Effects of Near Surface Soil Moisture Profiles During Evaporation on Far‐Field Ground‐Penetrating Radar Data: A Numerical Study

We investigated the eff ects of a drying front that emerges below an evaporating soil surface on the far-field ground-penetrating radar (GPR) data. First, we performed an analysis of the width of the drying front in soils with 12 diff erent textures by using an analytical model. Then, we numerically simulated vertical soil moisture profiles that develop during evaporation for the soil textures. We performed the simulations using a Richards flow model that considers only liquid water flow and a model that considers coupled water, vapor, and heat flows. The GPR signals were then generated from the simulated soil water content profiles taking into account the frequency dependency of apparent electrical conductivity and dielectric permitivity. The analytical approach indicated that the width of the drying front at the end of Stage I of the evaporation was larger in silty soils than in other soil textures and smaller in sandy soils. We also demonstrated that the analytical estimate of the width of the drying front can be considered as a proxy for the impact that a drying front could have on far-field GPR data. The numerical simulations led to the conclusion that vapor transport in soil resulted in S-shaped soil moisture profiles, which clearly influenced the GPR data. As a result, vapor flow needs to be considered when GPR data are interpreted in a coupled inversion approach. Moreover, the impact of vapor flow on the GPR data was larger for silty than for sandy soils. These effects on the GPR data provide promising perspectives regarding the use of radars for evaporation monitoring.

[1]  Bridget R. Scanlon,et al.  Numerical Analysis of Coupled Water, Vapor, and Heat Transport in the Vadose Zone , 2005 .

[2]  D. Or,et al.  Pore scale mechanisms for enhanced vapor transport through partially saturated porous media , 2012 .

[3]  S. Dautrebande,et al.  A method of measuring soil moisture by time-domain reflectometry , 1986 .

[4]  L. A. Richards.  Capillary conduction of liquids through porous mediums , 1931 .

[5]  A. Shutko,et al.  Mixture Formulas Applied in Estimation of Dielectric and Radiative Characteristics of Soils and Grounds at Microwave Frequencies , 1982, IEEE Transactions on Geoscience and Remote Sensing.

[6]  Y. Mualem.  A New Model for Predicting the Hydraulic Conductivity , 1976 .

[7]  Marnik Vanclooster,et al.  Closed loop GPR data inversion for soil hydraulic and electric property determination , 2006 .

[8]  Brian Borchers,et al.  Modeling transient temperature distributions around landmines in homogenous bare soils , 2001, SPIE Defense + Commercial Sensing.

[9]  S. Wuest,et al.  Vapor Transport vs. Seed–Soil Contact in Wheat Germination , 1999 .

[10]  Craig H. Benson,et al.  Water Balance Modeling of Earthen Final Covers , 1997 .

[11]  T. Baumgartl,et al.  Applying HYDRUS to Flow in a Sodic Clay Soil with Solution Composition–Dependent Hydraulic Conductivity , 2012 .

[12]  Y. Rubin,et al.  Soil moisture content estimation using ground-penetrating radar reflection data , 2005 .

[13]  Susan S. Hubbard,et al.  Ground‐penetrating‐radar‐assisted saturation and permeability estimation in bimodal systems , 1997 .

[14]  Van Genuchten,et al.  A closed-form equation for predicting the hydraulic conductivity of unsaturated soils , 1980 .

[15]  Shmulik P. Friedman,et al.  A method for measuring the solid particle permittivity or electrical conductivity of rocks, sediments, and granular materials , 2003 .

[16]  T. Miyamoto,et al.  Effects of Liquid-phase Electrical Conductivity, Water Content, and Surface Conductivity on Bulk Soil Electrical Conductivity1 , 1976 .

[17]  Miroslav Šejna,et al.  Development and Applications of the HYDRUS and STANMOD Software Packages and Related Codes , 2008 .

[18]  Evert Slob,et al.  Joint full-waveform analysis of off-ground zero-offset ground penetrating radar and electromagnetic induction synthetic data for estimating soil electrical properties , 2010 .

[19]  Marnik Vanclooster,et al.  Analysis of air‐launched ground‐penetrating radar techniques to measure the soil surface water content , 2006 .

[20]  H. Vereecken.  Estimating the unsaturated hydraulic conductivity from theoretical models using simple soil properties , 1995 .

