scholarly journals Soil hydraulic material properties and subsurface architecture from time-lapse GPR

2017 ◽  
Author(s):  
Stefan Jaumann ◽  
Kurt Roth
Keyword(s):  
Soil Water ◽  
Material Properties ◽  
Simulated Annealing Algorithm ◽  
Water Movement ◽  
Ground Truth ◽  
Time Domain Reflectometry ◽  
Richards Equation ◽  
Ground Truth Data ◽  
Marquardt Algorithm ◽  
Soil Hydraulic

Abstract. Quantitative knowledge of effective soil hydraulic material properties is essential to predict soil water movement. Ground-penetrating radar (GPR) is a non-invasive and non-destructive geophysical measurement method to monitor the hydraulic processes precisely. Previous studies showed that the GPR signal from a fluctuating groundwater table is sensitive to the soil water characteristic and the hydraulic conductivity function. In this work, we show that this signal is suitable to accurately estimate the subsurface architecture and the associated effective soil hydraulic material properties with inversion methods. Therefore, we parameterize the subsurface architecture, solve the Richards equation, convert the resulting water content to relative permittivity with the complex reflective index model (CRIM), and solve Maxwell's equations numerically. In order to analyze the GPR signal, we implemented a new heuristic event detection and association algorithm. Using events instead of the full wave regularizes the inversion as it allows to focus on the relevant measurement signal. Starting from an ensemble of Latin hypercube drawn initial parameter sets, we sequentially couple the simulated annealing algorithm with the Levenberg–Marquardt algorithm. We apply the method to synthetic as well as measured data from the ASSESS test site and show that the method yields accurate estimates for the soil hydraulic material properties as well as for the subsurface architecture by comparing the results to references derived from time domain reflectometry (TDR) and subsurface architecture ground truth data.

scholarly journals Soil hydraulic material properties and layered architecture from time-lapse GPR

2018 ◽  
Vol 22 (4) ◽  
pp. 2551-2573 ◽  
Author(s):  
Stefan Jaumann ◽  
Kurt Roth
Keyword(s):  
Soil Water ◽  
Material Properties ◽  
Simulated Annealing Algorithm ◽  
Water Movement ◽  
Time Domain Reflectometry ◽  
Groundwater Table ◽  
Richards Equation ◽  
Ground Truth Data ◽  
Marquardt Algorithm ◽  
Soil Hydraulic

Abstract. Quantitative knowledge of the subsurface material distribution and its effective soil hydraulic material properties is essential to predict soil water movement. Ground-penetrating radar (GPR) is a noninvasive and nondestructive geophysical measurement method that is suitable to monitor hydraulic processes. Previous studies showed that the GPR signal from a fluctuating groundwater table is sensitive to the soil water characteristic and the hydraulic conductivity function. In this work, we show that the GPR signal originating from both the subsurface architecture and the fluctuating groundwater table is suitable to estimate the position of layers within the subsurface architecture together with the associated effective soil hydraulic material properties with inversion methods. To that end, we parameterize the subsurface architecture, solve the Richards equation, convert the resulting water content to relative permittivity with the complex refractive index model (CRIM), and solve Maxwell's equations numerically. In order to analyze the GPR signal, we implemented a new heuristic algorithm that detects relevant signals in the radargram (events) and extracts the corresponding signal travel time and amplitude. This algorithm is applied to simulated as well as measured radargrams and the detected events are associated automatically. Using events instead of the full wave regularizes the inversion focussing on the relevant measurement signal. For optimization, we use a global–local approach with preconditioning. Starting from an ensemble of initial parameter sets drawn with a Latin hypercube algorithm, we sequentially couple a simulated annealing algorithm with a Levenberg–Marquardt algorithm. The method is applied to synthetic as well as measured data from the ASSESS test site. We show that the method yields reasonable estimates for the position of the layers as well as for the soil hydraulic material properties by comparing the results to references derived from ground truth data as well as from time domain reflectometry (TDR).

