Figure 12.1: Evolution of the parameters β4 and β5 , describing the relative amplitude
and phase of the second harmonic in the modulated signal, over the mission. The
vertical lines represent changes in focal plane position. The discontinuity visible at
day 755 is due to a thermal-control failure and change of thermal control electronics.
The top curve in each graph refers to the following, the lower curve to the preceding
FOV.