The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Frederick D Daylewis - One of the best experts on this subject based on the ideXlab platform.
-
time lapse imaging of saline tracer transport in fractured rock using difference attenuation radar tomography
Water Resources Research, 2003Co-Authors: Frederick D Daylewis, John W Lane, Jerry M Harris, Steven M GorelickAbstract:[1] Accurate characterization of fractured-rock aquifer heterogeneity remains one of the most challenging and important problems in groundwater Hydrology. We demonstrate a promising strategy to identify preferential flow paths in fractured rock using a combination of geophysical monitoring and conventional hydrogeologic tests. Cross-well differenceattenuation ground-penetrating radar was used to monitor saline-tracer migration in an experiment at the U.S. Geological Survey Fractured Rock Hydrology Research Site in Grafton County, New Hampshire. Radar data sets were collected every 10 min in three adjoining planes for 5 hours during each of 12 tracer tests. An innovative inversion method accounts for data acquisition times and temporal changes in attenuation during data collection. The inverse algorithm minimizes a combination of two functions. The first is the sum of weighted squared data residuals. Second is a measure of solution complexity based on an a priori space-time covariance function, subject to constraints that limit radarattenuation changes to regions of the tomograms traversed by high difference-attenuation ray paths. The time series of tomograms indicate relative tracer concentrations and tracer arrival times in the image planes; from these we infer the presence and location of a preferential flow path within a previously identified zone of transmissive fractures. These results provide new insights into solute channeling and the nature of aquifer heterogeneity at the site. INDEX TERMS: 0910 Exploration Geophysics: Data processing; 0915 Exploration Geophysics: Downhole methods; 1829 Hydrology: Groundwater Hydrology; 1832 Hydrology: Groundwater transport; 1894 Hydrology: Instruments and techniques; KEYWORDS: radar tomography, fractured rock, ground-penetrating radar, geophysics, hydrogeophysics
Chi-te Chen - One of the best experts on this subject based on the ideXlab platform.
-
Mapping snow water equivalent by combining a spatially distributed snow Hydrology model with passive microwave remote-sensing data
IEEE Transactions on Geoscience and Remote Sensing, 1999Co-Authors: L.l. Wilson, Leung Tsang, Jenq-neng Hwang, Chi-te ChenAbstract:An algorithm to incorporate passive microwave remote-sensing measurements within a spatially distributed snow Hydrology model to provide estimates of the spatial distribution of snow water equivalent (SWE) as a function of time is implemented. A priori information provided by the snow Hydrology model is used to provide initial estimates of snow parameters from brightness temperature measurements. The algorithm is illustrated by applying it to a mountainous region. The passive microwave remote-sensing measurements are 25-km resolution (grid). However, in mountain regions, the spatial variability of SWE over a 25-km grid is large due to topographic influences. On the other hand, the snow Hydrology model has built-in topographic information and the capability to estimate SWE at a 1-km resolution. In their work, the snow Hydrology SWE estimates are updated and corrected using Special Sensor Microwave/Imager (SSM/I) passive microwave remote-sensing measurements. The method is applied to the Upper Rio Grande River Basin in the mountains of Colorado. The change in prediction of SWE from Hydrology modeling with and without updating is compared with measurements from two SNOwpack TELemetry (SNOTEL) sites in and near the basin. The results indicate that the method incorporating the remote-sensing measurements into the Hydrology model is able to more closely estimate the temporal evolution of the measured values of SWE as a function of time.
Steven M Gorelick - One of the best experts on this subject based on the ideXlab platform.