Modelling water uptake by a mature apple tree

Soil Research ◽  
2003 ◽  
Vol 41 (3) ◽  
pp. 365 ◽  
Author(s):  
S. R. Green ◽  
I. Vogeler ◽  
B. E. Clothier ◽  
T. M. Mills ◽  
C. van den Dijssel
Keyword(s):  
Experimental Data ◽  
Water Content ◽  
Soil Water ◽  
Water Uptake ◽  
Apple Tree ◽  
Water Movement ◽  
Root Zone ◽  
Time Domain Reflectometry ◽  
Richards Equation ◽  
Mature Apple

We report the results from a field experiment in which we examined the spatial and temporal patterns of water uptake by a mature apple tree (Malus domestica Borkh., 'Splendour') in an orchard. Time domain reflectometry was used to measure changes in the soil's volumetric water content, and heat-pulse was used to monitor locally the rates of sap flow in the trunk and roots of the tree. The tree's distribution of root-length density and supporting data to characterise the soil's hydraulic properties were determined for the purpose of modelling soil water movement in the root-zone under an apple tree. Experimental data are compared against the output from a numerical model of the soil water balance that uses Richards' equation for water flow, and uses a distributed macroscopic sink term for root uptake. In general, there was a very good agreement between the measured and modelled results. The apple trees consumed some 70 L of water per day during the middle of summer. The daily water use declined to about 20 L per day with the onset of autumn, coinciding with a reduced evaporative demand and an increasing number of rain days. Water movement in the root-zone soil was dominated by the water uptake via surface roots. Large changes in soil water content were also associated with each irrigation event. Our experimental data support the contention that more frequent irrigation in smaller doses will result in less water percolating through the root-zone. Such an irrigation strategy should make more efficient use of water by minimising the leaching losses. It will also be helpful for environmental protection by reducing the percolation losses of water and solute beyond the grasp of the roots.

scholarly journals Calibrating electromagnetic induction conductivities with time-domain reflectometry measurements

2017 ◽  
Author(s):  
Giovanna Dragonetti ◽  
Alessandro Comegna ◽  
Ali Ajeel ◽  
Gian Piero Deidda ◽  
Nicola Lamaddalena ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Time Domain ◽  
Electromagnetic Induction ◽  
Root Zone ◽  
Ground Truth ◽  
Time Domain Reflectometry ◽  
Data Series ◽  
Actual Distribution ◽  
Ground Truth Data ◽  
Soil Measurements

Abstract. This paper deals with the issue of monitoring the horizontal and vertical distribution of bulk electrical conductivity, σb, in the soil root zone by using Electromagnetic Induction (EMI) sensors under different water and salinity conditions. In order to deduce the actual distribution of depth-specific σb from EMI depth-weighted apparent electrical conductivity (ECa) measurements, we inverted the signal by using a regularized 1D inversion procedure designed to manage nonlinear multiple EMI-depth responses. The inversion technique is based on the coupling of the damped Gauss-Newton method with truncated generalized singular value decomposition (TGSVD). The ill-posedness of the EMI data inversion is addressed by using a sharp stabilizer term in the objective function. This specific stabilizer promotes the reconstruction of blocky targets, thereby contributing to enhance the spatial resolution of the EMI reconstruction. Time-Domain Reflectometry (TDR) data are used as ground-truth data for calibration of the inversion results. An experimental field was divided into four transects 30 m long and 2.8 m wide, cultivated with green bean and irrigated with water at two different salinity levels and using two different irrigation volumes, to induce different salinity and water contents within the soil profile. For each transect, 26 regularly spaced monitoring sites (1 m apart) were selected for soil measurements using a Geonics EM-38 and a Tektronix Reflectometer. Despite the original discrepancies in the EMI and TDR data, we found a significantly high correlation of the means and standard deviations of the two data series, especially after filtering the TDR data. Based on these findings, the paper introduces a novel methodology to calibrate EMI-based electrical conductivity via TDR direct measurements by simply using the statistics of the two data series.

scholarly journals Kalman filters for assimilating near-surface observations into the Richards equation – Part 2: A dual filter approach for simultaneous retrieval of states and parameters

2014 ◽  
Vol 18 (7) ◽  
pp. 2521-2541 ◽  
Author(s):  
H. Medina ◽  
N. Romano ◽  
G. B. Chirico
Keyword(s):  
Time Series ◽  
Kalman Filter ◽  
Closed Form ◽  
Soil Water ◽  
Unscented Kalman Filter ◽  
Richards Equation ◽  
Near Surface ◽  
Form Model ◽  
Soil Hydraulic ◽  
Synthetic Time Series

