Past, present a nd future of soil investigation using [616330]

Past, present a nd future of soil investigation using
geophysical methods

CONSTANTINESCU LAVINIA
University of Bucharest, Faculty of Geology and Geophysics,
Department of Geophysics, 6 Traian Vuia S t., 020956 Bucharest,
Romania,
e-mail: [anonimizat]

Abstract—Geophysical methods are often used to
characterize the soil properties of the subsurface, their
main advantage being the non -invasive nature, portraying
the possibi lity of qualitative and quantitative data
interpretation.
This review proves the geophysics method ’s
effectiveness and strongly support s its usage in the future
studies of soil investigation.

Keywords —pedometrics, geophysical methods, soil
investigation s;
I. INTRODUCTION
Geophysics represents the application of physical
principles to studies of the Earth (Sheriff, 2002).
This is a general definition of geophysics and is
related to a wide range of disciplines such as: oil and
gas exploration, exploration of mineral resources,
geotechnical engineering, hydrogeology ,
environmental studies, archaeology, agriculture, etc.
Even since the A.D 132 year when one of the
first known instrument for geophysical measurement
was invented, respectively the seismoscope ,
geophysical instruments and techniques evolved in
time, now being available a lot of modern sensors
and tools with investigation depths varying from
some centimeters to hundreds of kilometers.
In soil investigation applications, the most used
geophysical t echniques are resistivity methods ,
electromagnetic induction, ground -penetrating radar,
magnetometry, self -potential and seismics (Table 1) . TABLE I. PHYSICAL PROPERTIES RESPONDED TO BY GEOPHYSICAL
METHODS
Geophysical Method Physical Property

Resistivity Electr ical resistivity (electrical
conductivity)
Electromagnetic induction Electrical conductivity (electrical
resistivity)
Ground Penetrating Radar Dielectric constant and electrical
conductivity
Magnetic methods Magnetic susceptibility and
remanent magnetis m
Self Potential Electric potential gradient
Seismic Density and elastic moduli (bulk
modulus, shear modulus, etc.)

II. GEOPHYSICAL METHODS A S A TOOL IN
PEDOMETRICS AND SOIL RESEARCH
Currently , there are many types of classifications
which are grou p soils by their intrinsic property (soil
morphology), genesis, parent material or behavior
(e.g. FAO Soil Classification, Australian Soil
Classification, French soil classification, USDA soil
taxonomy, AASHTO Soil Classification System,
etc). A good estimation of soil parameters is
extremely important to determinate soil properties
and understanding soil distribution patterns.
Conventional soil survey methods, used to be
criticized in the past, perhaps justifiably so , being to
qualitative in character. As a respo nse to this
criticism in last 30 years quantitative methods have
been developed, which enable precise estimation of
soil parameters and spatial distribution patterns of

soils. This methods are also known as pedometrics.
Pedometrics originates from the Gree k roots
(“pedos” = soil and “metrics” = measuring) and
represents the application of mathematical and
statistical methods for the study of the distribution
and soil genesis. Even if pedometrics is not new
(mathematical and statistical methods have been
used in soil studies since 1960’s), it was recognized
as a different branch of soil science just a decade
ago.
Geophysical methods (on ground surface or air –
borne) represent the most important noninvasive
techniques used for soil investigation. Th ese soil-
measuring systems are in present very commonly
used because of their advantages like high precision,
their efficient usage and also simplicity.

III. GEOPHYSICAL METHODS USED FOR SOIL
INVESTIGATION

The applicability of geophysical methods in soil
investigati on surveys can be summarized as follows.

A. Magnetic method s:

Magnetic method is one of the most used
geophysical technique in soil investigation,
especially becau se all soils types have more or less,
a magnetic response. Properties such as magnetic
viscos ity (K qu) and magnetic susceptibility (K ph) of
soils, are mostly linked to the iron oxides and
hydroxides amount contained by soils and also about
their disposal and grain size. Iron oxides in soils are
mostly generated in reduction environments but also
by some bacterial activities. While the original
pattern of soils has constant magnetic properties,
human activity tends to increase the iron oxides
content, resulting higher magnetic contrasts between
undisturbed soils and anthropogenic disturbed soils.
In last century, a lot of scientist proved the usage
of this particular geophysical tool for soil
investigation, in various studies such as the
anthropogenic contamination by heavy metals of
soils, archaeology, agriculture or mineral
exploration. Examples of soil pollution with heavy
metals are represented by studies developed in China, Xuzhou town (Xuesong Wang, 2013), in
Romania, Bucharest town (Panaiotu et. a l, 2011), in
Poland , Lublin town (A. Alekseev et. all, 2002), etc.
Such studies demonstrates a good correlation
between heavy metals (Zn, Pb, Fe, Mn, Cu, Cd, Sr
and Ba) and high magnetic susceptibility values
measured in anthropogenic soils. Other examples of
magnetic methods successfully application are
represented by detect ion of old pipes and metalli c
structures, especially where soils have a high clay
content and GPR method can’t be applied (Rogers et
al., 2005, Rogers et. al.,2006).

