Accuracy of the cosmic-ray soil water content probe in humid forest ecosystems: The worst case scenario

Bogena, Heye; Huisman, Johan Alexander; Baatz, Roland; Franssen, Harrie‐Jan Hendricks; Vereecken, Harry

doi:10.1002/wrcr.20463

Cited by 193 publications

(285 citation statements)

References 33 publications

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“…Soil moisture is a state variable in the water balance equations of many hydrological, meteorological, and agricultural models; thus, accurate observations of root zone soil moisture over large spatial extents are indispensable for model validation (Grayson and Western, 1998), and for run-time assimilation (e.g. Brocca et al, 2010a). The required spatial scale greatly depends on the application.…”

Section: Introductionmentioning

confidence: 99%

Estimating field-scale root zone soil moisture using the cosmic-ray neutron probe

Peterson

Helgason

Ireson

2016

Hydrol. Earth Syst. Sci.

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Abstract. Many practical hydrological, meteorological, and agricultural management problems require estimates of soil moisture with an areal footprint equivalent to field scale, integrated over the entire root zone. The cosmic-ray neutron probe is a promising instrument to provide field-scale areal coverage, but these observations are shallow and require depth-scaling in order to be considered representative of the entire root zone. A study to identify appropriate depthscaling techniques was conducted at a grazing pasture site in central Saskatchewan, Canada over a 2-year period. Areaaveraged soil moisture was assessed using a cosmic-ray neutron probe. Root zone soil moisture was measured at 21 locations within the 500 m × 500 m study area, using a downhole neutron probe. The cosmic-ray neutron probe was found to provide accurate estimates of field-scale surface soil moisture, but measurements represented less than 40 % of the seasonal change in root zone storage due to its shallow measurement depth. The root zone estimation methods evaluated were: (a) the coupling of the cosmic-ray neutron probe with a time-stable neutron probe monitoring location, (b) coupling the cosmic-ray neutron probe with a representative landscape unit monitoring approach, and (c) convolution of the cosmicray neutron probe measurements with the exponential filter. The time stability method provided the best estimate of root zone soil moisture (RMSE = 0.005 cm 3 cm −3 ), followed by the exponential filter (RMSE = 0.014 cm 3 cm −3 ). The landscape unit approach, which required no calibration, had a negative bias but estimated the cumulative change in storage reasonably. The feasibility of applying these methods to field sites without existing instrumentation is discussed. Based upon its observed performance and its minimal data requirements, it is concluded that the exponential filter method has the most potential for estimating root zone soil moisture from cosmic-ray neutron probe data.

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Section: Introductionmentioning

confidence: 99%

Estimating field-scale root zone soil moisture using the cosmic-ray neutron probe

Peterson

Helgason

Ireson

2016

Hydrol. Earth Syst. Sci.

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“…The analysis and correction of the influences of atmospheric pressure, water vapor, solar activity and aboveground biomass on the neutrons have been studied (Desilets and Zreda, 2001;Moraal et al, 2005;Rosolem et al, 2013;Coopersmith et al, 2014;McJannet et al, 2014;Baatz et al, 2015) and can improve the accuracy of the CRNS. These studies have built the foundation for the application of the CRNS method (Rivera villarreyes et al, 2011;Bogena et al, 2013;Han et al, 2014;Wang et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Application of cosmic-ray neutron sensing to monitor soil water content in an alpine meadow ecosystem on the northern Tibetan Plateau

