Following discussions on the behaviour of the magnetic data from Swarm particularly in 2017 the scaling parameterisation of the VFM instrument has been revisited. Using data from BOM until 1. June 2017 two different methods of VFM scaling have been tested: an exponential decaying sensitivity (which was applied on the Advanced version 0501 L1b magnetic data) and a piece-wise linear (in time) sensitivity. Below the scalar residual plots following the two methods are shown for satellites Alpha and Bravo. For the exponential decay there are indications of poorer performance in late 2016 and 2017 whereas the linear scaling does not show any clear systematic variations with time.
The actual VFM scalings applied in the two methods are compared in the plots below. The scalings are detrended such that the last part of the linear scaling is horizontal. As can be seen, the actual differences in the applied scalings are moderate but nevertheless, the effect is visible in the residual plots above, in particular for Swarm Alpha.
