-
NRCS, National Soil Survey Center 100 Centennial Mall North;
Federal Building, Room 152
Lincoln, NE 68508-3866 Phone: 402-437-5499; Fax:
402-437-5336
An Equal Opportunity Provider and Employer
Subject: MGT -- Geophysical Field Assistance Date: August 29,
2016
To: Ann English File Code: 330-20-7 State Conservationist
Natural Resources Conservation Service Columbia, South Carolina
Purpose: To provide technical assistance and training in the use
of ground-penetrating radar (GPR) and electromagnetic induction
(EMI) techniques with the soils staff located in Laurens County,
South Carolina while assessing soil properties. Participants:
Debbie Anderson, Soil Survey Regional Director (SSR-3), NRCS,
Raleigh, NC Lance Brewington, MLRA Soil Survey Leader, NRCS,
Laurens, SC Dennis DeFrancesco, Retired Soil Scientist, NRCS, SC
Gary Hankins, Soil Scientist, NRCS, Laurens, SC Kamara Holmes,
State Soil Scientist, NRCS, Columbia, SC Emory Holsonback, Area
Resource Soil Scientist, NRCS, Laurens, SC Greg Taylor, Senior
Regional Soil Scientist (SSR-3), NRCS, Raleigh, NC Wes Tuttle, Soil
Scientist (Geophysical), NSSC, NRCS, Wilkesboro, NC Activities: All
field activities were completed on March 8-11, 2016. Summary: 1.
The MLRA soils office located in Laurens, SC has a newly acquired
conductivity meter
(Profiler EMP-400 manufactured by Geophysical Survey Systems,
Inc., Nashua, NH). Apparent conductivity surveys were completed at
multiple sites as associations were made between changes in
apparent conductivity (ECa) and changes in soil properties
including depth to bedrock and changes in clay and moisture. Deeper
soils and soils with more clay and moisture resulted in higher ECa
measurements. Ground-penetrating radar surveys were also completed
to assess changes in depth to bedrock and associated changes in
apparent conductivity. The NRCS staff were very receptive to new
methods of soils investigations and minimally invasive procedures
resulting from the use of ground-penetrating radar (GPR) and
electromagnetic induction (EMI). The NRCS staff demonstrated the
ability and an eagerness to conduct EMI investigations
independently while yielding meaningful interpretations. Follow-up
training is recommended in the use of EMI techniques to help
reinforce operational techniques and data processing.
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Ann English Page 2 2. Geophysical interpretations are considered
preliminary estimates of site conditions. The
results of all geophysical investigations are interpretive and
do not substitute for direct soil borings. The use of geophysical
methods can reduce the number of soil observations, direct their
placement, and supplement their interpretations. Interpretations
should be verified by ground-truth observations.
It was a pleasure for Wes Tuttle to work in South Carolina with
members of your fine staff. DAVID HOOVER Acting Director National
Soil Survey Center Attachment: Technical Report cc: Debbie
Anderson, Soil Survey Regional Director (SSR-3), NRCS, Raleigh, NC
Lance Brewington, MLRA Soil Survey Leader, NRCS, Laurens, SC Kamara
Holmes, State Soil Scientist, NRCS, Columbia, SC Zamir Libohova,
Research Soil Scientist (NSSC Liaison), NSSC, MS 41, NRCS, Lincoln,
NE Michael Robotham, National Leader, Technical Soil Services, SSD,
NRCS, Lincoln, NE John “Wes” Tuttle, Soil Scientist (Geophysical),
NSSC, NRCS, Wilkesboro, NC Doug Wysocki, National Leader, Soil
Survey Research and Laboratory, NSSC, MS 41, NRCS,
Lincoln, NE
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1
This technical report was prepared by Wes Tuttle Geophysical
Soil Scientist, USDA-NRCS-NSSC, Wilkesboro, North Carolina
Equipment The radar unit is the TerraSIRch SIR (Subsurface
Interface Radar) System-3000, manufactured by Geophysical Survey
Systems, Inc.1 Morey (1974), Doolittle (1987), and Daniels (1996)
have discussed the use and operation of GPR. The SIR System-3000
consists of a digital control unit (DC-3000) with keypad, color
SVGA video screen, and connector panel. A 10.8-volt Lithium-Ion
rechargeable battery powers the system. This unit is backpack
portable and, with an antenna, requires two people to operate. The
antenna used in this study has a center frequency of 200 MHz. The
RADAN for Windows (version 7.0) software program was used to
process the radar records (Geophysical Survey Systems, Inc, 2008).1
Processing included color transformation, surface normalization,
time-zero adjustment and range gain adjustments. The Profiler
EMP-400 sensor (hereafter referred to as the Profiler) is
manufactured by Geophysical Survey Systems, Inc. (Nashua, NH) (see
Photo 1). 1 Operating procedures for the Profiler are described by
Geophysical Survey Systems, Inc. (2008). The Profiler has a 1.22 m
(4.0 ft) intercoil spacing and operates at frequencies ranging from
1 to 16 kHz. It weighs about 4.5 kg (9.9lbs). The Profiler is a
multifrequency EMI meter that can simultaneously record data in as
many as three discrete frequencies. For each frequency, both
in-phase (susceptibility) and quadrature phase (apparent
conductivity, EC3) data are recorded. The calibration of the
Profiler is optimized for 15 kHz and, as a consequence, ECa is most
accurately measured at this frequency (Dan Delea, GSSI, personal
communication). Surveys can be conducted with the sensor held in
the shallower-sensing HDO or the deeper-sensing VDO orientations.
