The Effect of Atmospheric Water Vapor on Neutron Count in the Cosmic-Ray Soil Moisture Observing System

2013 ◽  
Vol 14 (5) ◽  
pp. 1659-1671 ◽  
Author(s):  
R. Rosolem ◽  
W. J. Shuttleworth ◽  
M. Zreda ◽  
T. E. Franz ◽  
X. Zeng ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Water Vapor ◽  
Neutron Transport ◽  
Cosmic Ray ◽  
Atmospheric Water Vapor ◽  
Fast Neutrons ◽  
Atmospheric Conditions ◽  
Atmospheric Water ◽  
Neutron Measurement ◽  
Neutron Intensity

Abstract The cosmic-ray method for measuring soil moisture, used in the Cosmic-Ray Soil Moisture Observing System (COSMOS), relies on the exceptional ability of hydrogen to moderate fast neutrons. Sources of hydrogen near the ground, other than soil moisture, affect the neutron measurement and therefore must be quantified. This study investigates the effect of atmospheric water vapor on the cosmic-ray probe signal and evaluates the fast neutron response in realistic atmospheric conditions using the neutron transport code Monte Carlo N-Particle eXtended (MCNPX). The vertical height of influence of the sensor in the atmosphere varies between 412 and 265 m in dry and wet atmospheres, respectively. Model results show that atmospheric water vapor near the surface affects the neutron intensity signal by up to 12%, corresponding to soil moisture differences on the order of 0.10 m3 m−3. A simple correction is defined to identify the true signal associated with integrated soil moisture that rescales the measured neutron intensity to that which would have been observed in the atmospheric conditions prevailing on the day of sensor calibration. Use of this approach is investigated with in situ observations at two sites characterized by strong seasonality in water vapor where standard meteorological measurements are readily available.

Error estimation for soil moisture measurements with cosmic-ray neutron sensing and implications for rover surveys

2020 ◽  
Author(s):  
Jannis Jakobi ◽  
Johan Alexander Huisman ◽  
Martin Schrön ◽  
Justus Fiedler ◽  
Cosimo Brogi ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Measurement Uncertainty ◽  
Survey Design ◽  
Time Windows ◽  
Inverse Correlation ◽  
Cosmic Ray ◽  
Environmental Water ◽  
Neutron Measurement ◽  
Neutron Intensity ◽  
Computationally Intensive

<p>The cosmic ray neutron (CRN) probe is a non-invasive device to measure soil moisture at the field scale. This instrument relies on the inverse correlation between aboveground epithermal neutron intensity (1eV – 100 keV) and environmental water content. The measurement uncertainty of the neutron detector follows Poisson statistics and thus decreases with decreasing neutron intensity, which corresponds to increasing soil moisture. In order to reduce measurement uncertainty (e.g. < 0.03 m<sup>3</sup>/m<sup>3</sup>), the neutron count rate is often aggregated over large time windows (e.g. 12h or 24h). To enable shorter aggregation intervals, the measurement uncertainty can be reduced either by using more efficient detectors or by using arrays of detectors, as in the case of CRN rover applications. Depending on soil moisture and driving speed, aggregation of neutron counts may also be necessary to obtain sufficiently accurate soil moisture estimates in rover applications. To date, signal aggregation has not been investigated sufficiently with respect to the optimisation of temporal (stationary probes) and spatial (roving applications) resolution. In this work, we present an easy-to-use method for uncertainty quantification of soil moisture observations from CRN sensors based on Gaussian error propagation theory. We have estimated the uncertainty using a third order Taylor expansion and compared the result with a more computationally intensive Monte Carlo approach and found excellent agreement. Furthermore, we used our method to quantify the dependence of soil moisture uncertainty on CRN rover survey design and on selected aggregation time. We anticipate that the new approach helps to quantify cosmic ray neutron measurement uncertainty. In particular, it is anticipated that the strategic planning and evaluation of CRN rover surveys based on uncertainty requirements can be improved considerably.</p>

scholarly journals Can canopy interception and biomass be inferred from cosmic-ray neutron intensity? Results from neutron transport modeling

2016 ◽  
Author(s):  
Mie Andreasen ◽  
Karsten H. Jensen ◽  
Darin Desilets ◽  
Marek Zreda ◽  
Heye Bogena ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Epithermal Neutron ◽  
Neutron Transport ◽  
Forest Biomass ◽  
Cosmic Ray ◽  
Ground Level ◽  
Field Site ◽  
Canopy Interception ◽  
Soil Matrix ◽  
Neutron Intensity

