Assessment of water content in martian subsurface along the traverse of the curiosity rover based on passive measurements of the DAN instrument

This paper presents the method of estimating water-equivalent hydrogen (WEH) content from neutron sensing data that were measured by the Dynamic Albedo of Neutron (DAN) instrument onboard the Curiosity rover. Analyzed data are derived from the DAN passive operations, when the instrument measures the flux of neutron albedo from the surface, which is produced by bombardment by Galactic Cosmic Rays (GCR) and irradiation from Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) installed onboard the rover. The suggested Method of Referencing by Active Data (MRAD) for the analysis of DAN passive data is compared with the previously suggested Method of Numerical Simulation (MNS, see Tate et al., 2015, Tate et al., 2018, Tate et al., 2019) for the analysis of DAN passive data: the qualitative agreement between them is shown with some systematic increase of WEH for the second one. The possible reason for that is explained in Section 6. Results for the DAN passive data analysis by MRAD are presented obtained for almost 20 km of the rover's traverse (until November 2, 2018 or sol 2218). The range of WEH average concentration of (2.6 ± 0.7) wt% is found for this part of the traverse, which is consistent with a method of active neutron sensing (Mitrofanov et al., 2014, Mitrofanov et al., 2016; Lisov et al., 2018).