The sensor's electronics are controlled via Bluetooth
communications with a Trimble TDS RECON-400 or a Trimble Nomad
Personal Data Assistant (PDA). 1 To collect geo-referenced data,
the PDA is configured with an integral l2-channel WAAS (Wide Area
Augmentation System) GPS. Geonics Limited manufactures the EM38
meter. This meter is portable and requires only one person to
operate. No ground contact is required with this meter. McNeill
(1980) and Geonics Limited (1998) have described principles of
operation for the EM38 meter. Lateral resolution is approximately
equal to its intercoil spacing. The EM38 meter has a 1 m intercoil
spacing and operates at a frequency of 14,600 Hz. When placed on
the soil surface, this instrument has a theoretical penetration
depth of about 0.75 and 1.5 m in the horizontal and vertical dipole
orientations, respectively (Geonics Limited, 1998). Values of
apparent conductivity are expressed in millisiemens per meter
(mS/m). To help summarize the results of this study, the SURFER for
Windows (version 8.0 and version 11.0) developed by Golden
Software, Inc. was used to construct two-dimensional simulations.
Grids were created using kriging methods with an octant search.
Ground-Penetrating Radar: Ground-penetrating radar is a time scaled
system. The system measures the time it takes electromagnetic
energy to travel from an antenna to an interface (i.e., soil
horizon, stratigraphic layer) and back. To convert travel time into
a depth scale requires knowledge of the velocity of pulse
propagation. Several methods are available to determine the
velocity of propagation. These methods include use of table
values,
1 Manufacturer's names are provided for specific information;
use does not constitute endorsement.
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2
common midpoint calibration, and calibration over a target of
known depth. The last method is considered the most direct and
accurate method to estimate propagation velocity (Conyers and
Goodman, 1997). The procedure involves measuring the two-way travel
time to a known reflector that appears on a radar record and
calculating the propagation velocity by using the following
equation (after Morey, 1974):
V = 2D/T [1] Equation [1] describes the relationship between the
propagation velocity (V), depth (D), and two-way pulse travel time
(T) to a subsurface reflector. During this study, the two-way radar
pulse travel time was compared with measured depths to known
subsurface interfaces within each study site. Computed propagation
velocities were used to scale the radar records. Electromagnetic
Induction: Electromagnetic induction is a noninvasive geophysical
tool that can be used for soil and site investigations. Advantages
of EMI are its portability, speed of operation, flexible
observation depths, and moderate resolution of subsurface features.
Results of EMI surveys are interpretable in the field. This
geophysical method can provide in a relatively short time the large
number of observations that are needed to comprehensively cover
sites. Maps prepared from correctly interpreted EMI data provide
the basis for assessing site conditions, planning further
investigations, and locating sampling or monitoring sites.
Electromagnetic induction uses electromagnetic energy to measure
the apparent conductivity of earthen materials. Apparent
conductivity is a weighted, average conductivity measurement for a
column of earthen materials to a specific depth (Greenhouse and
Slaine, 1983). Variations in apparent conductivity are caused by
changes in the electrical conductivity of earthen materials. The
electrical conductivity of soils is influenced by the type and
concentration of ions in solution, volumetric water content,
temperature and phase of the soil water, and amount and type of
clays in the soil matrix (McNeill, 1980). The apparent conductivity
of soils increases with increases in soluble salts, water, and clay
contents (Kachanoski et al., 1988; Rhoades et al., 1976).
