The flights of the civil part (ARM21c) of the exercise were performed between June 28^th and July 2^nd and the flights of the military part (ARM21m) were performed between August 30^th and September 2^nd, 2021.
Both parts of the exercise included the measurement of an altitude profile over Lake Neuchâtel with sufficient altitude range to determine the slope of the altitude dependent cosmic correction.
According to the alternating schedule of the annual ARM exercises, the environs of the nuclear power plants Gösgen (KKG) and Mühleberg (KKM) were surveyed, the former extended with an area to the south-east of the power plant. The measurements showed no artificial radionuclides outside of the plant premises.
The series of background measurements over Swiss cities was continued with flights over Frauenfeld, Lugano, Nyon and Wil.
As a follow-up of the Caesium deposition in the wake of the Chernobyl accident, measurements were performed over areas in western and southern Switzerland. Residual 137Cs activity can still be detected in the vicinity of Lugano and several other sites tested during ARM21 as a follow-up of the Chernobyl deposition. Comparison to results of ground measurements, maps published in the scientific literature and previous airborne measurements yielded reasonable agreement to the measurement results.
Detector RLL001 used in ARM21c continues to operate as specified. Problems with one NaI(Tl) crystal of detector RLL004 used during ARM21m indicates that not all of the crystals with poor quality have been identified in previous exercises.