scholarly journals Technical note: A revised incoming neutron intensity correction factor for soil moisture monitoring using cosmic-ray neutron sensors

2021 ◽  
Author(s):  
Magdalena Szczykulska ◽  
David Boorman ◽  
James Blake ◽  
Jonathan G. Evans
Keyword(s):  
Soil Moisture ◽  
Correction Factor ◽  
Monitoring Network ◽  
Cosmic Ray ◽  
Flood Management ◽  
Technical Note ◽  
Moisture Regime ◽  
Significant Difference ◽  
Neutron Sensors ◽  
Soil Moisture Monitoring

Abstract. The cosmic-ray neutron sensor method of soil moisture measurement is now widely used and is fundamental to the COSMOS-UK soil moisture monitoring network. The method is based on a relationship between a measured flux of neutrons and soil moisture, and requires the neutron count to be adjusted for time variations of atmospheric pressure, humidity and the incoming flux of cosmic-ray neutrons. This note describes an empirical approach to the development of a revised correction factor for the last of these. Using the revised correction factor makes a significant difference to the derived soil moisture at wetter sites. This has implications for quantifying the soil moisture regime at these sites and management decisions that depend on a proper understanding of soil moisture dynamics, such as flood management and the release of greenhouse gases.

Penetration depth of Cosmic-ray neutron sensing for soil moisture under extreme vertical soil moisture gradients in measurements and modelling

2021 ◽  
Author(s):  
Lena M. Scheiffele ◽  
Jannis Weimar ◽  
Daniel Rasche ◽  
Benjamin Fersch ◽  
Sascha E. Oswald
Keyword(s):  
Soil Moisture ◽  
Sensor Network ◽  
Penetration Depth ◽  
Transport Model ◽  
Neutron Transport ◽  
Soil Column ◽  
Weighted Average ◽  
Monitoring Network ◽  
Cosmic Ray ◽  
Soil Moisture Monitoring

<p>Cosmic-Ray Neutron Sensing (CRNS) delivers an integral value of soil moisture over a radial footprint of 150 to 240 m and a penetration depth of 15 to 83 cm. The support volume, especially in the vertical extent, decreases with increasing soil moisture. As the sensor is most sensitive to upper soil layers and the signal contribution decreases with increasing depth, the vertical distribution of moisture influences the signal received by the neutron detector. Additional soil moisture measurements are required to estimate the penetration depth of the CRNS measurement. These may be provided by profile measurements of a soil moisture monitoring network equipped with buried electromagnetic sensors. Different horizontal and vertical weighting schemes exist to compare the integrated CRNS value to an integrated (weighted) average value from a sensor network by adjusting reference measurements to the spatial sensitivity of the sensor. The vertical weighting was developed based on hydrodynamic modelling of a soil column and a neutron transport model (MCNPx). Since then the development of the Ultra Rapid Adaptable Neutron-Only Simulation (URANOS) opened up the possibilities for more complex neutron simulations to understand and interpret the CRNS signal. Simulations confirmed the large influence of soil moisture on the penetration depth of the sensor for homogeneous vertical soil moisture distributions, rarely occurring in natural environments. While in recent years the influence of horizontal heterogeneities on the signal generation was the focus of several studies, the influence of vertical gradients achieved less attention.</p><p>Against this background, we evaluate data from a field site in southern Germany with clayey soils and influence of shallow groundwater, where a CRNS is operated in parallel to a soil moisture monitoring network. We observe a good match between the time series of CRNS derived soil moisture and the weighted soil moisture from the sensor network during infiltration events. Several times during summer, however, topsoil dries and a strong vertical gradient develops (0.20 m³ m<sup>-</sup>³ in 5 cm to 0.50 m³ m<sup>-</sup>³ in 20 cm depth). During these periods the weighted sensor network underestimates CRNS derived soil moisture by up to 0.25 m³ m<sup>-</sup>³. We hypothesize, that the estimation of the penetration depth does not hold for these extreme soil moisture gradients and that neutrons penetrate deeper into the soil and probe the wetter layers. The combination of observed neutron intensities as well as dedicated neutron transport simulations using the URANOS and MNCP6 model code will help to understand the site-specific signal behavior, explain differences observed in the data and lastly, gain information on the behavior of neutron intensities under vertically varying soil moisture contents.</p>

scholarly journals The Murrumbidgee soil moisture monitoring network data set

2012 ◽  
Vol 48 (7) ◽  
Author(s):  
A. B. Smith ◽  
J. P. Walker ◽  
A. W. Western ◽  
R. I. Young ◽  
K. M. Ellett ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Monitoring Network ◽  
Network Data ◽  
Data Set ◽  
Soil Moisture Monitoring

