Papers by Binayak Mohanty
Water Resources Research, 2008
A Markov chain Monte Carlo (MCMC) based algorithm was developed to derive upscaled land surface p... more A Markov chain Monte Carlo (MCMC) based algorithm was developed to derive upscaled land surface parameters for a soil‐vegetation‐atmosphere‐transfer (SVAT) model using time series data of satellite‐measured atmospheric forcings (e.g., precipitation), and land surface states (e.g., soil moisture and vegetation). This study focuses especially on the evaluation of soil moisture measurements of the Aqua satellite based Advanced Microwave Scanning Radiometer (AMSR‐E) instrument using the new MCMC‐based scaling algorithm. Soil moisture evolution was modeled at a spatial scale comparable to the AMSR‐E soil moisture product, with the hypothesis that the characterization of soil microwave emissions and their variations with space and time on soil surface within the AMSR‐E footprint can be represented by an ensemble of upscaled soil hydraulic parameters. We demonstrated the features of the MCMC‐based parameter upscaling algorithm (from field to satellite footprint scale) within a SVAT model f...
Water Resources Research, 2002
Estimation of effective/average soil hydraulic properties for large land areas is an outstanding ... more Estimation of effective/average soil hydraulic properties for large land areas is an outstanding issue in hydrologic modeling. The goal of this study is to provide flow‐specific rules and guidelines for upscaling soil hydraulic properties in an areally heterogeneous field. In this study, we examined the impact of areal heterogeneity of soil hydraulic parameters on soil ensemble behavior for steady state evaporation and infiltration. The specific objectives of this study are (1) to address the impact of averaging methods of shape parameters and parameter correlation on ensemble behavior of steady state flow in an areally heterogeneous field and (2) to investigate the effectiveness of the “average parameters” in terms of the degree of correlation between hydraulic property parameters for the steady state evaporation and infiltration in unsaturated soil. Using an analytical solution of Richards' equation, the ensemble characteristics and flow dynamics based on average hydraulic pro...
Water Resources Research, 2010
Process‐based soil hydrologic models require input of saturated hydraulic conductivity (Ksat). Ho... more Process‐based soil hydrologic models require input of saturated hydraulic conductivity (Ksat). However, model users often have limited access to measured data and thus use published or estimated values for many site‐specific hydrologic and environmental applications. We proposed an algorithm that uses the Karhunen‐Loève expansion (KLE) in conjunction with the Markov chain Monte Carlo (MCMC) technique, which employs measured soil moisture values to characterize the saturated hydraulic conductivity of an agricultural field at a 30 m resolution. The study domain is situated in the Walnut Creek watershed, Iowa, with soybean crop (in 2005) and well‐defined top (atmospheric) and bottom (groundwater) boundary conditions. The KLE algorithm parameterizes and generates Ksat fields with random correlation lengths that are used in the SWMS_3D model for predicting the soil moisture dynamics for two different scenarios: (1) the van Genuchten soil hydraulic parameters (except Ksat) are constant an...
Water Resources Research, 2003
In hydroclimate and land-atmospheric interaction models, effective hydraulic properties are neede... more In hydroclimate and land-atmospheric interaction models, effective hydraulic properties are needed at large grid scales. In this study, the effective soil hydraulic parameters of the areally heterogeneous soil formation are derived by conceptualizing the heterogeneous soil formation as an equivalent homogeneous medium and assuming that the equivalent homogeneous soil will approximately discharge the same total amount of flux and produce same average pressure head profile in the formation. As compared to previous effective hydraulic property studies, a specific feature of this study is that the derived effective hydraulic parameters are mean-gradient-dependent (i.e., vary across depth). Although areal soil heterogeneity was formulated as parallel homogeneous stream tubes in this study, our results appear to be consistent with the previous findings of meangradient unsaturated hydraulic conductivity [Yeh et al., 1985a, 1985b]. Three widely used hydraulic conductivity models were employed in this study, i.e., the Gardner model, the Brooks and Corey model, and the van Genuchten model. We examined the impact of parameter correlation, boundary condition (surface pressure head), and elevation above the water table on the effective saturated hydraulic conductivity and shape parameter. The correlation between the saturated hydraulic conductivity K s and the shape parameter a increases the effective saturated hydraulic conductivity, while it does not affect the effective a. The effective a is usually smaller than the mean value of a, while the effective K s can be smaller or larger than the mean value depending on no correlation or full correlation between K s and a fields, respectively. An important observation of this study is that Gardner and van Genuchten functions resulted in effective parameters, whereas it is difficult to define effective parameters for the Brooks Corey model since this model uses a piecewise-continuous profile for hydraulic conductivity.
