Geoelectrical constraints on radar probing of shallow water-saturated zones within karstified carbonates in semi-arid environments

Damayanti Mukherjee, Essam Heggy, Shuhab D. Khan

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Shallowcarbonates are of utmost importance as potential sources of groundwater in karstified semi-arid terrains. Ground-Penetrating Radar (GPR) is being increasingly used as a prominentmapping tool in such environments. However, its potential in exploring and identifying shallow water-saturated zones (WSZs) in carbonates is constrained by the geoelectrical properties of carbonate soils as a function of moisture content. We report results of a case study that includes laboratory geoelectrical characterization and their comparison to in situ GPR attenuationmeasurements performed on Cretaceous Edwards Formation rudist mounds in central Texas, which we hypothesize as analogs for water-bearing formations in semi-arid karstified carbonate terrains. Dielectric measurements on field-collected rock samples carried out in the laboratory under controlled conditions of moisture saturation suggest that real and imaginary parts of dielectric constants of rocks with higher porosity and/or permeability have steeper dependence on poremoisture content; they produce better dielectric contrasts but allow shallower penetration. Our analyses suggest that within carbonates, dielectric contrasts improve with decrease in sounding frequency and/or increase in moisture content; and the relationship between dielectric permittivity and moisture content may be represented by 3rd order polynomial equations. GPR surveys using a wide-band 400 MHz antenna reveal subsurface mound morphologies with heights of ~1-2m and basal diameters of ~8-10mresembling outcrop analogs. Eachmound appears to be composed of smaller amalgamated lithounits that seem geoelectrically similar. Amplitudes decays of the backscattered radar signal correlate to moisture distribution. Measuring the differences in signal attenuation allows differentiation between saturated and non-saturated zones. Velocity analyses of GPR profiles enable estimation of moisture distribution in the vicinity of themounds. Optimal delineation and production of high-resolution GPR data up to a depth of ~10m were observed for a sounding frequency of ~250 MHz with moisture content of ~5% by weight. Below this moisture level, the dielectric contrast is insufficient to uniquely identify water-saturated zones from the surrounding geoelectrical context, and above it, the radar signal is substantially attenuated leading to a total inefficiency of the method.

Original languageEnglish
Pages (from-to)181-191
Number of pages11
JournalJournal of Applied Geophysics
Volume70
Issue number3
DOIs
Publication statusPublished - 2010
Externally publishedYes

Fingerprint

ground penetrating radar
phreatic zone
arid environment
shallow water
radar
carbonates
moisture
moisture content
carbonate
sounding
rocks
permittivity
analogs
delineation
outcrops
radar data
ground water
rock
water
antenna

Keywords

  • Carbonate
  • Dielectric permittivity
  • GPR
  • Moisture
  • Porosity

ASJC Scopus subject areas

  • Geophysics

Cite this

Geoelectrical constraints on radar probing of shallow water-saturated zones within karstified carbonates in semi-arid environments. / Mukherjee, Damayanti; Heggy, Essam; Khan, Shuhab D.

In: Journal of Applied Geophysics, Vol. 70, No. 3, 2010, p. 181-191.

Research output: Contribution to journalArticle

@article{32fa3bc583f84d84b61246d357d4d2d7,
title = "Geoelectrical constraints on radar probing of shallow water-saturated zones within karstified carbonates in semi-arid environments",
abstract = "Shallowcarbonates are of utmost importance as potential sources of groundwater in karstified semi-arid terrains. Ground-Penetrating Radar (GPR) is being increasingly used as a prominentmapping tool in such environments. However, its potential in exploring and identifying shallow water-saturated zones (WSZs) in carbonates is constrained by the geoelectrical properties of carbonate soils as a function of moisture content. We report results of a case study that includes laboratory geoelectrical characterization and their comparison to in situ GPR attenuationmeasurements performed on Cretaceous Edwards Formation rudist mounds in central Texas, which we hypothesize as analogs for water-bearing formations in semi-arid karstified carbonate terrains. Dielectric measurements on field-collected rock samples carried out in the laboratory under controlled conditions of moisture saturation suggest that real and imaginary parts of dielectric constants of rocks with higher porosity and/or permeability have steeper dependence on poremoisture content; they produce better dielectric contrasts but allow shallower penetration. Our analyses suggest that within carbonates, dielectric contrasts improve with decrease in sounding frequency and/or increase in moisture content; and the relationship between dielectric permittivity and moisture content may be represented by 3rd order polynomial equations. GPR surveys using a wide-band 400 MHz antenna reveal subsurface mound morphologies with heights of ~1-2m and basal diameters of ~8-10mresembling outcrop analogs. Eachmound appears to be composed of smaller amalgamated lithounits that seem geoelectrically similar. Amplitudes decays of the backscattered radar signal correlate to moisture distribution. Measuring the differences in signal attenuation allows differentiation between saturated and non-saturated zones. Velocity analyses of GPR profiles enable estimation of moisture distribution in the vicinity of themounds. Optimal delineation and production of high-resolution GPR data up to a depth of ~10m were observed for a sounding frequency of ~250 MHz with moisture content of ~5{\%} by weight. Below this moisture level, the dielectric contrast is insufficient to uniquely identify water-saturated zones from the surrounding geoelectrical context, and above it, the radar signal is substantially attenuated leading to a total inefficiency of the method.",
keywords = "Carbonate, Dielectric permittivity, GPR, Moisture, Porosity",
author = "Damayanti Mukherjee and Essam Heggy and Khan, {Shuhab D.}",
year = "2010",
doi = "10.1016/j.jappgeo.2009.11.005",
language = "English",
volume = "70",
pages = "181--191",
journal = "Journal of Applied Geophysics",
issn = "0926-9851",
publisher = "Elsevier",
number = "3",

}

TY - JOUR

T1 - Geoelectrical constraints on radar probing of shallow water-saturated zones within karstified carbonates in semi-arid environments

AU - Mukherjee, Damayanti

AU - Heggy, Essam

AU - Khan, Shuhab D.

