Monitoring of Snowpack Dynamics With Cosmic-Ray Neutron Probes: A Comparison of Four Conversion Methods

Bogena, Heye; Herrmann, Frank; Jakobi, Jannis; Brogi, Cosimo; Ilias, Andreas; Huisman, Johan Alexander; Παναγόπουλος, Ανδρέας; Pisinaras, Vassilios

doi:10.3389/frwa.2020.00019

Cited by 27 publications

(42 citation statements)

References 53 publications

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“…If the only exhibits little change to changes in soil moisture. This estimate comes close to what is stated in Bogena et al (2020). In our simulations with constant soil moisture in near field mineral soils, the fraction of detected neutrons being thermalized in areas covered with mineral soils and peatland soils remains constant although soil moisture in peatland soils is altered (Fig.…”

Section: Neutron Energy-dependent Variations Of Footprint Size and Neutron Intensitysupporting

confidence: 91%

“…In contrast, little is known about the measurement footprint radius of thermal neutrons. Previous studies assume a similarly sized footprint (e.g., Vather et al, 2020) or a significantly smaller measurement radius (e.g., Bogena et al, 2020). Our simulation results reveal that the derived measurement radii strongly depend on the definition of the point of origin of the thermal neutrons detected by the virtual neutron detector.…”

Section: Neutron Energy-dependent Variations Of Footprint Size and Neutron Intensitymentioning

confidence: 59%

“…Although neutrons in the epithermal energy range are the basis for deriving soil moisture contents, thermal neutrons remain in the focus of CRNS research as they can provide valuable information for estimating biomass (e.g., Tian et al, 2016;Jakobi et al, 2018;Vather et al, 2020) or snow water equivalent (SWE) (Bogena et al, 2020), e.g. by using the ratio of epithermal and thermal neutrons.…”

mentioning

confidence: 99%

“…Considering different footprint sizes of thermal and epithermal neutrons, a combination of both through calculating neutron ratios requires all hydrogen to be distributed homogeneously in the measurement footprints. As a result uncertainties may arise when hydrogen is not distributed homogeneously in the footprints as mentioned by Bogena et al (2020) and this limits the applicability of combining thermal and epithermal neutrons. This may be of particular importance as most studies with stationary CRNS assume homogeneous site conditions.…”

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confidence: 99%

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Towards disentangling heterogeneous soil moisture patterns in Cosmic-Ray Neutron Sensor footprints

Rasche

Köhli

Schrön

et al. 2021

Preprint

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Abstract. Cosmic-Ray Neutron Sensing (CRNS) allows for non-invasive soil moisture measurements at the field scale. The derivation of soil moisture generally relies on secondary cosmic-ray neutrons in the epithermal-to-fast energy range. Most approaches and processing techniques for observed neutron intensities are based on the assumption of homogeneous site conditions within the measurement footprint of the neutron detector. In this study we investigated how a non-uniform soil moisture distribution within the footprint impacts the CRNS soil moisture estimation and how the combined use of epithermal and thermal neutrons can be advantageous in this case. Thermal neutrons have lower energies and a substantially smaller measurement footprint around the sensor than epithermal neutrons. Analyses using URANOS neutron Monte-Carlo simulations to investigate measurement footprint dynamics at a study site in north-eastern Germany revealed that the thermal footprint mainly covers mineral soils in the near-field to the sensor while the epithermal footprint also covers large areas with organic soils. We found that either combining the observed thermal and epithermal neutron intensities by a rescaling method developed in this study, or adjusting all parameters of the transfer function leads to an improved calibration against reference soil moisture measurements in the near field compared to the standard approach and using epithermal neutrons alone. We also found that the relationship between thermal and epithermal neutrons provided an indicator for footprint heterogeneity. We therefore suggest that the combined use of thermal and epithermal neutrons offers the potential of a spatial discretization of the measurement footprint in terms of near and far field soil moisture dynamics.