Vadose Zone Journal, 2006
Soil moisture is an important hydrologic state variable critical to successful hydroclimatic and ... more Soil moisture is an important hydrologic state variable critical to successful hydroclimatic and environmental predictions. Soil moisture varies both in space and time because of spatio‐temporal variations in precipitation, soil properties, topographic features, and vegetation characteristics. In recent years, air‐ and space‐borne remote sensing campaigns have successfully demonstrated the use of passive microwave remote sensing to map soil moisture status near the soil surface (≈0–0.05 m below the ground) at various spatial scales. In this study root zone (e.g., ≈0–0.6 m below the ground) soil moisture distributions were estimated across the Little Washita watershed (Oklahoma) by assimilating near‐surface soil moisture data from remote sensing measurements using the Electronically Scanned Thinned Array Radiometer (ESTAR) with an ensemble Kalman filter (EnKF) technique coupled with a numerical one‐dimensional vadose zone flow model (HYDRUS‐ET). The resulting distributed root zone so...
Vadose Zone Journal, 2006
Hydraulic parameters of the vadose zone at a spatial resolution typically larger than 1 km 2 are ... more Hydraulic parameters of the vadose zone at a spatial resolution typically larger than 1 km 2 are a key input for land-atmosphere feedback schemes in soil-vegetation-atmosphere transfer (SVAT) models. Previous studies investigated the significance of first-and secondorder moments of soil hydraulic parameters on ''effective'' parameter estimation in heterogeneous soils at the landscape or remote-sensing footprint/pixel scale. In this study, we examined the impact of the skewness (third-order moment) of hydraulic parameter distributions on ''effective'' soil hydraulic parameter averaging schemes for steadystate vertical flow in heterogeneous soils in a flat landscape. The effective soil hydraulic parameter of the heterogeneous soil formation is obtained by conceptualizing the soil as an equivalent homogeneous medium. The averaging scheme requires that the effective homogeneous soil will discharge the same ensemble moisture flux across the soil surface. Using three widely used unsaturated hydraulic conductivity functions and various types of probability distribution functions to represent spatial variability for the nonlinear shape factor in the hydraulic conductivity function, we derive the effective parameter values. Numerical and field experimental results show that distribution skewness is also important in determining the upscaled effective parameters in addition to the mean and variance. Negative skewness enhances heterogeneity effects, which make the ''effective'' a parameter deviate more significantly from the arithmetic mean. In the case of negative skewness, a few small a values make the heterogeneous soil more permeable (with larger flux), which hence causes the ''effective'' heterogeneous system to deviate more from the homogeneous formation with arithmetic mean parameters.
