eprintid: 34407
rev_number: 22
eprint_status: archive
userid: 4612
dir: disk0/00/03/44/07
datestamp: 2024-02-07 10:07:28
lastmod: 2024-02-12 11:48:27
status_changed: 2024-02-07 10:07:28
type: article
metadata_visibility: show
creators_name: Köhli, Markus
creators_name: Schrön, Martin
creators_name: Zreda, Marek
creators_name: Schmidt, Ulrich
creators_name: Dietrich, Peter
creators_name: Zacharias, Steffen
title: Footprint characteristics revised for field-scale soil moisture monitoring with cosmic-ray neutrons
subjects: ddc-530
divisions: i-130200
divisions: i-130500
keywords: COSMOS detector, energy spectrum, neutron transport model, soil water content, spatially weighted average, support volume
abstract: 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.
date: 2015
publisher: Wiley
id_scheme: DOI
id_number: 10.11588/heidok.00034407
official_url: https://doi.org/10.1002/2015WR017169
ppn_swb: 1880516969
own_urn: urn:nbn:de:bsz:16-heidok-344079
language: eng
bibsort: KOHLIMARKUFOOTPRINTC20150818
full_text_status: public
publication: Water Resources Research
volume: 51
number: 7
place_of_pub: Hoboken, NJ
pagerange: 5772-5790
issn: 1944-7973
edition: Zweitveröffentlichung
citation:   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     
document_url: https://archiv.ub.uni-heidelberg.de/volltextserver/34407/7/Footprint_characteristics%20_revised_2015.pdf