Useful Drainage Estimates Obtained from a Large-Scale Soil Moisture Monitoring Network by Applying the Unit-Gradient Assumption

2017 ◽  
Vol 16 (6) ◽  
pp. vzj2017.01.0016 ◽  
Author(s):  
Briana M. Wyatt ◽  
Tyson E. Ochsner ◽  
Christopher A. Fiebrich ◽  
Christopher R. Neel ◽  
David S. Wallace
Keyword(s):  
Soil Moisture ◽  
Large Scale ◽  
Monitoring Network ◽  
Soil Moisture Monitoring

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

2015 ◽  
Vol 51 (7) ◽  
pp. 5772-5790 ◽  
Author(s):  
M. Köhli ◽  
M. Schrön ◽  
M. Zreda ◽  
U. Schmidt ◽  
P. Dietrich ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Cosmic Ray ◽  
Field Scale ◽  
Soil Moisture Monitoring

scholarly journals Multiscale soil moisture estimates using static and roving cosmic-ray soil moisture sensors

2017 ◽  
Author(s):  
David McJannet ◽  
Aaron Hawdon ◽  
Brett Baker ◽  
Luigi Renzullo ◽  
Ross Searle
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Critical Role ◽  
Cosmic Ray ◽  
Process Models ◽  
Soil Moisture Sensors ◽  
Property Scale ◽  
Neutron Sensors ◽  
Local Farm ◽  
Soil Moisture Variability

Abstract. Soil moisture plays a critical role in land surface processes and as such there has been a recent increase in the number and resolution of satellite soil moisture observations and development of land surface process models with ever increasing resolution. Despite these developments, validation and calibration of these products has been limited because of a lack of observations at corresponding scales. A recently developed mobile soil moisture monitoring platform, known as the rover, offers opportunities to overcome this scale issue. This paper describes a research project aimed at producing soil moisture estimates at a range of scales that are commensurate with model and satellite retrievals. Our investigation involved static cosmic ray neutron sensors and rover surveys across both broad (36 × 36 km at 9 km resolution) and intensive (10 × 10 km at 1 km resolution) scales in a cropping district in the Mallee region of Victoria, Australia. We describe approaches for converting rover survey neutron counts to soil moisture and discuss the factors controlling soil moisture variability. Measurements revealed that temporal patterns in soil moisture were preserved through time and regression modelling approaches were utilised to produce time series of property scale soil moisture which may also have application in calibration and validation studies or local farm management. Intensive scale rover surveys produced reliable soil moisture estimates at 1 km resolution while broad scale surveys produced soil moisture estimates at 9 km resolution. We conclude that the multiscale soil moisture products produced in this study are well suited to future analysis of satellite soil moisture retrievals and finer scale soil moisture models.

scholarly journals Use of cosmic ray neutron sensors for soil moisture monitoring in forests

2015 ◽  
Vol 12 (9) ◽  
pp. 9813-9864 ◽  
Author(s):  
I. Heidbüchel ◽  
A. Güntner ◽  
T. Blume
Keyword(s):  
Time Series ◽  
Soil Moisture ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Cosmic Ray ◽  
Soil Samples ◽  
Calibration Function ◽  
Neutron Sensors ◽  
Hydrogen Mass

Abstract. Cosmic ray neutron sensors (CRS) are a promising technique to measure soil moisture at intermediate scales. To convert neutron counts to average volumetric soil water content a simple calibration function can be used (the N0-calibration of Desilets et al., 2010). This calibration function is based on soil water content derived directly from soil samples taken within the footprint of the sensor. We installed a CRS in a mixed forest in the lowlands of north-eastern Germany and calibrated it 10 times throughout one calendar year. Each calibration with the N0-calibration function resulted in a different CRS soil moisture time series, with deviations of up to 0.12 m3 m-3 for individual values of soil water content. Also, many of the calibration efforts resulted in time series that could not be matched with independent in situ measurements of soil water content. We therefore suggest a new calibration function with a different shape that can vary from one location to another. A two-point calibration proved to be adequate to correctly define the shape of the new calibration function if the calibration points were taken during both dry and wet conditions covering at least 50 % of the total range of soil moisture. The best results were obtained when the soil samples used for calibration were linearly weighted as a function of depth in the soil profile and non-linearly weighted as a function of distance from the CRS, and when the depth-specific amount of soil organic matter and lattice water content was explicitly considered. The annual cycle of tree foliation was found to be a negligible factor for calibration because the variable hydrogen mass in the leaves was small compared to the hydrogen mass changes by soil moisture variations. Finally, we provide a best practice calibration guide for CRS in forested environments.