Vadose Zone Journal, 2004
Dagan and Bresler (1983) and Bresler and Dagan (1983) developed models for water flow in the uppe... more Dagan and Bresler (1983) and Bresler and Dagan (1983) developed models for water flow in the upper In this study we investigate effective soil hydraulic parameter aversoil layer of spatially variable fields where spatial variaging schemes for steady-state flow with plant root water uptake in heterogeneous soils. "Effective" soil hydraulic parameters of a hetero-ability of the saturated hydraulic conductivity is asgeneous soil formation are obtained by conceptualizing the soil as sumed to take place in the horizontal plane. They found an equivalent homogeneous medium. The "effective" homogeneous that effective properties may be meaningful only under medium is only required to discharge the same ensemble-mean flux very restricted and special conditions, such as steady across the soil surface. One-dimensional flow at the local scale has gravitational flow where the effective saturated hydraubeen used as an approximation for various simplified problems under lic conductivity varies between the geometric mean and investigation (e.g., a shallow subsurface dominated by vertical flows). the arithmetic mean. Kim and Stricker (1996) employed The domain is assumed to be composed of homogeneous one-dimen-Monte Carlo simulation to investigate the independent sional soil columns without mutual interactions. Using Gardner's unand simultaneous effects of horizontal heterogeneity in saturated hydraulic conductivity model, we derive the effective value soil hydraulic properties and rainfall intensity on various for the parameter ␣. While root water uptake influences the overall water budget, its impact on the effective hydraulic parameter averag-statistical properties of the components of the one-dimening scheme was found to be secondary. Results show that the arithme-sional water budget for a large area up to 10 4 km 2. The tic mean of Gardner's ␣ is usually too large to serve as an effective effective hydraulic parameters were calculated by minparameter. Deviations of the effective parameter from the arithmetic imizing the squared differences of the capillary pressure mean become larger as the surface suction increases; that is, the profiles in the formation. Zhang et al. (1998) developed flow scenario switches from infiltration to evaporation. The results first-order stochastic models for stationary media using consistently show a smaller effective parameter for evaporation sceboth the Brooks-Corey and the Gardner-Russo hydraunarios than for infiltration scenarios. The effective parameter ␣ eff lic property models. Kim et al. (1997) investigated the decreases with an increase in the mean value of ␣. Spatial variability J. Zhu and B.P. Mohanty, Dep. of Biological and Agricultural Engi-formations for steady-state infiltration and evaporation. neering,
Vadose Zone Journal, 2002
factors. Kim and Stricker (1996) employed Monte Carlo simulation to investigate the independent a... more factors. Kim and Stricker (1996) employed Monte Carlo simulation to investigate the independent and simulta-For meso-or regional-scale Soil-Vegetation-Atmosphere Transfer neous effects of horizontal heterogeneity in soil hydrau-(SVAT) schemes in hydroclimatic models, pixel dimensions may range from several hundred square meters to several hundred square kilome-lic properties and rainfall intensity on various statistical ters. Pixel-scale soil hydraulic parameters and their accuracy are criti-properties of the components of the one-dimensional cal for the success of hydroclimatic and soil hydrologic models. This water budget for a large area up to 10 4 km 2. The effective study tries to answer a major question: What will be the effective and parameters in the hydraulic property functions can be average hydraulic properties for the entire pixel (or footprint of a redetermined by inversion (e.g., Yeh, 1989) or perturbamote sensor) consisting of several textures if the soil hydraulic propertion (Milly and Eagleson, 1987; Kim et al., 1997) methties can be estimated for each individual texture? In this study, we ods. Yeh (1989) studied the effect of soil heterogeneity examined the impact of areal heterogeneity in soil hydraulic parameon one-dimensional steady infiltration using the Gardters on soil ensemble behavior for steady-state evaporation and infilner exponential model (Gardner, 1958) for the unsatutration. Using the widely used van Genuchten model and hydraulic parated hydraulic conductivity. The effective hydraulic rameter statistics obtained from neural network-based pedotransfer functions (PTFs) for various soil textural classes, we address the im-parameters were calculated by minimizing the squared pact of areal hydraulic property heterogeneity on ensemble behavior differences of the capillary pressure profiles in the forand uncertainty in steady-state vertical flow in large-scale heterogemation. While the obtained parameters provided the neous fields. The various averaging schemes of van Genuchten parambest fit, they may not necessarily perform well in repreeters are compared with "effective parameters" calculated by concepsenting heterogeneous behavior of the soil because of tualizing the areally heterogeneous soil formation as an equivalent the highly nonlinear nature of the process. Kim et al. homogeneous medium that will discharge approximately the same (1997) investigated the impact of heterogeneity of the amount of ensemble flux of the heterogeneous soil. The impact of soil hydraulic properties on the spatially averaged water boundary conditions and parameter correlation on the effective pabudget of the unsaturated zone using a framework of rameters, as well as the accuracy and uncertainty of the averaging analytical solutions (Kim et al., 1996). Their results indischemes for the hydraulic parameters, are investigated and discussed. In light of our results, we suggest the following guidelines for van Ge-cated that the "effective" set of hydraulic parameters nuchten hydraulic parameter averaging: arithmetic means for K s and depends on the specific climate and the spatially uniform n, a value between arithmetic and geometric means for ␣ when K s and parameters, in addition to the obvious dependence on ␣ are highly correlated, and a value between geometric and harmonic the mean, variance, and covariances of the spatially means for ␣ when K s and ␣ are poorly correlated.
