TY  - JOUR
EP  - 5790
N2  - 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.
SN  - 1944-7973
TI  - Footprint characteristics revised for field-scale soil moisture monitoring with cosmic-ray neutrons
JF  - Water Resources Research
Y1  - 2015///
VL  - 51
UR  - https://doi.org/10.1002/2015WR017169
IS  - 7
PB  - Wiley
ID  - heidok34407
AV  - public
A1  - Köhli, Markus
A1  - Schrön, Martin
A1  - Zreda, Marek
A1  - Schmidt, Ulrich
A1  - Dietrich, Peter
A1  - Zacharias, Steffen
CY  - Hoboken, NJ
SP  - 5772
KW  - COSMOS detector
KW  -  energy spectrum
KW  -  neutron transport model
KW  -  soil water content
KW  -  spatially weighted average
KW  -  support volume
ER  -