time spent in Range 2.

Can you spot the difference?

In the first plot, unacceptable levels of spin-frequency signal and harmonics in Range 3 can be seen.  The fundamental of the spin frequency is 0.25 Hz (1 revolution of the spacecraft approximately every 4 seconds). This indicates that the calibration parameters are not optimised. After adjustment, the spin-tone is reduced to an acceptable level, as shown in the second plot.

Further details of the solutions to the main calibration issues which lead to final data products of the highest quality can be found in the links below.

• Description of the calibration problem
• In-flight calibration techniques