Abstract. Cosmic-ray neutron intensity is inversely correlated to all hydrogen present in the upper decimeters of the subsurface and the first few hectometers of the atmosphere above the ground surface. This method has been used for measuring soil moisture and snow water equivalent, but it may also be used to identify and quantify canopy interception and biomass. We use a neutron transport model with various representations of the forest and different parameters describing the subsurface to match measured profiles and time series of thermal and epithermal neutron intensities at a field site in Denmark. A sensitivity analysis is performed to quantify the effect of forest canopy representation, soil moisture, complexity of soil matrix chemistry, forest litter, soil bulk density, canopy interception and forest biomass on neutron intensity. The results show that forest biomass has a significant influence on the neutron intensity profiles at the examined field site, altering both the shape of the profiles and the ground level thermal-to-epithermal neutron ratio. The ground level thermal-to-epithermal neutron ratio increases significantly with increasing amounts of biomass and minor with canopy interception. Satisfactory agreement is found between measurements and model results at the forest site as well as two nearby sites representing agricultural and heathland ecosystems. The measured ground level thermal-to-epithermal neutron ratios of the three site range from around 0.56 to 0.82. The significantly smaller effect of canopy interception on the ground level thermal-to-epithermal neutron ratio was modeled to range from 0.804 to 0.836 for a forest with a dry and a very wet canopy (4 mm of canopy interception), respectively. At the examined field site the signal of the canopy interception is lower than the measurement uncertainty.

Moisture and humidity dependence of the above-ground cosmic-ray neutron intensity

2020 ◽  
Author(s):  
Jannis Weimar ◽  
Markus Köhli ◽  
Martin Schrön ◽  
Ulrich Schmidt
Keyword(s):  
Monte Carlo ◽  
Soil Moisture ◽  
Neutron Transport ◽  
Cosmic Ray ◽  
Data Sets ◽  
Neutron Intensity ◽  
Alpine Regions ◽  
Neutron Count ◽  
Snow Water ◽  
Humidity Dependence

<p>The novel method of Cosmic-ray neutron sensing (CRNS) allows non-invasive soil moisture measurements at a hectometer scaled footprint. Using this technique one can relate the flux density of albedo neutrons, generated in cosmic-ray induced air showers, to the amount of water within a radius of several hundred meters. In the recent years the understanding of neutron transport by Monte Carlo simulations led to major advancements in precision, which have successfully targeted a manifold of use cases. For example the improvements in the signal interpretation have meanwhile also been applied to the determination of snow water in Alpine regions. Up to now, the conversion of soil moisture to a detectable neutron count rate relies mainly on the equation presented by Desilets and Zreda. While in general a hyperbolic expression can be derived from theoretical considerations, their empiric parameterisation needs to be revised as many groups have found site-specific calibrations, which are simply based on different empirical data sets.</p><p>Investigating the above-ground neutron intensity by a broadly based Monte Carlo simulation campaign revealed a more detailed understanding of different contributions to this signal, especially targeting air humidity corrections. The packages MCNP and URANOS were used to derive a function able to describe the respective dependencies including the effect of different hydrogen pools and the sensor response function. The resulting formula significantly improves the soil-moisture-to-intensity conversion and allows for a more comprehensive instrument data quality, which especially closes the gap between observations of very dry and wet conditions.</p>

scholarly journals The COsmic-ray Soil Moisture Interaction Code (COSMIC) for use in data assimilation

2013 ◽  
Vol 17 (8) ◽  
pp. 3205-3217 ◽  
Author(s):  
J. Shuttleworth ◽  
R. Rosolem ◽  
M. Zreda ◽  
T. Franz
Keyword(s):  
Soil Moisture ◽  
Data Assimilation ◽  
Fast Neutron ◽  
Land Surface ◽  
Soil Depth ◽  
Cosmic Ray ◽  
High Energy ◽  
Fast Neutrons ◽  
Surface Model ◽  
Neutron Intensity