B. Resistivity methods :

A lot of experimental works have demonstrated
the inverse proportionality between the electric al
resistivity and the water content of soils (Kalinski &
Kelly, 1993), electrical resistivity investigation of
soils being one of the most used method for water
detection zones.
The resistivity technique originates from 1920s
due to Schlumberger brothers work and was
normally developed for hydrocarbons exploration.
Since then, this method has known a wide usage ,
currently it is being used in a lot of soil applications
such as agriculture, archaeology, hydrogeology and
environmental studies. Such studies i nclude the use
of apparent resistivity techniques in agricultural
pollution with fertilizers and pesticides (Christensen
and Sorensen 1993), in scope of detecting old
industrial materials (Barker,1996), in scope of
detecting holes or non -compacted soil cla y layers
(Loke and Barker, 1996), in scope of detecting water
infiltrations or pollutants leakage from dams (Baker
and Moore, 1998, Johansson and Dahlin 1996), in
archaeology studies such as detection of buried
walls (Urbini et. al., 2007), etc.

C. EMI meth ods:

Electromagnetic induction (EMI) is a very
common geophysical method used by soil scientists
to understand a better spatial variability of soils and
soil properties (Corwin, 2008, Toushmalani, 2010).

Electromagnetic induction techniques measure
chang es in electrical conductivity (or resistivity),
without a direct contact between sensor and soil
surface like in DC resistivity techniques. Apparent
conductivity of soils is normally increased by high
soluble salt content, high amount of water, high clay
content and high temperature. In soil investigation,
this method has numerous applications in
agriculture, since 1982, in archaeology, soil
pollution and environmental studies, hydrogeology
and geotechnical studies.
If in the past, EMI surveys were complet ed with
EMI sensors across gridded areas, now these sensors
are operated in the station -to-station mode without a
data logger. Also, new EMI meters have GPS
systems incorporated and can register in continuous
recording mode. Examples of studies using EMI
induction method are given by McNeill, 1980,
Heilig et al.,2011 which described apparent
conductivity as a good indicator of soil properties
such as soil matrix, phase of the soil water, bulk
density, soil structure, ionic composition, pH, soil
organic carb on, nutrients and CaCO3. In agriculture
applications, geotechnical studies and hydrogeology
of soil investigation, EMI method has been proved
to be extremely helpful for measuring spatial
variability of soil properties at field and landscape
scales, such ex amples are given by Corwin, 2008,
Luck et al .,2009) .

Figure. 3D model showing spatial distribution of apparent
electrical conductivity of soil in a filed from North Dakota
(Heilig et a l., 2011).
D. GPR methods:

Ground Penetrating Radar (GP R or Ground
Radar) was originally developed for mapping
geological features, now being increasingly used in
soil investigations, geotechnical engineering,
constructions, roads, runways, hazardous waste,
archaeology and many other applications. The most
significant influences in investigation depth of GPR
method are given by antenna frequency, highly
conductive features such as clay soils, soils
contaminated with salt and the amount of iron oxide.
GPR method is based on the electromagnetic
waves propagation , the principle actually being very
similar to seismic reflection technique. The
propagation of electromagnetic waves is governed
by Maxwell’s equations, wave’s velocity and energy
attenuation, both being affected mostly by relative
magnetic permeability ( generally negligible) and
electrical conductivity.
Ground Penetrating Radar has been used even
since 1970’s as a tool for investigating geological
problems (Annan and Davis, 1976, Olhoeft, 1984,
Davis and Annan, 1989). If early surveys were
oriented in arc haeological applications such as
voiding evidence (Greenwood and Raines, 1991), in
time, this technique is now included in many
environmental studies such as pipes detection, chalk
investigation, geotechnical investigations, landslides
and slope stability, coastal sediments transport
(McCann and Forster, 1990; Conway et al., 1980;
Raines et al., 1999; Stevens et. al., 1995; Peisser et.
all, 2003).

E. Gamma -ray spectometry:

Gamma -ray spectrometry is a very useful tool in
scope of spatial distribution determin ation of some
soil radionuclides such as 40K, 232Th and 238U. The
quantity of soil radionuclides depends mostly on the
parent material of soil, geochemistry, mineralogy,
and soil environmental accumulation. This
properties may be also influenced by spatial
distribution , climatic conditions of soil pedogenesis
processes and relief .
Studies using gamma -ray spectrometry as a soil
investigation method, are commonly used in

agricultural application such as evaluation of soil
properties like texture, pH, total organic carbon and
total nitrogen (H. S. Mahmood et a l, 2013), in
erosion mapping of soils, soil assessment
investigation (L. Herrmann et. al , 2010).

Figure – Radio nuclide behavior during soil formation
(Bor Krai catchment in N -Thailand, L.Herrm ann et al ., 2010)
IV. CONCLUSIONS
Geophysical methods are a very important
investigation tool of soil properties, being used in
almost all soil studies.
Their utility in applications such as
environmental studies and agricult ure studies will
probably make them become mandatory in the
future studies.

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