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Section: Neutron Energy-dependent Variations Of Footprint Size and Neutron Intensitysupporting

confidence: 91%

Section: Neutron Energy-dependent Variations Of Footprint Size and Neutron Intensitymentioning

confidence: 59%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Towards disentangling heterogeneous soil moisture patterns in Cosmic-Ray Neutron Sensor footprints

Rasche

Köhli

Schrön

et al. 2021

Preprint

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“…CC BY 4.0 License. inversely correlated with the amount of hydrogen in the soil (Zreda et al 2008;Andreasen et al, 2017) or snow cover (Desilets et al 2010;Gottardi et al, 2013;Sigouin and Si, 2016;Bogena et al, 2020). Even though the principle of this approach has been known since the 1970s, it attained a level of operational maturity in the 2000s, especially with the use of commercialized soil moisture probes.…”

Section: Cosmic Ray Neutron Probe (Crnp)mentioning

confidence: 99%

Review article: Performance assessment of electromagnetic wave-based field sensors for SWE monitoring

Royer

Roy

Jutras

et al. 2021

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Abstract. Continuous and spatially distributed data of snow mass (snow water equivalent, SWE) from automatic ground-based measurements are increasingly required for climate change studies and for hydrological applications (snow hydrological model improvement and data assimilation). We present and compare four new-generation non-invasive sensors that are based on electromagnetic waves for direct measurements of SWE: Cosmic Ray Neutron Probe (CNRP); Gamma Ray Monitoring (GMON) scintillator; frequency-modulated continuous-wave radar (FMCW-Radar) at 24 GHz; and Global Navigation Satellite System (GNSS) receivers for SWE retrieval. All four techniques are relatively low cost, have low power requirements, provide continuous and autonomous measurements, and can be installed in remote areas. Their operating principles are briefly summarized before examples of comparative measurements are provided. A performance review comparing their advantages, drawbacks and accuracies is discussed. Overall instrument accuracy is estimated to range between 9 and 15 %.

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The footprint characteristics of cosmic ray thermal neutrons

Jakobi

Huisman

Köhli

et al. 2021

Preprint

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Cosmic ray neutron (CRN) sensing is a non-invasive method for intermediate scale soil moisture measurements (Zreda et al., 2008). This method relies on the inverse dependence of aboveground epithermal neutrons (energy range from ∼0.5 eV to 100 keV) on the environmental hydrogen content in a footprint of 130-240 m radius and soil depths ranging from 15 to 83 cm (Köhli et al., 2015;Schrön et al., 2017). In terrestrial environments, most hydrogen is stored in water in soils. Therefore, it is possible to infer soil moisture content from the amount of aboveground epithermal neutrons. Secondary hydrogen pools, such as biomass, have a large impact on the measurement accuracy, especially when they are not constant in time. For reliable soil moisture estimation, these secondary pools thus need to be considered (Baatz et al., 2014;Bogena et al., 2013;. Recently, it was found that by additionally considering the thermal neutron intensity below ∼0.5 eV, aboveground biomass can be inferred using the ratio of thermal to epithermal neutrons (Jakobi et al., 2018;Tian et al., 2016).CRN sensors are currently installed in approximately 200 locations worldwide (Andreasen et al., 2017). Many of these locations are also instrumented with thermal neutron detectors. However, these extensive data sets are rarely explored because key properties of the thermal neutron signal, such as the footprint of thermal neutrons, are not well defined. Preliminary investigations suggest that the thermal neutron footprint is smaller than the epithermal neutron footprint and in the order of tens of meters (Bogena et al., 2020). For

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Monitoring of Snowpack Dynamics With Cosmic-Ray Neutron Probes: A Comparison of Four Conversion Methods

Cited by 27 publications

References 53 publications

Towards disentangling heterogeneous soil moisture patterns in Cosmic-Ray Neutron Sensor footprints

Towards disentangling heterogeneous soil moisture patterns in Cosmic-Ray Neutron Sensor footprints

Review article: Performance assessment of electromagnetic wave-based field sensors for SWE monitoring

The footprint characteristics of cosmic ray thermal neutrons

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