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Instrumentation, Electrical Resistivity (Solid Earth Geophysics Encyclopedia)

Our unique LandMapper device was featured in 2nd edition of Solid Earth Geophysics Encyclopedia as the best small scale portable and accurate electrical resistivity/conductivity meter. To cite this publication use:

Loke, M.H., J.E. Chambers, and O. Kuras. “Instrumentation, electrical resistivity.” In Solid Earth Geophysics Encyclopedia (2nd Edition), Electrical & Electromagnetic, Gupta, Harsh (ed), 599–604. 2nd ed. Berlin: Springer, 2011. http://www.landviser.net/webfm_send/76
 

The PDF of the article is attached to this webpage. Continue reading excert from the Encyclopedia....

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Instrumentation, Electrical Resistivity

  • Electrical survey. Mapping subsurface resistivity by injecting an electrical current into the ground.
  • Resistivity meter. An instrument used to carry out resistiv­ity surveys that usually has a current transmitter and volt­age-measuring circuitry.
  • Electrode. A conductor planted into the ground through which current is passed, or which is used to measure the voltage caused by the current.
  • Apparent resistivity. The apparent resistivity is the resistiv­ity of an equivalent homogeneous earth model that will give the same potential value as the true earth model for the same current and electrodes arrangement.
  • Multi-core cable. A cable with a number of independent wires.

Introduction

The resistivity survey method is more than 100 years old and is one of the most commonly used geophysical explo­ration methods (Reynolds, 1997). It has been used to image targets from the millimeter scale to structures with dimensions of kilometers (Linderholm et al., 2008; Storz et al., 2000). It is widely used in environmental and engi­neering (Dahlin, 2001; Chambers et al., 2006) and mineral exploration (White et al., 2001; Legault et al., 2008) sur­veys. There have been many recent advances in instru­mentation and data interpretation resulting in more efficient surveys and accurate earth models. In its most basic form, the resistivity meter injects a current into the ground through two metal stakes (electrodes), and mea­sures the resulting voltage difference on the ground sur­face between two other points (Figure 1). The current (I) and voltage (V) values are normally combined into a single quantity, the apparent resistivity, which is given by the following relationship:

Locations

Berlin 52° 31' 9.0156" N, 13° 24' 21.9276" E
8° 0' 14.8032" S, 108° 32' 41.7192" E

LandMapper ERM-02 - versatile and affordable

Landmapper - field EC meter with lab accuracy

Don’t break your back collecting soil samples. Reduce amount of samples sent for laboratory analysis and save money. And still make detail soil map of your fields, which will be more accurate than conventional soil surveys. Impossible? Not at all with LandMapper ERM-02.
This device measures three important electrical properties of soil: electrical resistivity (ER), conductivity (EC), and potential (EP). Utilizing the most accurate four-electrode principle LandMapper measures ER or EC and helps delineate areas with contrasting soil properties within the fields quickly, non-destructively and cost-efficiently.

In a typical setting, a four-electrode probe is placed on the soil surface and an electrical resistivity or conductivity value is read from the digital display. Using the device prior to soil sampling you can significantly reduce the amount of samples required and precisely design a sampling plan based on the site spatial variability.
Bulk soil EC was correlated with salinity, texture, stone content, bulk density, total available nutrients, water holding capacity, and filtration rates. Guided by detailed soil EC map obtained with LandMapper, only minimal amount of soil samples is needed to invert EC map into correlated soil properties. Also, LandMapper can be used to measure EC in soil pastes, suspensions and solutions and quickly estimate total dissolved salts (TDS) in solid and liquid samples.

Locations

Beltsville 39° 2' 5.3952" N, 76° 54' 26.9064" W
34° 57' 16.8984" N, 91° 38' 52.6164" W
56° 17' 1.7628" N, 36° 59' 27.4812" E

Electrical geophysical methods to outline ground water rising in urban areas

Hydrological conditions in Delta Volga, RussiaThe groundwater table rises steadily in the delta Volga, where Astrakhan’ city is located because of irrigation and rising of the Caspian Sea level. The highly saline groundwater enhances secondary salinity in the area. The groundwater caused visible destruction of more than 20% of the buildings in Astrakhan’ city. Natural hazardous groundwater condition in delta Volga was further aggravated in the urban areas by the uncontrolled leakage from the canals and plumbing pipes.

