17th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems

Recent advances in apparent soil electrical conductivity (ECa) sensor technology have provided
the opportunity to rapidly map the nature of soil spatial variability for purposes of agricultural sitespecific
management. A better understanding of the temporal and spatial variability of ECa is needed to
enhance its practical utility in agriculture. In this article, we summarize our recent studies that utilized
multi-year measurements of field-scale ECa and soil profile properties in three non-saline and irrigated
sandy fields in eastern Colorado. The objectives were to quantify the degree of temporal change in ECa
patterns across the fields and to identify the main soil properties that alter ECa values. Results show that
in the sandy and non-saline fields examined in this study, delineated ECa patterns into low, medium, and
high zones remained largely unchanged between 1998 and 2002, even though the absolute values of ECa
varied. When salt concentration and buildup is low (as was the case herein), results suggest single ECa
mapping should suffice to delineate stable ECa zones without a need for remapping. In all three fields,
ECa was found to be a strong linear function of soil water content, clay, CEC, and organic matter
contents with correlation coefficients ranging between 0.75 and 0.94. In spite of the strong correlations
between ECa and soil properties at each given measurement day, there was no single unique relationship
applicable across all measurement days.

Key components of precision agriculture are (i) identifying the site-specific factors that influence
within-field crop yield variation and (ii) spatially characterizing those factors. Geo-referenced
measurements of apparent soil electrical conductivity (ECa) provide a potential means of characterizing
the spatial variability of edaphic properties that influence crop yield. It is the objective (i) to utilize an
intensive ECa survey to direct soil sampling, (ii) to identify soil properties that influence cotton yield,
and (iii) to use this spatial information to make site-specific management recommendations to increase
cotton yield. A 32.4-ha field in California’s San Joaquin Valley was used as a study site. Cotton yield
monitoring data were collected in August 1999 followed by an intensive ECa survey of 4000+
measurements using electrical resistivity. Sixty soil sample sites were selected based upon a responsesurface
sampling design utilizing the spatial ECa measurements. Scatter plots were obtained and
correlation and regression analyses were performed to assess the relationship between cotton yield and
the properties of pH, boron (B), nitrate-nitrogen (NO3-N), chloride (Cl-), salinity (i.e., electrical
conductivity of the saturation extract; ECe), leaching fraction (LF), water content (θg), bulk density (ρb),
% clay, and saturation percentage (SP). Correlation coefficients of -0.01, 0.50, -0.03, 0.25, 0.53, -0.49,
0.42, -0.29, 0.36, and 0.38, respectively, were found. The correlation coefficient between yield and ECa
was 0.51. A site-specific response model of cotton yield based on ordinary least squares (OLS) and
adjusted for spatial autocorrelation using restricted maximum likelihood was developed. The response
model indicated that leaching fraction, salinity, water content, and pH were the most significant soil
properties influencing cotton yield: cotton yield (Mg ha-1) = 19.28 + 0.22 ECe – 0.02 ECe
2 – 4.42 LF2 –
1.99 pH + 6.93 θg. The spatial information and response model provide sufficient information to make
site-specific management recommendations to increase cotton yield.

Enhancing the efficiency of soil water removal on land already containing a subsurface drainage
system typically involves installing new drain lines between the old ones. However, before this
approach can be attempted, the older drainage pipes need to be located. In ongoing research, ground
penetrating radar (GPR) has been successful in locating on average 72% of the total amount of drainage
pipe present at thirteen test plots in southwest, central, and northwest Ohio. The effective use of GPR
for drainage pipe detection requires careful consideration of computer processing procedures, equipment
parameters, and site conditions, all of which were thoroughly investigated in this study.
Application of a signal saturation correction filter along with a spreading and exponential
compensation gain function were the computer processing steps most helpful for enhancing the drainage
pipe response exhibited within GPR images of the soil profile. GPR amplitude maps that show the
overall subsurface drainage pipe system required additional computer processing, which included 2-D
migration, signal trace enveloping, and in some cases, a high frequency noise filter and a spatial
background subtraction filter. Equipment parameter test results indicate that a 250 MHz antenna
frequency worked best, and that data quality is good over a range of spatial sampling intervals and signal
trace stacking. In regard to the site conditions present, shallow hydrology, soil texture, and drainage
pipe orientation all substantially influence the GPR response. However, the fired clay or plastic material
of which the drainage pipe is comprised does not appear to have much of an impact. The information
supplied by this study can be employed to formulate guidelines that will enhance the potential of success
for using ground penetrating radar in locating buried agricultural drainage pipe.