PY - 2010

Y1 - 2010

N2 - Shallowcarbonates are of utmost importance as potential sources of groundwater in karstified semi-arid terrains. Ground-Penetrating Radar (GPR) is being increasingly used as a prominentmapping tool in such environments. However, its potential in exploring and identifying shallow water-saturated zones (WSZs) in carbonates is constrained by the geoelectrical properties of carbonate soils as a function of moisture content. We report results of a case study that includes laboratory geoelectrical characterization and their comparison to in situ GPR attenuationmeasurements performed on Cretaceous Edwards Formation rudist mounds in central Texas, which we hypothesize as analogs for water-bearing formations in semi-arid karstified carbonate terrains. Dielectric measurements on field-collected rock samples carried out in the laboratory under controlled conditions of moisture saturation suggest that real and imaginary parts of dielectric constants of rocks with higher porosity and/or permeability have steeper dependence on poremoisture content; they produce better dielectric contrasts but allow shallower penetration. Our analyses suggest that within carbonates, dielectric contrasts improve with decrease in sounding frequency and/or increase in moisture content; and the relationship between dielectric permittivity and moisture content may be represented by 3rd order polynomial equations. GPR surveys using a wide-band 400 MHz antenna reveal subsurface mound morphologies with heights of ~1-2m and basal diameters of ~8-10mresembling outcrop analogs. Eachmound appears to be composed of smaller amalgamated lithounits that seem geoelectrically similar. Amplitudes decays of the backscattered radar signal correlate to moisture distribution. Measuring the differences in signal attenuation allows differentiation between saturated and non-saturated zones. Velocity analyses of GPR profiles enable estimation of moisture distribution in the vicinity of themounds. Optimal delineation and production of high-resolution GPR data up to a depth of ~10m were observed for a sounding frequency of ~250 MHz with moisture content of ~5% by weight. Below this moisture level, the dielectric contrast is insufficient to uniquely identify water-saturated zones from the surrounding geoelectrical context, and above it, the radar signal is substantially attenuated leading to a total inefficiency of the method.

AB - Shallowcarbonates are of utmost importance as potential sources of groundwater in karstified semi-arid terrains. Ground-Penetrating Radar (GPR) is being increasingly used as a prominentmapping tool in such environments. However, its potential in exploring and identifying shallow water-saturated zones (WSZs) in carbonates is constrained by the geoelectrical properties of carbonate soils as a function of moisture content. We report results of a case study that includes laboratory geoelectrical characterization and their comparison to in situ GPR attenuationmeasurements performed on Cretaceous Edwards Formation rudist mounds in central Texas, which we hypothesize as analogs for water-bearing formations in semi-arid karstified carbonate terrains. Dielectric measurements on field-collected rock samples carried out in the laboratory under controlled conditions of moisture saturation suggest that real and imaginary parts of dielectric constants of rocks with higher porosity and/or permeability have steeper dependence on poremoisture content; they produce better dielectric contrasts but allow shallower penetration. Our analyses suggest that within carbonates, dielectric contrasts improve with decrease in sounding frequency and/or increase in moisture content; and the relationship between dielectric permittivity and moisture content may be represented by 3rd order polynomial equations. GPR surveys using a wide-band 400 MHz antenna reveal subsurface mound morphologies with heights of ~1-2m and basal diameters of ~8-10mresembling outcrop analogs. Eachmound appears to be composed of smaller amalgamated lithounits that seem geoelectrically similar. Amplitudes decays of the backscattered radar signal correlate to moisture distribution. Measuring the differences in signal attenuation allows differentiation between saturated and non-saturated zones. Velocity analyses of GPR profiles enable estimation of moisture distribution in the vicinity of themounds. Optimal delineation and production of high-resolution GPR data up to a depth of ~10m were observed for a sounding frequency of ~250 MHz with moisture content of ~5% by weight. Below this moisture level, the dielectric contrast is insufficient to uniquely identify water-saturated zones from the surrounding geoelectrical context, and above it, the radar signal is substantially attenuated leading to a total inefficiency of the method.

KW - Carbonate

KW - Dielectric permittivity

KW - GPR

KW - Moisture

KW - Porosity

UR - http://www.scopus.com/inward/record.url?scp=77958184183&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=77958184183&partnerID=8YFLogxK

U2 - 10.1016/j.jappgeo.2009.11.005

DO - 10.1016/j.jappgeo.2009.11.005

M3 - Article

AN - SCOPUS:77958184183

VL - 70

SP - 181

EP - 191

JO - Journal of Applied Geophysics

JF - Journal of Applied Geophysics

SN - 0926-9851

IS - 3

ER -