SMuK 2021 – wissenschaftliches Programm

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UP: Fachverband Umweltphysik

UP 4: Measurement Techniques & Miscellaneous

UP 4.3: Vortrag

Freitag, 3. September 2021, 11:30–11:45, H7

Moisture and humidity dependence of the above-ground cosmic-ray neutron intensity revised — •Markus Köhli^1,2, Jannis Weimar¹, Martin Schrön³, and Ulrich Schmidt¹ — ¹Physikalisches Institut, Heidelberg University — ²Physikalisches Institut, University of Bonn — ³Helmholtz Centre for Environmental Research-UFZ, Leipzig

The novel method of Cosmic-ray neutron sensing (CRNS) allows non-invasive soil moisture measurements at a hectometer scaled footprint. Up to now, the conversion of soil moisture to a detectable neutron count rate relies mainly on the equation presented by Desilets et al. (2010). While in general a hyperbolic expression can be derived from theoretical considerations, their empiric parameterisation needs to be revised for two reasons. Firstly, we find a 3-parameter equation with unambiguous values equivalent to the 4-parameter equation. Secondly, high-resolution Monte-Carlo simulations revealed a systematic deviation of the count rate to soil moisture relation especially for extremely dry conditions as well as very humid conditions. That is a hint, that a smaller contribution to the intensity was forgotten or not adequately treated by the conventional approach. Investigating the above-ground neutron flux by a broad simulation campaign revealed a more detailed understanding of different contributions to this signal. The packages MCNP and URANOS were used to derive a function including the detector-specific response. The new relationship has been tested at three exemplary measurement sites and its remarkable performance allows for a promising prospect of more comprehensive data quality.