For a variety of applications, magnetic data is collected from airborne platforms. Normally, this
data is collected with sensors that measure the total field or amplitude of the magnetic vector data. New
generations of optically pumped sensors are extremely sensitive with their sensitivity quoted often in
picoteslas. At present, some new instrumentation is also attempting to measure high accuracy vector
data. Despite the accuracy of modern sensors and data acquisition systems, the noise of the flying
platform is still one of the limiting factors in obtaining highly accurate data.
The aircraft or helicopter itself emanates magnetic signals. These signals are due to a number of
factors including induced fields due to magnetically susceptible materials and permanent magnetic
materials on the platforms as well as both induced electromagnetic signals and electromagnetic signals
generated either by electrical systems or moving parts such as rotors.
This subject of this paper are problems and techniques related to removing the effects of the
moving platform as well as attempts to study the subject with the use of simulated data.

The Island of Vulcano belongs to the active Eolian volcanic arc. Recent events on Stromboli
have renewed public interest and consciousness about this type of natural hazard not only in Italy, but
almost in the whole of Europe. A strong need for a reliable method to recognise significant changes in
the internal state of a volcano has risen, because of the currently ongoing and permanently changing
activity of the Eolian volcanic system. The measurement of variations in the local total magnetic field
anomaly within repeated airborne surveys is a promising strategy since rocks loose their magnetisation
when they are heated to temperatures higher than the so-called Curie-point resulting in a decline within
anomalies in the local magnetic field. Thus, changes in the geomagnetic field can indicate changes in the
dynamical behaviour of the geothermal volcanic system. Two airborne magnetic surveys have been
conducted by the Geological Survey of Austria in 1999 and in 2002 in the area of Vulcano and over a
part of Lipari. The raw data have to be carefully processed in order to be comparable, since they have
been assembled at different altitudes. Sophisticated innovative field transformation algorithms had to be
developed, and the rough topography and high susceptibility of the island of Vulcano require a
topographic correction of the measured data. Preliminary results, however, exhibit some significant
changes in the magnetic anomaly field.

A helicopter electromagnetic and magnetic (HEM) survey has been done as part of an abandoned
mine land study. An important aspect of this study is to estimate ground water flow paths in the surface
and subsurface (bedrock). The apparent conductivity and total field magnetic maps from the HEM
survey are used to identify geologic features that can influence ground water flow. The most easily
understood studied ground water flow paths are near surface streams and flow through alluvial or
colluvial deposits. The HEM data indicates parts of the upper Animas River where bedrock ground
water flow may be important. Interestingly the other two major drainages (Cement and Mineral Creek)
are not associated with geophysical responses that indicate deep structures. High apparent conductivities
near one mine waste pile suggest near surface flow paths and a source for high dissolved solids where
high sulfide mill tailings have been removed after the HEM survey. The youngest dacite-rhyolite
intrusives show different types of magnetic and electrical properties that may have implications for the
occurrence of acid generating lithologies. Apparent conductivity maps suggest a northwest trending
structural zone along Cement creek that may control ground water flow. Total field magnetic data
suggest northwest trending structures that cross the Silverton Caldera ring fracture system.

Tel Yavne in Israel is the site of the ancient city of Yavne. Located about 20 kilometers south of
Tel Aviv, and about 8 km inland from the ancient seaport of Yavne Yam (meaning Yavne by the Sea), it
is believed that underneath the tel (an archaeological mound) are the remains of more than 3,000 years
of continuous occupation. The tel, at 4 hectares in area and approximately 30 m in elevation, is
relatively large in comparison to other ancient sites in Israel. To date, no excavations have been carried
out at the site. In preparation for excavation work at a later date, electrical resistivity tomography (ERT)
surveys, ground penetrating radar surveys, and low altitude photography from kites and balloons were
carried out at the site. This paper will discuss the ERT and photographic surveys. The objectives of
these two surveys were to delineate the plan view and vertical extent of accumulated cultural debris, and
to identify particular areas for initial test pitting by archaeologists. Eight ERT cross-sections were
imaged, ranging in length from 80 to 140 m. Approximately 500 low altitude photographs were shot.
Specific features possibly identified include a 9th century B.C.E. (before the common era) water system,
the Philistine city wall dating from 790 B.C.E., the ruins of a 12th century C.E. Crusader castle, and
numerous architectural features from the Mameluke, Ottoman, and Palestinian periods of habitation.
This is the first time that non-destructive techniques have been used in the first phase of an
archaeological exploration program in Israel at such an important, well recognised ancient site.