scholarly journals Intercomparison of Cosmic-Ray Neutron Sensors andWater Balance Monitoring in an Urban Environment

2017 ◽  
Author(s):  
Martin Schrön ◽  
Steffen Zacharias ◽  
Gary Womack ◽  
Markus Köhli ◽  
Darin Desilets ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Large Scale ◽  
Neutron Transport ◽  
Cosmic Ray ◽  
Environmental Water ◽  
Integration Time ◽  
Multiple Sensors ◽  
Neutron Count ◽  
Urban Terrain ◽  
Neutron Sensors

Abstract. Sensor-to-sensor variability is a source of error common to all geoscientific instruments, which needs to be assessed before comparative and applied research can be performed with multiple sensors. Consistency among sensor systems is especially critical when the signal is an integral value that covers a large volume within complex, urban terrain. Cosmic-Ray Neutron Sensors (CRNS) are a recent technology that is used to monitor large-scale environmental water storages, for which a rigorous comparison study of numerous co-located sensors has never been performed. In this work, nine stationary CRNS probes of type CRS1000 were installed in relative proximity on a grass patch surrounded by complex urban terrain. While the dynamics of the neutron count rates were found to be similar, offsets of a few percent from the absolute average neutron count rates were found. Technical adjustments of the individual detection parameters brought all instruments into good agreement. Furthermore, the arrangement of multiple sensors allowed to find a critical integration time of 6 hours above which all sensors showed consistent dynamics in the data and their RMSE fell below 1 % of gravimetric water content. The residual differences between the nine signals indicated local effects of the complex urban terrain at the scale of several meters. Mobile CRNS measurements and spatial neutron transport simulations in the surrounding area (25 ha) have revealed that CRNS detectors are sensitive to sub-footprint heterogeneity despite their large averaging volume. The paved and sealed areas in the footprint furthermore damp the dynamics of the CRNS soil moisture product. We developed strategies to correct for the sealed-area effect based on theoretical insights about the spatial sensitivity of the sensor. This procedure not only led to reliable soil moisture estimation in drying periods, it further revealed a strong signal of interception and evaporation water that emerged over the sealed ground during and shortly after rain events. The presented arrangement offered a unique opportunity to demonstrate the CRNS performance in complex terrain, and the results indicate great potential for further applications in urban water sciences.

scholarly journals Multiscale soil moisture estimates using static and roving cosmic-ray soil moisture sensors

2017 ◽  
Vol 21 (12) ◽  
pp. 6049-6067 ◽  
Author(s):  
David McJannet ◽  
Aaron Hawdon ◽  
Brett Baker ◽  
Luigi Renzullo ◽  
Ross Searle
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Critical Role ◽  
Cosmic Ray ◽  
Process Models ◽  
Soil Moisture Sensors ◽  
Property Scale ◽  
Neutron Sensors ◽  
Local Farm ◽  
Soil Moisture Variability

Abstract. Soil moisture plays a critical role in land surface processes and as such there has been a recent increase in the number and resolution of satellite soil moisture observations and the development of land surface process models with ever increasing resolution. Despite these developments, validation and calibration of these products has been limited because of a lack of observations on corresponding scales. A recently developed mobile soil moisture monitoring platform, known as the rover, offers opportunities to overcome this scale issue. This paper describes methods, results and testing of soil moisture estimates produced using rover surveys on a range of scales that are commensurate with model and satellite retrievals. Our investigation involved static cosmic-ray neutron sensors and rover surveys across both broad (36 × 36 km at 9 km resolution) and intensive (10 × 10 km at 1 km resolution) scales in a cropping district in the Mallee region of Victoria, Australia. We describe approaches for converting rover survey neutron counts to soil moisture and discuss the factors controlling soil moisture variability. We use independent gravimetric and modelled soil moisture estimates collected across both space and time to validate rover soil moisture products. Measurements revealed that temporal patterns in soil moisture were preserved through time and regression modelling approaches were utilised to produce time series of property-scale soil moisture which may also have applications in calibration and validation studies or local farm management. Intensive-scale rover surveys produced reliable soil moisture estimates at 1 km resolution while broad-scale surveys produced soil moisture estimates at 9 km resolution. We conclude that the multiscale soil moisture products produced in this study are well suited to future analysis of satellite soil moisture retrievals and finer-scale soil moisture models.

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