Abstract. Soil moisture status in land surface models (LSMs) can be updated by assimilating cosmic-ray neutron intensity measured in air above the surface. This requires a fast and accurate model to calculate the neutron intensity from the profiles of soil moisture modeled by the LSM. The existing Monte Carlo N-Particle eXtended (MCNPX) model is sufficiently accurate but too slow to be practical in the context of data assimilation. Consequently an alternative and efficient model is needed which can be calibrated accurately to reproduce the calculations made by MCNPX and used to substitute for MCNPX during data assimilation. This paper describes the construction and calibration of such a model, COsmic-ray Soil Moisture Interaction Code (COSMIC), which is simple, physically based and analytic, and which, because it runs at least 50 000 times faster than MCNPX, is appropriate in data assimilation applications. The model includes simple descriptions of (a) degradation of the incoming high-energy neutron flux with soil depth, (b) creation of fast neutrons at each depth in the soil, and (c) scattering of the resulting fast neutrons before they reach the soil surface, all of which processes may have parameterized dependency on the chemistry and moisture content of the soil. The site-to-site variability in the parameters used in COSMIC is explored for 42 sample sites in the COsmic-ray Soil Moisture Observing System (COSMOS), and the comparative performance of COSMIC relative to MCNPX when applied to represent interactions between cosmic-ray neutrons and moist soil is explored. At an example site in Arizona, fast-neutron counts calculated by COSMIC from the average soil moisture profile given by an independent network of point measurements in the COSMOS probe footprint are similar to the fast-neutron intensity measured by the COSMOS probe. It was demonstrated that, when used within a data assimilation framework to assimilate COSMOS probe counts into the Noah land surface model at the Santa Rita Experimental Range field site, the calibrated COSMIC model provided an effective mechanism for translating model-calculated soil moisture profiles into aboveground fast-neutron count when applied with two radically different approaches used to remove the bias between data and model.

scholarly journals A universal calibration function for determination of soil moisture with cosmic-ray neutrons

2013 ◽  
Vol 17 (2) ◽  
pp. 453-460 ◽  
Author(s):  
T. E. Franz ◽  
M. Zreda ◽  
R. Rosolem ◽  
T. P. A. Ferre
Keyword(s):  
Soil Moisture ◽  
Pore Water ◽  
Water Distribution ◽  
Neutron Transport ◽  
Cosmic Ray ◽  
The Other ◽  
Calibration Function ◽  
Neutron Intensity ◽  
Intensity Measurements ◽  
Universal Calibration

Abstract. A cosmic-ray soil moisture probe is usually calibrated locally using soil samples collected within its support volume. But such calibration may be difficult or impractical, for example when soil contains stones, in presence of bedrock outcrops, in urban environments, or when the probe is used as a rover. Here we use the neutron transport code MCNPx with observed soil chemistries and pore water distribution to derive a universal calibration function that can be used in such environments. Reasonable estimates of pore water content can be made from neutron intensity measurements and by using measurements of the other hydrogen pools (water vapor, soil lattice water, soil organic carbon, and biomass). Comparisons with independent soil moisture measurements at one cosmic-ray probe site and, separately, at 35 sites, show that the universal calibration function explains more than 79% of the total variability within each dataset, permitting accurate isolation of the soil moisture signal from the measured neutron intensity signal. In addition the framework allows for any of the other hydrogen pools to be separated from the neutron intensity measurements, which may be useful for estimating changes in biomass, biomass water, or exchangeable water in complex environments.

scholarly journals The COsmic-ray Soil Moisture Interaction Code (COSMIC) for use in data assimilation

2013 ◽  
Vol 10 (1) ◽  
pp. 1097-1125 ◽  
Author(s):  
J. Shuttleworth ◽  
R. Rosolem ◽  
M. Zreda ◽  
T. Franz
Keyword(s):  
Soil Moisture ◽  
Data Assimilation ◽  
Fast Neutron ◽  
Land Surface ◽  
Soil Depth ◽  
Cosmic Ray ◽  
High Energy ◽  
Fast Neutrons ◽  
Surface Model ◽  
Neutron Intensity