Electromagnetic induction measures vertical and lateral variations
in apparent electrical conductivity. Values of apparent
conductivity are seldom diagnostic in themselves. However, relative
values and lateral and vertical variations in apparent conductivity
can be used to infer changes in soils and soil properties.
Interpretations are based on the identification of spatial patterns
within data sets. To assist interpretations, computer simulations
of EMI data are normally used. To verify interpretations,
ground-truth measurements are required. Discussion The MLRA soils
office located in Laurens, SC has a newly acquired conductivity
meter (Profiler EMP-400 manufactured by Geophysical Survey Systems,
Inc., Nashua, NH). Apparent conductivity surveys were completed at
multiple sites as associations were made between changes in
apparent conductivity (ECa) and changes in soil properties
including depth to bedrock and changes in clay and moisture.
Ground-penetrating radar surveys were also completed to assess
changes in depth to bedrock and associated changes in apparent
conductivity. Site 1 EMI Survey – Dairy Site (Laurens County) Soils
The site is located approximately 3 miles northeast of the small
town of Gray Court, SC. The site was in an area mapped Appling
loamy sand, 2 to 6 percent slopes and Appling loamy sand, 6 to 10
percent slopes
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3
(USDA/NRCS, Web Soil Survey). Field 2 was mapped Cecil sandy
loam, 2 to 6 percent slopes and Cecil sandy loam, 6 to 10 percent
slopes, eroded. The very deep, well drained Appling and Cecil soils
formed on ridges and side slopes of the Piedmont uplands in
residuum weathered from felsic igneous and metamorphic rocks. These
soils are deep to saprolite and very deep to bedrock. Soil
Classification - Site 1 (Laurens County) and Site 2 (Chester/York
Counties) Appling - fine, kaolinitic, thermic Typic Kanhapludults
Cecil - fine, kaolinitic, thermic Typic Kanhapludults Thomson -
coarse-loamy, mixed, semiactive, thermic Ultic Hapludalfs Molena -
mixed, thermic Psammentic Hapludults Brewback - fine, mixed,
active, thermic Aquertic Hapludalfs Wynott - fine, mixed, active,
thermic Typic Hapludalfs Winnsboro - fine, mixed, active, thermic
Typic Hapludalfs Chewacla - fine-loamy, mixed, active, thermic
Fluvaquentic Dystrudepts Survey Design: Two individual surveys were
completed to assess the survey site (Figure 1). The grid area was
approximately 200 meters x 130 meters. Survey procedures were
simplified to expedite fieldwork. Two parallel lines defined the
upper and lower boundaries of each survey grid area. EMI surveys
were completed by walking at a fairly uniform pace in a back and
forth pattern. Survey transect lines were spaced apart at a
distance of 20 meters. The Profiler was carried at a height of
approximately 8 inches (20 cm) above the surface and was operated
in the continuous mode with measurements recorded at a 1 sec
interval. The meter was carried in the vertical and the horizontal
dipole orientations during data collection in two separate surveys.
Depth of penetration (geometrical) was approximately 0 - 1.8 meters
in the vertical orientation and 0.9 meters in the horizontal dipole
orientation.
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4
Photo 1. EMI survey completed with the Profiler EMP-400 sensor,
manufactured by Geophysical Survey Systems, Inc., Nashua, NH.
Measurements of apparent conductivity are measured in milliSiemens
per meter (mS/m). The soils staff located in Laurens, SC did an
excellent job operating and processing the ECa data resulting from
the EMI surveys.