Journal of Hydrometeorology, 2007
In this study, the authors investigate effective soil hydraulic parameter averaging schemes for s... more In this study, the authors investigate effective soil hydraulic parameter averaging schemes for steady-state flow in heterogeneous shallow subsurfaces useful to land–atmosphere interaction modeling. “Effective” soil hydraulic parameters of the heterogeneous shallow subsurface are obtained by conceptualizing the soil as an equivalent homogeneous medium. It requires that the effective homogeneous soil discharges the same mean surface moisture flux (evaporation or infiltration) as the heterogeneous media. Using the simple Gardner unsaturated hydraulic conductivity function, the authors derive the effective value for the saturated hydraulic conductivity Ks or the shape factor α under various hydrologic scenarios and input hydraulic parameter statistics. Assuming one-dimensional vertical moisture movement in the shallow unsaturated soils, both scenarios of horizontal (across the surface landscape) and vertical (across the soil profile) heterogeneities are investigated. The effects of hyd...
Sinkholes and the Engineering and Environmental Impacts of Karst, Sep 22, 2005
An experimental rainfall simulation plot (7 x 14 m) in the Edwards Aquifer region of Texas was es... more An experimental rainfall simulation plot (7 x 14 m) in the Edwards Aquifer region of Texas was established in dense juniper land cover to measure the effects of brush clearing on runoff. This project includes the monitoring of lateral subsurface flow using a trench (2.5 m deep x 8 m ...
Journal of Environmental Quality, Nov 1, 2011
Biogeochemical dynamics in the vadose zone are poorly understood due to the transient nature of c... more Biogeochemical dynamics in the vadose zone are poorly understood due to the transient nature of chemical and hydrologic conditions, but are nonetheless critical to understanding chemical fate and transport. This study explored the effects of a soil layer on linked geochemical, hydrological, and microbiological processes. Three laboratory soil columns were constructed: a homogenized medium-grained sand, a homogenized organic-rich loam, and a sand-over-loam layered column. Upward and downward infiltration of water was evaluated during experiments to simulate rising water table and rainfall events respectively. In-situ collocated probes measured soil water content, matric potential, and Eh while water samples collected from the same locations were analyzed for Br − , Cl − , NO 3 − , SO 4 2− , NH 4 + , Fe 2+ , and total sulfide. Compared to homogenous columns, the presence of a soil layer altered the biogeochemistry and water flow of the system considerably. Enhanced biogeochemical cycling was observed in the layered column over the texturally homogeneous soil columns. Enumerations of iron and sulfate reducing bacteria showed 1-2 orders of magnitude greater community numbers in the layered column. Mineral and soil aggregate composites were most abundant near the soil-layer interface; the presence of which, likely contributed to an observed order-of-magnitude decrease in hydraulic conductivity. These findings show that quantifying coupled hydrologic-biogeochemical processes occurring at small-scale soil interfaces is critical to accurately describing and predicting chemical changes at the larger system scale. Findings also provide justification for considering soil layering in contaminant fate and transport models because of its potential to increase biodegradation and/or slow the rate of transport of contaminants.