Abstract. Soil moisture status in land surface models (LSMs) can be updated by assimilating cosmic-ray neutron intensity measured in air above the surface. This requires a fast and accurate model to calculate the neutron intensity from the profiles of soil moisture modeled by the LSM. The existing Monte Carlo N-Particle eXtended (MCNPX) model is sufficiently accurate but too slow to be practical in the context of data assimilation. Consequently an alternative and efficient model is needed which can be calibrated accurately to reproduce the calculations made by MCNPX and used to substitute for MCNPX during data assimilation. This paper describes the construction and calibration of such a model, COSMIC, which is simple, physically-based and analytic and, because it runs at least 50 000 times faster than MCNPX, is appropriate in data assimilation applications. The model includes simple descriptions of (a) degradation of the incoming high energy neutron flux with soil depth, (b) creation of fast neutrons at each depth in the soil, and (c) scattering of the resulting fast neutrons before they reach the soil surface, all of which processes may have parameterized dependency on the chemistry and moisture content of the soil. The site-to-site variability in the parameters used in COSMIC is explored for 42 sample sites in the COsmic-ray Soil Moisture Observing System (COSMOS), and the comparative performance of COSMIC relative to MCNPX when applied to represent interactions between cosmic-ray neutrons and moist soilis explored. At an example site in Arizona, fast neutron counts calculated by COSMIC from the average soil moisture profile given by an independent network of point measurements in the COSMOS probe footprint are similar to the fast neutron intensity measured by the COSMOS probe. Moreover at this site application of data assimilation using COSMIC to update the Noah Land Surface Model constrains the modeled soil moisture such that it agrees with the values given by the independent network of point measurements, thus confirming that COSMIC can be used as a robust forward operator in data assimilation of cosmic-ray soil moisture measurements.

scholarly journals Cosmic-ray neutron transport at a forest field site: the sensitivity to various environmental conditions with focus on biomass and canopy interception

2017 ◽  
Vol 21 (4) ◽  
pp. 1875-1894 ◽  
Author(s):  
Mie Andreasen ◽  
Karsten H. Jensen ◽  
Darin Desilets ◽  
Marek Zreda ◽  
Heye R. Bogena ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Epithermal Neutron ◽  
Neutron Transport ◽  
Estimation Method ◽  
Cosmic Ray ◽  
Ground Level ◽  
Field Site ◽  
Canopy Interception ◽  
Neutron Intensity ◽  
Moisture Estimation

Abstract. Cosmic-ray neutron intensity is inversely correlated to all hydrogen present in the upper decimeters of the subsurface and the first few hectometers of the atmosphere above the ground surface. This correlation forms the base of the cosmic-ray neutron soil moisture estimation method. The method is, however, complicated by the fact that several hydrogen pools other than soil moisture affect the neutron intensity. In order to improve the cosmic-ray neutron soil moisture estimation method and explore the potential for additional applications, knowledge about the environmental effect on cosmic-ray neutron intensity is essential (e.g., the effect of vegetation, litter layer and soil type). In this study the environmental effect is examined by performing a sensitivity analysis using neutron transport modeling. We use a neutron transport model with various representations of the forest and different parameters describing the subsurface to match measured height profiles and time series of thermal and epithermal neutron intensities at a field site in Denmark. Overall, modeled thermal and epithermal neutron intensities are in satisfactory agreement with measurements; however, the choice of forest canopy conceptualization is found to be significant. Modeling results show that the effect of canopy interception, soil chemistry and dry bulk density of litter and mineral soil on neutron intensity is small. On the other hand, the neutron intensity decreases significantly with added litter-layer thickness, especially for epithermal neutron energies. Forest biomass also has a significant influence on the neutron intensity height profiles at the examined field site, altering both the shape of the profiles and the ground-level thermal-to-epithermal neutron ratio. This ratio increases with increasing amounts of biomass, and was confirmed by measurements from three sites representing agricultural, heathland and forest land cover. A much smaller effect of canopy interception on the ground-level thermal-to-epithermal neutron ratio was modeled. Overall, the results suggest a potential to use ground-level thermal-to-epithermal neutron ratios to discriminate the effect of different hydrogen contributions on the neutron signal.

scholarly journals Profiling of atmospheric water vapor with MIR and LASE

2002 ◽  
Vol 40 (6) ◽  
pp. 1211-1219 ◽  
Author(s):  
J.R. Wang ◽  
P. Racette ◽  
M.E. Triesky ◽  
E.V. Browell ◽  
S. Ismail ◽  
...  
Keyword(s):  
Water Vapor ◽  
Atmospheric Water Vapor ◽  
Atmospheric Water
Sign in / Sign up

Export Citation Format

Share Document