Most studies using cosmic-ray neutron sensors (CRNS) for soil moisture estimation use high-energy neutron monitor observations to correct for changes in incoming neutron intensity, but there is interest in over-water CRNS observations and muon observations for such purposes. This study compares these approaches with a focus on observations from an over-water pontoon-based CRNS system. Pontoon and neutron monitor intensity comparisons showed similar responses with the best statistical agreement when neutron monitor observations were from locations of similar cutoff rigidity or when scaling for geomagnetic and elevational effects were applied. Comparison of historic variations in neutron monitor and muon detector intensity, and more recent observations from the pontoon, revealed temporal differences and weaker short-term responses from the muon detector. Time-delays in intensity correction for the pontoon and neutron monitors were observed during a Forbush decrease and through cross-correlation analysis over the comparison period with delays likely a result of longitudinal differences. Pontoon neutron intensity exhibited slightly higher amplitudes over the study period. Some of this was related to periods of irregular water vapour distribution in the atmosphere where current humidity corrections appear insufficient. Application of intensity corrections to soil moisture estimates illustrated the increasing importance of accurate corrections with decreasing cutoff rigidity and increasing elevation. The impact of neutron intensity correction was greatest for wet soil conditions at low cutoff rigidity sites at higher elevations. Over-water CRNS observations offer a means to correct CRNS observations with the advantages of being locally managed, locally applicable, and directly relevant to CRNS energy spectra.

The higher elevation forests of Norfolk Island are regularly immersed in the clouds and scientific and anecdotal evidence suggests that in addition to rainfall, water is likely to be collected as cloud droplets are intercepted by the forest canopy. This water is likely to be important for the local hydrology and ecology, yet it has never been quantified. To address this, a field measurement campaign was established to measure hydrological inputs to the forest floor at two elevated forest sites in the Norfolk Island National Park. Instrumentation included throughfall and stemflow systems and measurements of rainfall in the open in nearby clearings. Sites exhibited very high stem density and basal area by international standards and delivery of water to the forest floor was dominated by stemflow because of the funnelling characteristics of the dominant palm and pine trees. Both sites showed similar hydrological behaviour with stemflow and throughfall of around 48% and 32%, respectively. Stemflow contributions of 48% far exceed observations from the literature which are typically less than 10%. Rainfall rarely occurred in the absence of low-level cloud and some cloud immersion events lasted for many days with hydrologic inputs continuing for extended periods despite rainfall not being observed in the open. Cloud interception accounted for approximately 20% of total water input at both sites which is equivalent to 25% extra water on top of rainfall measured in the open. From an island-wide perspective the calculated extra hydrological input is only small due to the limited spatial extent of elevated forest, however, the additional water is likely to be very important to local hydrological processes and the unique plants, insects and animals which inhabit the higher elevation forests of Norfolk Island.