Validation of the MERLIN data products by the airborne demonstrator CHARM-F is regarded a key mission element. Deployment of this instrument on the German HALO or French ATR aircrafts during several scientific campaigns enabled to improve the measurement performance and data reduction capability, enormously. Thus CHARM-F is on the right track to meet the stringent measurement requirements for MERLIN. It is found that the systematic error of CHARM-F can be kept smaller than 3 ppb which is the target performance requirement for MERLIN. Preliminary direct comparisons to WMO certified In-Situ measurements, however, show still an almost constant bias of about 1.5 % which is subject to further investigations.
Zechlau et al. (Thu,) studied this question.