A cosmic-ray soil moisture probe is usually calibrated locally using soilsamples collected within its support volume. But such calibration may bedifficult or impractical, for example when soil contains stones, in presenceof bedrock outcrops, in urban environments, or when the probe is used as arover. Here we use the neutron transport code MCNPx with observed soilchemistries and pore water distribution to derive a universal calibrationfunction that can be used in such environments. Reasonable estimates of porewater content can be made from neutron intensity measurements and by using measurements of the other hydrogen pools (water vapor,soil lattice water, soil organic carbon, and biomass). Comparisons withindependent soil moisture measurements at one cosmic-ray probe site and,separately, at 35 sites, show that the universal calibration functionexplains more than 79% of the total variability within each dataset,permitting accurate isolation of the soil moisture signal from the measuredneutron intensity signal. In addition the framework allows for any of theother hydrogen pools to be separated from the neutron intensity measurements,which may be useful for estimating changes in biomass, biomass water, orexchangeable water in complex environments.
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