Abstract. This study presents a dual Kalman filter (DSUKF – dual standard-unscented Kalman filter) for retrieving states and parameters controlling the soil water dynamics in a homogeneous soil column, by assimilating near-surface state observations. The DSUKF couples a standard Kalman filter for retrieving the states of a linear solver of the Richards equation, and an unscented Kalman filter for retrieving the parameters of the soil hydraulic functions, which are defined according to the van Genuchten–Mualem closed-form model. The accuracy and the computational expense of the DSUKF are compared with those of the dual ensemble Kalman filter (DEnKF) implemented with a nonlinear solver of the Richards equation. Both the DSUKF and the DEnKF are applied with two alternative state-space formulations of the Richards equation, respectively differentiated by the type of variable employed for representing the states: either the soil water content (θ) or the soil water matric pressure head (h). The comparison analyses are conducted with reference to synthetic time series of the true states, noise corrupted observations, and synthetic time series of the meteorological forcing. The performance of the retrieval algorithms are examined accounting for the effects exerted on the output by the input parameters, the observation depth and assimilation frequency, as well as by the relationship between retrieved states and assimilated variables. The uncertainty of the states retrieved with DSUKF is considerably reduced, for any initial wrong parameterization, with similar accuracy but less computational effort than the DEnKF, when this is implemented with ensembles of 25 members. For ensemble sizes of the same order of those involved in the DSUKF, the DEnKF fails to provide reliable posterior estimates of states and parameters. The retrieval performance of the soil hydraulic parameters is strongly affected by several factors, such as the initial guess of the unknown parameters, the wet or dry range of the retrieved states, the boundary conditions, as well as the form (h-based or θ-based) of the state-space formulation. Several analyses are reported to show that the identifiability of the saturated hydraulic conductivity is hindered by the strong correlation with other parameters of the soil hydraulic functions defined according to the van Genuchten–Mualem closed-form model.

scholarly journals Direct measurement of the soil water retention curve using X-ray absorption

2004 ◽  
Vol 8 (1) ◽  
pp. 2-7 ◽  
Author(s):  
A. Bayer ◽  
H.-J. Vogel ◽  
K. Roth
Keyword(s):  
Soil Water ◽  
Hydraulic Properties ◽  
Capillary Rise ◽  
Water Dynamics ◽  
Richards Equation ◽  
Water Retention Curve ◽  
Soil Hydraulic Properties ◽  
X Ray ◽  
Soil Hydraulic ◽  
X Ray Absorption

Abstract. X-ray absorption measurements have been explored as a fast experimental approach to determine soil hydraulic properties and to study rapid dynamic processes. As examples, the pressure-saturation relation θ(Ψ) for a uniform sand column has been considered as has capillary rise in an initially dry sintered glass column. The θ(Ψ)-relation is in reasonable agreement with that obtained by inverting a traditional multi-step outflow experiment. Monitoring the initial phase of capillary rise reveals behaviour that deviates qualitatively from the single-phase, local-equilibrium regime described by Richards’ equation. Keywords: X-ray absorption, soil hydraulic properties, soil water dynamics, Richards’ equation

scholarly journals Soil moisture monitoring in the Toce valley (Italy)

2003 ◽  
Vol 7 (6) ◽  
pp. 890-902 ◽  
Author(s):  
M. Menziani ◽  
S. Pugnaghi ◽  
S. Vincenzi ◽  
R. Santangelo
Keyword(s):  
Mass Balance ◽  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Time Domain ◽  
Heavy Precipitation ◽  
Time Domain Reflectometry ◽  
Balance Method ◽  
Richards Equation ◽  
Mass Balance Method

Abstract. In the framework of the Mesoscale Alpine Programme (MAP), soil water content profiles were collected at a point station in the Toce Valley (Lago Maggiore MAP Target Area). The data are for the first 70 cm depth of soil for the period April–November, 1999. All measurements were made by a Time Domain Reflectometry device. The time variation of the water stored in a column of soil was estimated by a mass balance method. Evaporation was estimated from the data collected in the summer period. Likewise, by applying the mass balance method to the data collected during and after heavy precipitation events, the water infiltrated into the soil was also estimated. A qualitative evaluation of ponding and/or runoff as the difference between the precipitated and the drained water was obtained under suitable assumptions. Furthermore, the time evolution of the soil water content profile was studied by solving the Richards equation both analytically and numerically for two particular cases: the driest period and a period following a heavy precipitation event. Finally, during the MAP Special Observing Period, two intensive campaigns were performed, together with measurements using an airborne passive microwave radiometer, to assess the spatial distribution of the surface (0–30 cm depth) soil water content in fields with different physical and agricultural characteristics. Keywords: soil water content, Time Domain Reflectometry, TDR temperature-dependence, evaporation, infiltration, runoff, linearised Richards equation.

scholarly journals Modeling Soil Water Redistribution under Gravity Irrigation with the Richards Equation

