title: Footprint characteristics revised for field-scale soil moisture monitoring with cosmic-ray neutrons
creator: Köhli, Markus
creator: Schrön, Martin
creator: Zreda, Marek
creator: Schmidt, Ulrich
creator: Dietrich, Peter
creator: Zacharias, Steffen
subject: ddc-530
subject: 530 Physics
description: 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.
publisher: Wiley
date: 2015
type: Article
type: info:eu-repo/semantics/article
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/34407/7/Footprint_characteristics%20_revised_2015.pdf
identifier: DOI:10.11588/heidok.00034407
identifier: https://doi.org/10.1002/2015WR017169
identifier: urn:nbn:de:bsz:16-heidok-344079
identifier:   Köhli, Markus ; Schrön, Martin ; Zreda, Marek ; Schmidt, Ulrich ; Dietrich, Peter ; Zacharias, Steffen  (2015) Footprint characteristics revised for field-scale soil moisture monitoring with cosmic-ray neutrons.  Water Resources Research, 51 (7).  pp. 5772-5790.  ISSN 1944-7973     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/34407/
rights: info:eu-repo/semantics/openAccess
rights: Please see front page of the work (Sorry, Dublin Core plugin does not recognise license id)
language: eng