Several types of circular burial tombs, built by different populations in different ages, can be
discovered in Europe and have in common only their location inside small hills in the countryside.
These mounds have lateral dimensions varying from few meters to tens of meters, and heights around 5-
10 meters. Since the standard geophysical mapping measurements used by archaeologists are not well
suited for such targets under complex topography, a method that allows accurate image reconstructions
in 3D is required.
Different kind of mounds have been analyzed in this work: Etruscan (pre-Roman) burial sites,
very common in central Italy, and Celtic "Princes Age" (VI century b. C.) tombs in the Western Alps,
similar to sites excavated in the ’70s in southern Germany, that provide a good experimental set for the
variety of dimensions and materials used. The wood posts and stone walls surrounded by clay trenches
used in Celtic tombs create strong resistivity contrasts, while weaker anomalies are found over Etruscan
tombs.
The paper describes the development of a specific DC measurements on electrode grids placed
over the whole surface of the mounds, that provide realistic 3D pictures meant to guide drilling or
excavation and avoid collaptions. The use of fast multi-channel instruments allows the collection of
many data points in different array configurations, while data is processed using a 3D FEM modelling
and inversion routine that allows to input complex topographic information.

Geophysical surveys were conducted at culturally sensitive sites in the New Madrid seismic zone
(NMSZ) of the central United States to locate buried earthquake-induced liquefaction deposits for
paleoseismic study. Although recent seismicity of the zone is of low to moderate magnitude, studies of
prehistoric earthquake sequences suggest that very large earthquakes occurred in A.D. 900 ± 100 years
and A.D. 1450 ± 150 years, in addition to the well-known historic events of 1811-1812 that caused
widespread soil liquefaction in Mississippi Valley alluvial deposits. Dates for the prehistoric
earthquakes are derived from radiocarbon dating of charcoal and from the presence of Native American
cultural features and artifacts of distinct periods that are collocated with buried liquefaction features,
such as sand fissures and sand blows. Trench excavations are often necessary to establish stratigraphic
and structural relationships critical for determining the timing of these paleoliquefaction events. Because
many sites are located in culturally sensitive or federally protected areas, non-invasive methods that can
increase the likelihood of identifying potential excavation sites while minimizing destruction of the site
are highly desirable. Geophysical surveys conducted at numerous sites in the NMSZ demonstrate that
subsurface imaging techniques can be useful for siting trenches for paleoseismic study and for
identifying areas susceptible to liquefaction.

Two Borehole Ground Penetrating Radar (GPR) surveys were conducted to evaluate
fractured limestone bedrock formations. One survey was conducted at the proposed location for
a bridge pylon and one at a limestone quarry. The objective for both surveys was to identify
small voids and fractures in the limestone. At the proposed pylon site, the voids and fractures
were mapped to evaluate the limestone’s bearing capacity and to design a grouting program. At
the quarry site, the voids and fractures were mapped to help identifying permeable layers.
Borehole GPR is the only geophysical technique capable of imaging individual small voids and
fractures that do not intersect a borehole. A MALA Geoscience borehole GPR tool configured
with 250 and 100 MHz antennas was employed for these investigations.
Nine boreholes were drilled into the limestone formation at the footprint of the proposed
pylon. All nine boreholes were surveyed in reflection mode using 100 MHz and 250 MHz
borehole GPR antennas. Two cross-hole tomographic surveys were also conducted at the site.
The reflection surveys identified multiple layers that indicated voids and fractures of varying intensity.
The tomography data provided information regarding the bulk characteristics of geological units
and identified smaller areas with anomalous high porosity that could indicate high density of voids or
fractures.