AGU Fall Meeting Abstracts, Dec 1, 2003
Over the last hundred years, the semi-arid region of Southwestern United States has undergone a c... more Over the last hundred years, the semi-arid region of Southwestern United States has undergone a considerable change in landscape. The region that was once primarily covered by native grass has been invaded with brushy species, such as ash juniper (cedar) and mesquite. This brush encroachment has resulted in a major effect on the hydrologic cycle. With new brush species dominating
Physics and chemistry of the earth, 2001
ABSTRACT Temporal and spatial variability of water content in soil results from a complex interac... more ABSTRACT Temporal and spatial variability of water content in soil results from a complex interaction of different factors such as duration and frequency of rainfall, soil layering, vegetation, and topography. The objectives of this study were (i) to use a resistant median-polishing scheme to quantify the temporal variability of a depth and a horizontal location factor in an additive model, and (ii) to investigate the time stability of those two factors at a detailed temporal scale during different infiltration and redistributions cycles. Time series of water content were measured at 5 depths and 12 locations along a transect of 6 m using Time Domain Reflectometry (TDR). Measurements were repeated every 2-hours for 168 days under natural boundary conditions. At each time step, the mean water content of the soil profile, 5 depth factors and 12 location factors were estimated. The time series of these factors were qualitatively interpreted and related to the atmospheric and prevailing soil conditions. It was found that micro-heterogeneity plays an important role, even at this small plot-scale. The relative contributions of the factors were dependent on the antecedent soil moisture conditions. Also, the ratio of the deterministic variance, i.e., variance explained by the deterministic factors, of water content to the observed variance is variable in time.
Soil Science, Mar 1, 1996
Unsaturated hydraulic properties of field soils are needed for water flow and solute transport ca... more Unsaturated hydraulic properties of field soils are needed for water flow and solute transport calculations in variably saturated soils. The purpose of this study was to quantify the spatial variability and spatial crosscorrelation of estimated parameter values of a flexible retention model that was fitted to measured retention data. Moisture retention characteristic (MRC) curves were measured on 100&m' undisturbed soil cores collected at 180 locations along a 31-m-long transect in a three-layered soil profile at depths of 0.1, 0.5, and 0.9 m. Sampling intervals in the horizontal direction were, alternately, 0.1 and 0.9 m. Saturated hydraulic conductivity (K,) was determined on the same soil cores using a constant head permeameter.The drying part of the MRC curves was described by the four-parameter retention model of van Genuchten with fitting parameters,. namely 0, O,, a, and n. Spatial variability of the five parameters, 0, B,, a, n, and K,, was investigated for tbe three horizons using conventional statistics and geostatistical techniques. Maximum coefficient of variation (CV) was found for K, i.e., 599%, 322%, and 897% for the O.l-, 0.5-, and 0.9-m soil depths, respectively. Macropores and small sampling volume contributed to this large variability of K,. When all three soil depths are considered, residual water content (0,) and shape factor a showed moderate heterogeneity with a maximum CV of 156 and 53%, respectively. Small spatial heterogeneity was observed for shape factor n and saturated water content B,, with a maximum CV of 22 (for 0.1-m depth) and 8% (for 0.9-m depth), respectively. Most hydraulic parameters at different layers exhibited convex experimental semivariograms that could be described by means of spherical models, with a spatial range between 4 and 7 m.The correlation scales for cross-semivariograms for pairs of cross-correlated parameters were found to be of similar magnitude to those pertaining to the direct semivariograms of correlated variables.
Transactions of the ASABE, 2012
A multiscale Bayesian neural network (BNN) based algorithm was applied to obtain soil hydraulic p... more A multiscale Bayesian neural network (BNN) based algorithm was applied to obtain soil hydraulic parameters at multiple scales in the Rio Grande basin (near Picacho Mountain, approximately 11 km northwest of Las Cruces, New Mexico). Point-scale measurements were upscaled to 30 m and 1 km resolutions. These scaled parameters were used in a physically based hydrologic model as inputs to obtain soil moisture states across the study area. The test sites were chosen to provide variety in terrain, land use characteristics, vegetation, soil types, and soil distribution patterns. In order to validate the effectiveness of the upscaled soil water retention parameters, and thus the soil hydraulic parameters, hydrologic simulations were conducted using the HYDRUS-3D hydrologic simulation software. Outputs from the hydrologic simulations using the scaled parameters were compared with those using data from SSURGO and STATSGO soil maps. The BNN-based upscaling algorithm for soil retention parameters from point-scale measurements to 30 m and 1 km, resolutions performed reasonably well (Pearson's R > 0.6) at both scales. High correlations (>0.6) between the simulated soil moisture values based on the upscaled and the soil map-derived soil hydraulic parameters show that the methodology is applicable to semi-arid regions to obtain effective soil hydraulic parameter values at coarse scales from fine-scale measurements of soil texture, structure, and retention data.
