Physical Calibrations of the FREND Instrument Installed Onboard TGO Martian Orbiter

— The article presents results of ground calibrations of the FREND neutron telescope installed onboard the TGO spacecraft of the Russian-European ExoMars project. The main goal of the FREND space experiment is to measure hydrogen content in the subsurface layer of Mars to a depth of 1 m. High resolution maps of water mass fraction in the regolith are constructed based on these measurements. During ground physical calibrations, assessments of effective areas and measurements of angular sensitivity functions were obtained for each of the five FREND detectors. We demonstrate that FREND measurement characteristics correspond to its declared scientific goals and allow detecting and investigating local areas with enhanced water/water ice concertation on the subsurface of Mars with high spatial resolution of up to 60–200 km.