Footprint characteristics revised for field‐scale soil moisture monitoring with cosmic‐ray neutrons

By M. Kohli, M. Schron, Marek Zreda, U. Schmidt, Peter Dietrich, S. Institut, H. University, Department of Monitoring, Exploration Technologies, Ufz Leipzig and 3 more. 2015

304 citations recorded by the source corpus.

Cosmic‐ray neutron probes are widely used to monitor environmental water content near the surface. The method averages over tens of hectares and is unrivaled in serving representative data for agriculture and hydrological models at the hectometer scale. Recent experiments, however, indicate that the sensor response to environmental heterogeneity is not fully understood. Knowledge of the support volume is a prerequisite for the proper interpretation and validation of hydrogeophysical data. In a previous study, several physical simplifications have been introduced into a neutron transport model in order to derive the characteristics of the cosmic‐ray probe's footprint. We utilize a refined source and energy spectrum for cosmic‐ray neutrons and simulate their response to a variety of environmental conditions. Results indicate that the method is particularly sensitive to soil moisture in the first tens of meters around the probe, whereas the radial weights are changing dynamically with ambient water. The footprint radius ranges from 130 to 240 m depending on air humidity, soil moisture, and vegetation. The moisture‐dependent penetration depth of 15 to 83 cm decreases exponentially with distance to the sensor. However, the footprint circle remains almost isotropic in complex terrain with nearby rivers, roads or hill slopes. Our findings suggest that a dynamically weighted average of point measurements is essential for accurate calibration and validation. The new insights will have important impact on signal interpretation, sensor installation, data interpolation from mobile surveys, and the choice of appropriate resolutions for data assimilation into hydrological models.

Subfields: Civil and Structural Engineering, Environmental Engineering, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/8136ba7f3517948d9c0b055883e8795b6da3e172

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Civil and Structural Engineering

1. Rafael Rosolem
2. Juliane Mai
3. Steffen Zacharias

In Environmental Engineering

1. U. Schmidt
2. Rafael Rosolem
3. Peter Dietrich
4. Steffen Zacharias

In Global and Planetary Change

1. Rafael Rosolem
2. Corinna Rebmann
3. Juliane Mai

Citations in the corpus

• Improving calibration and validation of cosmic-ray neutron sensors in the light of spatial sensitivity (2017, methodology): “As the understanding of cosmic-ray neutron physics in the environment has been more and more elaborated, Köhli et al. (2015) developed a dedicated computer model, URANOS, which helped to understand the spatial sensitivity of the neutron sensor.”