The goal of this project is to gain further understanding of soil moisture/temperature dynamics a... more The goal of this project is to gain further understanding of soil moisture/temperature dynamics at different spatio-temporal scales and physical controls/parameters.We created a comprehensive GIS database, which has been accessed extensively by NASA Land Surface Hydrology investigators (and others), is located at the following URL: http://www.essc.psu.edu/nasalsh. For soil moisture field experiments such as SGP97, SGP99, SMEX02, and SMEX03, cartographic products were designed for multiple applications, both pre- and post-mission. Premission applications included flight line planning and field operations logistics, as well as general insight into the extent and distribution of soil, vegetation, and topographic properties for the study areas. The cartographic products were created from original spatial information resources that were imported into Adobe Illustrator, where the maps were created and PDF versions were made for distribution and download.
AGU Fall Meeting Abstracts, Dec 1, 2006
ABSTRACT Pedo Transfer Functions (PTFs) based on Artificial Neural Networks (ANNs) have been used... more ABSTRACT Pedo Transfer Functions (PTFs) based on Artificial Neural Networks (ANNs) have been used in the field of hydrology for some time. However, while most previous studies derive and adopt these parameters at matching spatial scales (1:1) of input and output data, here we present two methodologies to derive the soil water retention function at the point or local scale using PTFs trained with coarser scale input data. In the first study, a conventional ANN was trained using soil texture and bulk density data from the SSURGO database (scale 1:24,000) and then used for predicting the soil water contents at different pressure heads with point scale data (1:1) inputs. Suitable bias correction was applied to the resulting output and used to construct the van Genuchten soil water characteristic curve. The results show good agreement between the soil water retention curves constructed from the ANN-based PTFs and the field observations at the local scale. In the second study we employed a Markov Chain Monte Carlo (MCMC) based Bayesian Neural Network to derive the soil water content values. While conventional ANN training attempts to describe the target variable as a function of the input vector and the training weights, Bayesian training attempts to update the weight vector with information available in the data. Comparisons of the outputs from the two methodologies are presented and their respective advantages and disadvantages are highlighted. These methods have potential as suitable tools to tackle the dual problems of parameter estimation and their scaling in one simple package.
AGUFM, Dec 1, 2009
... Authors: Jana, RB; Mohanty, BP. ... Further, the theoretical basis is validated with data fro... more ... Authors: Jana, RB; Mohanty, BP. ... Further, the theoretical basis is validated with data from two different sites - one at the Panola Mountain Research Watershed in Georgia, and the other in the Little Washita watershed in Oklahoma. ...
AGUFM, Dec 1, 2011
ABSTRACT Soil moisture and soil hydrologic fluxes (infiltration, ET, runoff) are affected at diff... more ABSTRACT Soil moisture and soil hydrologic fluxes (infiltration, ET, runoff) are affected at different scales by the spatial variability of influencing factors such as soil, topography, vegetation, and climatic forcings such as precipitation and temperature patterns. Understanding the nature of the linkage between these physical controls and the soil hydraulic parameters is critical in developing efficient scaling schemes for effective hydrologic modeling at large domains. We present results from a multi-location, multi-scale study designed to tease out the dominant physical control of soil hydraulic parameter variability at each scale of interest, and the evolution of the dominance with scale. Mathematical techniques such as Wavelet analysis and Karhunen-Loeve expansion are applied to bring out the extent of influence of the physical controls on the distribution signatures of the hydraulic parameters at the various scales. Data from diverse hydro-climatic locations across the globe, at various scales, derived from multiple platforms/sensors such as in-situ sensors, airborne remote sensors, and various satellite-borne remote sensors are used in this study to improve our understanding of the processes governing the hydraulic variability of soils. The study also considers the correlations among the soil hydraulic parameters, and their progression with change in scale. Further, we test the efficacy of certain existing soil hydraulic parameter scaling algorithms with regard to preserving these relationships (both among the hydraulic parameters, and with the physical controls) and provide guidelines for their usage at specific scales.
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Papers by Binayak Mohanty