-
time lapse imaging of saline tracer transport in fractured rock using difference attenuation radar tomography
Water Resources Research, 2003Co-Authors: Frederick D Daylewis, John W Lane, Jerry M Harris, Steven M GorelickAbstract:[1] Accurate characterization of fractured-rock aquifer heterogeneity remains one of the most challenging and important problems in groundwater Hydrology. We demonstrate a promising strategy to identify preferential flow paths in fractured rock using a combination of geophysical monitoring and conventional hydrogeologic tests. Cross-well differenceattenuation ground-penetrating radar was used to monitor saline-tracer migration in an experiment at the U.S. Geological Survey Fractured Rock Hydrology Research Site in Grafton County, New Hampshire. Radar data sets were collected every 10 min in three adjoining planes for 5 hours during each of 12 tracer tests. An innovative inversion method accounts for data acquisition times and temporal changes in attenuation during data collection. The inverse algorithm minimizes a combination of two functions. The first is the sum of weighted squared data residuals. Second is a measure of solution complexity based on an a priori space-time covariance function, subject to constraints that limit radarattenuation changes to regions of the tomograms traversed by high difference-attenuation ray paths. The time series of tomograms indicate relative tracer concentrations and tracer arrival times in the image planes; from these we infer the presence and location of a preferential flow path within a previously identified zone of transmissive fractures. These results provide new insights into solute channeling and the nature of aquifer heterogeneity at the site. INDEX TERMS: 0910 Exploration Geophysics: Data processing; 0915 Exploration Geophysics: Downhole methods; 1829 Hydrology: Groundwater Hydrology; 1832 Hydrology: Groundwater transport; 1894 Hydrology: Instruments and techniques; KEYWORDS: radar tomography, fractured rock, ground-penetrating radar, geophysics, hydrogeophysics
L.l. Wilson - One of the best experts on this subject based on the ideXlab platform.
-
Mapping snow water equivalent by combining a spatially distributed snow Hydrology model with passive microwave remote-sensing data
IEEE Transactions on Geoscience and Remote Sensing, 1999Co-Authors: L.l. Wilson, Leung Tsang, Jenq-neng Hwang, Chi-te ChenAbstract:An algorithm to incorporate passive microwave remote-sensing measurements within a spatially distributed snow Hydrology model to provide estimates of the spatial distribution of snow water equivalent (SWE) as a function of time is implemented. A priori information provided by the snow Hydrology model is used to provide initial estimates of snow parameters from brightness temperature measurements. The algorithm is illustrated by applying it to a mountainous region. The passive microwave remote-sensing measurements are 25-km resolution (grid). However, in mountain regions, the spatial variability of SWE over a 25-km grid is large due to topographic influences. On the other hand, the snow Hydrology model has built-in topographic information and the capability to estimate SWE at a 1-km resolution. In their work, the snow Hydrology SWE estimates are updated and corrected using Special Sensor Microwave/Imager (SSM/I) passive microwave remote-sensing measurements. The method is applied to the Upper Rio Grande River Basin in the mountains of Colorado. The change in prediction of SWE from Hydrology modeling with and without updating is compared with measurements from two SNOwpack TELemetry (SNOTEL) sites in and near the basin. The results indicate that the method incorporating the remote-sensing measurements into the Hydrology model is able to more closely estimate the temporal evolution of the measured values of SWE as a function of time.
John S. Selker - One of the best experts on this subject based on the ideXlab platform.
-
relationships between gas liquid interfacial surface area liquid saturation and light transmission in variably saturated porous media
Water Resources Research, 2002Co-Authors: Michael R Niemet, Mark L Rockhold, Noam Weisbrod, John S. SelkerAbstract:[1] Liquid saturation and gas-liquid interfacial area are important parameters for evaluating the transport and fate of contaminants in unsaturated subsurface environments. Recent findings indicate that interfacial surface area controls the relative degree of transmitted light in laboratory systems containing translucent porous media. Equations are derived to estimate the specific gas-liquid interfacial area from the area under the primarydrainage branch of the Seff-h characteristic curve as parameterized using common water retention functions. The total area under the curve provides the maximum available specific gas-liquid interfacial area available at residual saturation, which can be incorporated into the relationship to determine the gas-liquid interfacial area at intermediate degrees of saturation via light transmission. Experimental results, and analysis of external data sets, support these findings. Closed-form relationships are presented as enhancements to a recent method for determination of liquid saturations above residual using light transmission. A physically based model is developed and tested for the quantification of liquid contents below residual saturation. INDEX TERMS: 1829 Hydrology: Groundwater Hydrology; 1866 Hydrology: Soil moisture; 1875 Hydrology: Unsaturated zone; 1894 Hydrology: Instruments and techniques; KEYWORDS: light transmission, gas-liquid interfacial surface area, liquid saturation, residual saturation, unsaturated porous media, characteristic curve