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5
-82.0795 -82.079 -82.0785 -82.078 -82.0775
34.641
34.6415
34.642
34.6425
Dairy SiteVertical Dipole Orientation
(0 - 1.8 m)
-82.0795 -82.079 -82.0785 -82.078 -82.0775
34.641
34.6415
34.642
34.6425
-82.0795 -82.079 -82.0785 -82.078 -82.0775
34.641
34.6415
34.642
34.6425
-82.0795 -82.079 -82.0785 -82.078 -82.0775
34.641
34.6415
34.642
34.6425
-82.0795 -82.079 -82.0785 -82.078 -82.0775
34.641
34.6415
34.642
34.6425
-55-51-47-43-39-35-31-27-23-19-15-11-7-315913172125293337
Latit
ude
Longitude
mS/m
-82.0795 -82.079 -82.0785 -82.078 -82.0775
34.641
34.6415
34.642
34.6425
Dairy SiteHorizontal Dipole Orientation
(0 - 0.9 m)
0246810121416182022242628303234363840
-82.0795 -82.079 -82.0785 -82.078 -82.0775
34.641
34.6415
34.642
34.6425
-82.0795 -82.079 -82.0785 -82.078 -82.0775
34.641
34.6415
34.642
34.6425
Longitude
Latit
ude
mS/m
B
A
C
C
C
C
C
C
CC
C
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6
Figure 1. Spatial pattern of apparent conductivity (ECa)
measured with the GSSI Profiler conductivity meter in an area
mapped Appling loamy sand, 2 to 6 percent slopes and Appling loamy
sand, 6 to 10 percent slopes. The anomalous spikes in apparent
conductivity (locations C) are thought to be attributed to
discarded metal debris. Results Figure 1. A total of 1011
measurements were recorded with the GSSI Profiler meter in the
horizontal dipole orientation (HDO). Apparent conductivity averaged
5.4 mS/m and ranged from 0.2 to 41.6 mS/m. One-half of the
observations had an apparent conductivity between 3.9 and 5.9 mS/m.
A total of 983 measurements were recorded with the GSSI Profiler
meter in the vertical dipole orientation (VDO). Apparent
conductivity averaged 4.0 mS/m and ranged from -79.1 to 15.2 mS/m.
One-half of the observations had an apparent conductivity between
3.5 and 6.2 mS/m.
Figure 2. Spatial pattern of apparent conductivity (ECa)
measured with the GSSI Profiler conductivity meter in an area
mapped Cecil sandy loam, 2 to 6 percent slopes and Cecil sandy
loam, 6 to 10 percent slopes, eroded.
-82.083 -82.0825 -82.082 -82.0815 -82.081 -82.0805
34.6395
34.64
34.6405
34.641
-82.083 -82.0825 -82.082 -82.0815 -82.081 -82.0805
34.6395
34.64
34.6405
34.641
1.5
3.5
5.5
7.5
9.5
11.5
Field 2 - Dairy SiteVertical Dipole Orientation
(0 - 1.8 m)mS/m
-82.083 -82.0825 -82.082 -82.0815 -82.081 -82.0805
34.6395
34.64
34.6405
34.641
Latit
ude
Longitude
A
B
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7
Results Figure 2. A total of 1697 measurements were recorded
with the GSSI Profiler meter in the vertical dipole orientation
(VDO). Apparent conductivity averaged 8.3 mS/m and ranged from -2.1
to 13.0 mS/m. One-half of the observations had an apparent
conductivity between 7.6 and 9.1 mS/m.
Photo 2. Soil borings are being taken after an EMI survey with
the Profiler to verify changes in apparent conductivity and
associated changes in soil properties. In Figures 1 and 2, changes
in spatial patterns of apparent conductivity were thought to be
associated with changes in soil characteristics. Areas containing
higher apparent conductivity were thought to contain more
clay/moisture and/or deeper soil profiles. In Figure 1, the
soil/bedrock interface was observed in soil borings at 73 cm (29
in.) at location “A” and 33 cm (13in.) at location “B”. In Figure
2, soil borings at location “A” revealed a more developed soil
profile with a thicker clay subsoil horizon - 95 cm (38 in) and no
soil/bedrock interface was observed within 1.5 m (60 in.). Soil
borings at location “B” revealed a thinner clay subsoil horizon
thickness - 50 cm (20 in.) and a soil/bedrock interface observed at
115 cm (46 in.). More contrasting anomalous features (spikes in
apparent conductivity – areas “C”) were thought to be associated
with discarded metallic objects (Figure 1). Metal debris was
observed across the survey area at various locations.
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8
Soils across the survey area (Figure 1) were mapped Appling
loamy sand, 2 to 6 percent slopes and Appling loamy sand, 6 to 10
percent slopes and are classified as very deep to bedrock. Soil
borings and observations at various locations across the survey
area suggest that shallower soils dominate the site. Moderately
deep (50 -100 cm) and shallow soils (
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9
Figure 3. File 13. Radar record collected with the SIR-3000
radar unit and a 200 MHz antenna across an area of Cecil sandy
loam, 6 to 10 percent slopes, eroded. A white line approximates the
soil/bedrock interface. Scale is in meters.
Figure 4. File 14. Radar record collected with the SIR-3000
radar unit and a 200 MHz antenna across an area of Cecil sandy
loam, 2 to 6 percent slopes. A black line approximates the
soil/bedrock interface. Scale is in meters.