Mathematics ◽  
2020 ◽  
Vol 8 (9) ◽  
pp. 1581 ◽  
Author(s):  
Sebastián Fuentes ◽  
Josué Trejo-Alonso ◽  
Antonio Quevedo ◽  
Carlos Fuentes ◽  
Carlos Chávez
Keyword(s):  
Finite Difference ◽  
Numerical Solution ◽  
Soil Water ◽  
Water Movement ◽  
Soil Mechanics ◽  
Water Infiltration ◽  
Richards Equation ◽  
Water Redistribution ◽  
Irrigation Drainage ◽  
Transfer Problems

Soil water movement is important in fields such as soil mechanics, irrigation, drainage, hydrology, and agriculture. The Richards equation describes the flow of water in an unsaturated porous medium, and analytical solutions exist only for simplified cases. However, numerous practical situations require a numerical solution (1D, 2D, or 3D) depending on the complexity of the studied problem. In this paper, numerical solution of the equation describing water infiltration into soil using the finite difference method is studied. The finite difference solution is made via iterative schemes of local balance, including explicit, implicit, and intermediate methods; as a special case, the Laasonen method is shown. The found solution is applied to water transfer problems during and after gravity irrigation to observe phenomena of infiltration, evaporation, transpiration, and percolation.

scholarly journals Numerical Evaluation of Fractional Vertical Soil Water Flow Equations

Water ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 511
Author(s):  
Ali Ercan ◽  
M. Levent Kavvas
Keyword(s):  
Porous Media ◽  
Soil Water ◽  
Water Flow ◽  
Water Movement ◽  
Least Square ◽  
Flow In Porous Media ◽  
Fickian Diffusion ◽  
Richards Equation ◽  
Governing Equations ◽  
Soil Water Flow

Significant deviations from standard Boltzmann scaling, which corresponds to normal or Fickian diffusion, have been observed in the literature for water movement in porous media. However, as demonstrated by various researchers, the widely used conventional Richards equation cannot mimic anomalous diffusion and ignores the features of natural soils which are heterogeneous. Within this framework, governing equations of transient water flow in porous media in fractional time and multi-dimensional fractional soil space in anisotropic media were recently introduced by the authors by coupling Brooks–Corey constitutive relationships with the fractional continuity and motion equations. In this study, instead of utilizing Brooks–Corey relationships, empirical expressions, obtained by least square fits through hydraulic measurements, were utilized to show the suitability of the proposed fractional approach with other constitutive hydraulic relations in the literature. Next, a finite difference numerical method was proposed to solve the fractional governing equations. The applicability of the proposed fractional governing equations was investigated numerically in comparison to their conventional counterparts. In practice, cumulative infiltration values are observed to deviate from conventional infiltration approximation, or the wetting front through time may not be consistent with the traditional estimates of Richards equation. In such cases, fractional governing equations may be a better alternative for mimicking the physical process as they can capture sub-, super-, and normal-diffusive soil water flow processes during infiltration.

scholarly journals Effect of unrepresented model errors on estimated soil hydraulic material properties

2017 ◽  
Vol 21 (9) ◽  
pp. 4301-4322 ◽  
Author(s):  
Stefan Jaumann ◽  
Kurt Roth
Keyword(s):  
Material Properties ◽  
Measurement Data ◽  
Absolute Error ◽  
Time Domain Reflectometry ◽  
Model Complexity ◽  
Small Scale ◽  
Model Errors ◽  
Potential Measurement ◽  
Scale Heterogeneity ◽  
Soil Hydraulic

Abstract. Unrepresented model errors influence the estimation of effective soil hydraulic material properties. As the required model complexity for a consistent description of the measurement data is application dependent and unknown a priori, we implemented a structural error analysis based on the inversion of increasingly complex models. We show that the method can indicate unrepresented model errors and quantify their effects on the resulting material properties. To this end, a complicated 2-D subsurface architecture (ASSESS) was forced with a fluctuating groundwater table while time domain reflectometry (TDR) and hydraulic potential measurement devices monitored the hydraulic state. In this work, we analyze the quantitative effect of unrepresented (i) sensor position uncertainty, (ii) small scale-heterogeneity, and (iii) 2-D flow phenomena on estimated soil hydraulic material properties with a 1-D and a 2-D study. The results of these studies demonstrate three main points: (i) the fewer sensors are available per material, the larger is the effect of unrepresented model errors on the resulting material properties. (ii) The 1-D study yields biased parameters due to unrepresented lateral flow. (iii) Representing and estimating sensor positions as well as small-scale heterogeneity decreased the mean absolute error of the volumetric water content data by more than a factor of 2 to 0. 004.

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