Zhu

Shao

Zeng

et al. 2016

Journal of Hydrology

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Keywords: CRNS Soil moisture Alpine meadow Tibetan Plateau s u m m a r y Cosmic-ray neutron sensing (CRNS) is a new method for continuously monitoring mean soil water content (SWC) on a hectometer scale. To evaluate the application and accuracy of the method for SWC observation in an alpine meadow ecosystem (AME), we installed the CRNS in a flat meadow near the Naqu prefecture on the northern Tibetan Plateau. We collecting soil samples and applying the system by the oven-drying method. A weather station was also installed near the CRNS for monitoring basic meteorological variables and the soil temperature and water content at various depths. Three Em-50 instruments for monitoring SWC and soil temperature were buried in three sub-quadrats northwest, northeast and southeast of the CRNS at distances of 460, 370 and 373 m, respectively, to observe the variation of SWC at the various depths. The footprint of the CRNS for SWC observation in the meadow was about 580 m, and the mean measuring depth was about 31 cm according to the general calculation equations. The reference neutron flux for dry soil (N 0 ) had a mean and coefficient of variation of 8686 and 3%, respectively, and remained substantially invariant throughout the measuring period. The five SWCs from the independent field samples almost passed through the SWC trend of the CRNS, the root mean square error (RMSE) was 0.011 m 3 m À3 for the CRNS and oven-drying method. The time series of SWC measured by the CRNS agreed well with the mean SWC series to a depth of 20 cm measured by the weather station. The trend of SWC measured by the Em-50s generally agreed with the trend of SWC measured by the CRNS, but some values and variations of SWC differed between the Em-50s and CRNS data. Because of the good agreement between the CRNS and independent field samples, we suspect that this disagreement is due to an insufficient representativeness of point observations and the distances of the points from the CRNS. The diurnal variation of hourly SWC from the CRNS was sinusoidal during a dry period, peaking at 11:00 and was minimum at 18:00 (Beijing time), with a range of 1%. Overall, the CRNS measured SWC in the AME with an acceptable accuracy, providing a scientific basis for the promotion and application of the CRNS in high, cold ecosystems.

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“…Corrections were applied as by Zreda et al (2012). Water vapour corrections were applied with respect to dry air (Bogena et al, 2013). The quality control approach used for the PS analysis was also applied to CRNS neutron count data series to remove unrealistic points.…”

Section: Calibration and Validation Data: Ps Crns And Eddy-covarianmentioning

confidence: 99%

Land surface model performance using cosmic-ray and point-scale soil moisture measurements for calibration

Iwema

Rosolem

Rahman

et al. 2017

Hydrol. Earth Syst. Sci.

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Abstract. At very high resolution scale (i.e. grid cells of 1 km 2 ), land surface model parameters can be calibrated with eddy-covariance flux data and point-scale soil moisture data. However, measurement scales of eddy-covariance and point-scale data differ substantially. In our study, we investigated the impact of reducing the scale mismatch between surface energy flux and soil moisture observations by replacing point-scale soil moisture data with observations derived from Cosmic-Ray Neutron Sensors (CRNSs) made at larger spatial scales. Five soil and evapotranspiration parameters of the Joint UK Land Environment Simulator (JULES) were calibrated against point-scale and Cosmic-Ray Neutron Sensor soil moisture data separately. We calibrated the model for 12 sites in the USA representing a range of climatic, soil, and vegetation conditions. The improvement in latent heat flux estimation for the two calibration solutions was assessed by comparison to eddy-covariance flux data and to JULES simulations with default parameter values. Calibrations against the two soil moisture products alone did show an advantage for the cosmic-ray technique. However, further analyses of two-objective calibrations with soil moisture and latent heat flux showed no substantial differences between both calibration strategies. This was mainly caused by the limited effect of calibrating soil parameters on soil moisture dynamics and surface energy fluxes. Other factors that played a role were limited spatial variability in surface fluxes implied by soil moisture spatio-temporal stability, and data quality issues.

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Accuracy of the cosmic-ray soil water content probe in humid forest ecosystems: The worst case scenario

Cited by 193 publications

References 33 publications

Estimating field-scale root zone soil moisture using the cosmic-ray neutron probe

Estimating field-scale root zone soil moisture using the cosmic-ray neutron probe

Application of cosmic-ray neutron sensing to monitor soil water content in an alpine meadow ecosystem on the northern Tibetan Plateau

Land surface model performance using cosmic-ray and point-scale soil moisture measurements for calibration

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