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10
Radar records obtained with the 200 MHz antenna was generally of
good to excellent interpretative quality. Observation depths were
greater than 2.0 meters. After review of the radar records and
associated ground-truthing (soil borings), soils across the survey
transect area ranged from shallow to moderately deep to very deep
and were quite variable with respect to depth to bedrock. The soils
across the survey site were mapped very deep. Interpretative
results suggest a complex of soils with respect to soil depth.
Additional investigations need to be completed to more fully assess
map unit composition. Site 2 - Chester/York Counties EMI Surveys
Soils The sites are located approximately 3 miles (Figure 5) and
3.5 miles (Figure 6) north of the community of Lockhart, SC near
the Chester and York County line. Site 2A was in an area mapped
Thomson sandy loam, 0 to 4 percent slopes and Molena.variant sand,
1 to 4 percent slopes. Site 2B was in an area mapped Brewback fine
sandy loam, 2 to 6 percent slopes, Cecil sandy clay loam, 2 to 6
percent slopes, moderately eroded, Wynott-Winnsboro complex, 6 to
10 percent slopes, moderately eroded and Chewacla loam, 0 to 2
percent slopes, frequently flooded (USDA/NRCS, Web Soil Survey).
The very deep, well drained Thomson soils formed in loamy and sandy
fluvial sediments on Piedmont stream terraces and flood plains. The
moderately deep, somewhat poorly drained Brewback soils formed in
residuum from basic rocks or mixed acid and basic rocks on Piedmont
uplands. The very deep, somewhat excessively drained Molena soils
formed on stream terraces of the Piedmont and have reddish brown
sand A horizons, and yellowish red loamy fine sand Bt horizons. The
moderately deep, well drained Wynott soils formed in residuum from
gabbro, diorite, and other dark colored mafic rocks on uplands in
the Piedmont. The deep, well drained fine Winnsboro soils that
formed in material mostly weathered from dark colored basic rocks
of the Piedmont. The very deep, somewhat poorly drained Chewacla
soils formed on alluvial flood plains in the Piedmont and Coastal
Plain regions. Survey Design: Surveys were completed to assess the
survey sites (Figures 5 and 6). The survey areas were irregular in
size and shape. Survey procedures were simplified to expedite
fieldwork. Two semi-parallel lines defined the eastern and western
boundaries of each survey grid area. EMI surveys were completed by
walking at a fairly uniform pace in a back and forth pattern while
methodically traversing the sites while collecting apparent
conductivity measurements. The Profiler was carried at a height of
approximately 8 inches (20 cm) above the surface and was operated
in the continuous mode with measurements recorded at a 1 sec
interval. The meter was carried in the vertical dipole orientation
(VDO) during data collection at the two separate sites. Depth of
penetration (geometrical) was approximately 0 - 1.8 meters in the
vertical dipole orientation.
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11
Figure 5. Spatial pattern of apparent conductivity (ECa)
measured with the GSSI Profiler conductivity meter in an area of
Thomson sandy loam, 0 to 4 percent slopes and Molena.variant sand,
1 to 4 percent slopes. Site 2A - Results – Figure 5 A total of 2570
measurements were recorded with the GSSI Profiler meter in the
vertical dipole orientation (VDO). Apparent conductivity averaged
5.9 mS/m and ranged from -86.8 to 255.0 mS/m. One-half of the
observations had an apparent conductivity between 3.6 and 7.0 mS/m.
In Figure 5, changes in spatial patterns of apparent conductivity
were thought to be associated with changes in soil characteristics
as observed in soil borings at locations A, B and C. Areas
containing higher apparent conductivity (B) contained more
clay/moisture as compared to soil profiles observed at locations A
and C. Anomalous spikes in apparent conductivity (locations D) were
thought to be associated with discarded metal debris. The elevated
spike in apparent conductivity at location E was thought to be
attributed to the close proximity to the metal wire fence line.