[21]  Dani Or,et al.  Near-Surface Soil Water Content Measurements Using Horn Antenna Radar: Methodology and Overview , 2003 .

[22]  Dani Or,et al.  Effects of Maxwell‐Wagner polarization on soil complex dielectric permittivity under variable temperature and electrical conductivity , 2006 .

[23]  Evert Slob,et al.  Remote Estimation of the Hydraulic Properties of a Sand Using Full‐Waveform Integrated Hydrogeophysical Inversion of Time‐Lapse, Off‐Ground GPR Data , 2009 .

[24]  Lutz Weihermüller,et al.  Estimation of Soil Hydraulic Parameters in the Field by Integrated Hydrogeophysical Inversion of Time‐Lapse Ground‐Penetrating Radar Data , 2012 .

[25]  Evert Slob,et al.  Fast evaluation of zero‐offset Green's function for layered media with application to ground‐penetrating radar , 2007 .

[26]  Evert C. Slob,et al.  Analysis of Horn Antenna Transfer Functions and Phase-Center Position for Modeling Off-Ground GPR , 2011, IEEE Transactions on Geoscience and Remote Sensing.

[27]  C. Swift,et al.  An improved model for the dielectric constant of sea water at microwave frequencies , 1977 .

[28]  Y. Rubin,et al.  Hydrogeological parameter estimation using geophysical data: a review of selected techniques , 2000 .

[29]  M. Vanclooster,et al.  Uniqueness and stability analysis of hydrogeophysical inversion for time‐lapse ground‐penetrating radar estimates of shallow soil hydraulic properties , 2008 .

[30]  R. Carsel,et al.  Developing joint probability distributions of soil water retention characteristics , 1988 .

[31]  Yoram Rubin,et al.  Forward modeling of ground‐penetrating radar data using digitized outcrop images and multiple scenarios of water saturation , 2001 .

[32]  J. Morel,et al.  Predictability of the Evolution of the Soil Structure using Water Flow Modeling for a Constructed Technosol , 2012 .

[33]  Andrea Benedetto,et al.  Water content evaluation in unsaturated soil using GPR signal analysis in the frequency domain , 2010 .

[34]  Marnik Vanclooster,et al.  Electromagnetic Inversion of GPR Signals and Subsequent Hydrodynamic Inversion to Estimate Effective Vadose Zone Hydraulic Properties , 2004 .

[35]  H. Vereecken,et al.  High-resolution imaging of a vineyard in south of France using ground penetrating radar, electromagnetic induction and electrical resistivity tomography , 2012 .

[36]  Evert C. Slob,et al.  Filtering Soil Surface and Antenna Effects From GPR Data to Enhance Landmine Detection , 2007, IEEE Transactions on Geoscience and Remote Sensing.

[37]  Sébastien Lambot,et al.  Coupling of dielectric mixing models with full-wave ground-penetrating radar signal inversion for sandy-soil-moisture estimation , 2012 .

[38]  Marnik Vanclooster,et al.  Modeling of ground-penetrating Radar for accurate characterization of subsurface electric properties , 2004, IEEE Transactions on Geoscience and Remote Sensing.

[39]  N. Spycher,et al.  Fluid flow and reactive transport around potential nuclear waste emplacement tunnels at Yucca Mountain, Nevada. , 2003, Journal of contaminant hydrology.

[40]  Norman Wagner,et al.  Experimental Investigations on the Frequency- and Temperature-Dependent Dielectric Material Properties of Soil , 2011, IEEE Transactions on Geoscience and Remote Sensing.

[41]  S. Moysey.  Hydrologic trajectories in transient ground-penetrating-radar reflection data , 2010 .

[42]  D. Or,et al.  Geometrical factors and interfacial processes affecting complex dielectric permittivity of partially saturated porous media , 2006 .

[43]  Dani Or,et al.  Ground-penetrating radar measurement of soil water content dynamics using a suspended horn antenna , 2004, IEEE Transactions on Geoscience and Remote Sensing.

[44]  A. Stogryn,et al.  Equations for Calculating the Dielectric Constant of Saline Water (Correspondence) , 1971 .

[45]  D. Hillel,et al.  A SIMULATION STUDY OF THE DRYING‐FRONT PHENOMENON , 1974 .