Abstract

Ground-based neutron monitors (NM64) are the standard for tracking heliospheric modulation, yet their integral count rates are susceptible to bias from local environmental moderation (e.g., soil moisture, snow). To decouple these local effects from primary cosmic-ray variations, we present the deployment of the portable CEFNEN neutron spectrometer at Las Campanas Observatory (2320 m.a.s.l., Chile). The instrument, based an array of up to 16 moderated 3He detectors (11 utilized in this campaign), retrieves the cosmic-ray neutron spectrum with 15-minute temporal resolution. A key finding is that the spectral ratio R = ith/(iep + ifs) provides a model-independent proxy for near field hydrogen content. Because this ratio is dominated by multiply-scattered neutrons detected with moderate geometric anisotropy (K approximate to 1.3), angular effects largely cancel making R robust across isotropic, directional, mixed unfolding hypotheses. During a rapid snow precipitation event, R increased by +34% to +43%, tracking thermal flux enhancement (+20% to +24%) and epithermal suppression (-17% to-18%), all exceeding significance regardless of the angular treatment assumed. While the absolute high-energy flux shows a factor of-two sensitivity to these assumptions (affecting dosimetric estimates spanning H*(10) approximate to 31-64 nSv h-1), environmental signatures remain unambiguous. A dedicated geometric analysis reveals that the high-energy monitor exhibits an anisotropy ratio K = explaining the enhanced sensitivity to the downward cosmic-ray cascade. The barometric pressure correction uses beta LCO = 6.94 & times;10-3 mbar-1, estimated from the geomagnetic cutoff rigidity of the site (RC approximate to 10.5 GV) via empirical relation from literature. We conclude that R serves as a robust correction factor for environmental effects at neutron monitor stations, independent of assumptions about the angular distribution of the incident cosmic-ray field.