-81.4565 -81.456 -81.4555 -81.455 -81.4545 -81.454
34.822
34.8225
34.823
34.8235
Field 1Profiler - Vertical Dipole Orientation
(0 - 1.8 m)
-81.4565 -81.456 -81.4555 -81.455 -81.4545 -81.454
34.822
34.8225
34.823
34.8235
0
4
8
12
16
20
24
28
-81.4565 -81.456 -81.4555 -81.455 -81.4545 -81.454
34.822
34.8225
34.823
34.8235mS/m
Latit
ude
Longitude
A
BC
E
D
D
D
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12
Site 2B – Field 2 (back side of farm) Results – Figure 6 A total
of 975 measurements were recorded with the GSSI Profiler meter in
the vertical dipole orientation (VDO). Apparent conductivity
averaged 19.8 mS/m and ranged from 5.5 to 43.9 mS/m. One-half of
the observations had an apparent conductivity between 14.0 and 24.8
mS/m. In Figure 6, changes in spatial patterns of apparent
conductivity were thought to be associated with changes in soil
characteristics as observed in soil borings. This was also
reflected in soils mapping at the site. The higher activity clays
with higher expansive properties observed in the Brewback soils
attributed to higher apparent conductivity as compared to the lower
activity clays observed in the adjacent Cecil soils. Geophysical
interpretations are considered preliminary estimates of site
conditions. The results of all geophysical investigations are
interpretive and do not substitute for direct soil borings. The use
of geophysical methods can reduce the number of soil observations,
direct their placement, and supplement their interpretations.
Interpretations should be verified by ground-truth
observations.
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13
-81.4494 -81.449 -81.4486
34.833
34.8332
34.8334
34.8336
34.8338
34.834
34.8342
34.8344
34.8346
34.8348
34.835
34.8352
Field 2 - (backside of farm)Profiler - Vertical Dipole
Orientation
(0 - 1.8 m)mS/m
-81.4494 -81.449 -81.4486
34.833
34.8332
34.8334
34.8336
34.8338
34.834
34.8342
34.8344
34.8346
34.8348
34.835
34.8352
-81.4494 -81.449 -81.4486
34.833
34.8332
34.8334
34.8336
34.8338
34.834
34.8342
34.8344
34.8346
34.8348
34.835
34.8352
4
9
14
19
24
29
34
39
44
Latit
ude
Longitude
Brewback fsl, 2-6%
Cecil scl, 2-6 %,mod. eroded
Wynott-Winnsboro complex, 6-10%, mod. eroded
Chewacla loam, 0-2%, freq. flooded
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14
Figure 6. Spatial pattern of apparent conductivity (ECa)
measured with the GSSI Profiler conductivity meter in an area of
Brewback fine sandy loam, 2 to 6 percent slopes, Cecil sandy clay
loam, 2 to 6 percent slopes, moderately eroded, Wynott-Winnsboro
complex, 6 to 10 percent slopes, moderately eroded and Chewacla
loam, 0 to 2 percent slopes, frequently flooded. References:
Conyers, L. B., and D. Goodman. 1997. Ground-penetrating Radar; an
introduction for archaeologists. AltaMira Press, Walnut Creek, CA.
232 pp. Daniels, D. J. 1996. Surface-Penetrating Radar. The
Institute of Electrical Engineers, London, United Kingdom.
Doolittle, J. A. 1987. Using ground-penetrating radar to increase
the quality and efficiency of soil surveys. 11-32 pp. In: Reybold,
W. U. and G. W. Peterson (eds.) Soil Survey Techniques, Soil
Science Society of America. Special Publication No. 20. Geonics
Limited. 1998. EM38 ground conductivity meter operating manual.
Geonics Ltd., Mississauga, Ontario. Greenhouse, J. P., and D. D.
Slaine. 1983. The use of reconnaissance electromagnetic methods to
map contaminant migration. Ground Water Monitoring Review 3(2):
47-59. Kachanoski, R. G., E. G. Gregorich, and I. J. van
Wesenbeeck. 1988. Estimating spatial variations of soil water
content using noncontacting electromagnetic inductive methods. Can.
J. Soil Sci. 68:715-722. McNeill, J. D. 1980. Electromagnetic
terrain conductivity measurement at low induction numbers.
Technical Note TN-6. Geonics Ltd., Mississauga, Ontario. Morey, R.
M. 1974. Continuous subsurface profiling by impulse radar. p.
212-232. IN: Proceedings, ASCE Engineering Foundation Conference on
Subsurface Exploration for Underground Excavations and Heavy
Construction, held at Henniker, New Hampshire. Aug. 11-16, 1974.
Rhoades, J. D., P. A. Raats, and R. J. Prather. 1976. Effects of
liquid-phase electrical conductivity, water content, and surface
conductivity on bulk soil electrical conductivity. Soil Sci. Soc.
Am. J. 40:651-655. USDA/NRCS, Web Soil Survey
(http://websoilsurvey.nrcs.usda.gov/app
Geonics Limited. 1998. EM38 ground conductivity meter operating
manual. Geonics Ltd., Mississauga, Ontario.
2016-08-29T16:52:04-0500DAVID HOOVER