The methods of vertical electrical sounding (VES) and non-contact electromagnetic profiling (NEP) were tested in 1995 for detail outlining of the groundwater table within the representative part of Astrakhan’ city. The study area was located in the center of Astrakhan’ with a large change of elevation, which induced a high variation of groundwater table within the area.map of geophysical survey in Astrakhan City

Profiles of alluvial soils in delta Volga consist of thin layers of silt, clay, and sand. However, only water and salt content distributions within the soil profile cause considerable differentiation of the electrical resistivity in these soils. The soil profile can be generally divided into the top unsaturated layer with high resistivity and the bottom layer saturated by saline groundwater with low resistivity. Considering high distinction in electrical resistivity between unsaturated and saturated zones, the VES method was applied for detection of groundwater table. With the 1-D computer interpretation of the VES data the transition between top layer with high resistivity and bottom layer with low resistivity (i.e. groundwater table) was determined accurately. Compared with the groundwater tables measured in wells, the relative errors of the VES estimation were from 3 to 13%.

1D Vertical Electrical Sounding (VES) with LandMapper Procedure

standard big manual VES cable set by LandviserThe technique and procedure described here can be performed with LandMapper ERM-01 or ERM-02 (set in resistivity mode). The electrode spacings provided in this example are identical to Landviser's supplied "big manual VES" cable set made to measure 16 layers of topsoil down to approximately 9 m. The worksheet for pre-set electrode spacings in such cable re-calculating measured resistivities to 1D VES profile can be downloaded as Manual 1D VES workbook (MS Excel format).

Other electrode spacings are possible for custom-made cable arrays to reach deeper profiles. For example, we developed and tested with LandMapper a 60m-long cable, measuring down to ~ 20 m for one custom hydrology project

This manual VES technique is most convenient to use with three people. Follow step-by-step instructions below. If you need further help, do not hesitate to contact Landviser, LLC @ +1-609-412-0555 or info@landviser.com. Register on our site and download 7 related publications and software!

Locations

San Antonio 29° 25' 26.8392" N, 98° 29' 37.0608" W
Dmitrov 56° 20' 39.0192" N, 37° 31' 2.5716" E

Electrical resistivity in precision cranberry farming

Low ER indicates low cranberry yieldOne of the most important issues in precision agriculture is to develop site specific principles of crop management based on variability of soil and hydrological properties. Accessing spatial variability of soil properties often require high-density and repetitious sampling, which is costly, time-consuming, and labor-intensive. One of the challenges facing the adoption of precision agriculture technology is the identification of productivity-related variability of soil properties accurately and cost-effectively.

The application of the geophysical methods of electrical resistivity makes it possible to define areas of electrically contrasting soils, which have distinct properties and, therefore, should be used in agriculture in different ways. Electrical resistivity is a composite characteristic of soils, which generally related to soil texture, stone, salt, and humus contents, and arrangement of the genetic soil horizons. This is the complex of the factors, which directly influence yield of the most of the crops. The advantage of measuring electrical resistivity is that it can be measured directly in the field without actual taking of soil samples and analyzing them in the laboratory. Thus, implication of the electrical resistivity techniques of soil characterization can tremendously decreases time and labor, required to delineate management zones within the fields.

Locations

Chatsworth, NJ 39° 49' 3" N, 74° 32' 7.0008" W
Puerto Varas 41° 19' 58.6704" S, 72° 58' 55.8408" W

Applications of LandMapper handheld for near-surface soil surveys and beyond

LandMapper - fast, portable, versatile, affordableOn-the-go sensors, designed to measure soil electrical resistivity (ER) or electrical conductivity (EC) are vital for faster non-destructive soil mapping in precision agriculture, civil and environmental engineering, archaeology and other near-surface applications. Compared with electromagnetic methods and ground penetrating radar, methods of EC/ER measured with direct current and four-electrode probe have fewer limitations and were successfully applied on clayish and saline soils as well as on highly resistive stony and sandy soils. However, commercially available contact devices, which utilize a four-electrode principle, are bulky, very expensive, and can be used only on fallow fields. Multi-electrode ER-imaging systems applied in deep geophysical explorations are heavy, cumbersome and their use is usually cost-prohibited in many near-surface applications, such as forestry, archaeology, environmental site assessment and cleanup, and in agricultural surveys on farms growing perennial horticultural crops, vegetables, or turf-grass. In such applications there is a need for accurate, portable, low-cost device to quickly check resistivity of the ground on-a-spot, especially on the sites non-accessible with heavy machinery.

Four-electrode principle of EC/ER measurements

Our equipment utilizes well-known four-electrode principle to measure electrical resistivity or conductivity (Fig).

Locations

Jonesboro, AR 35° 50' 32.2692" N, 90° 42' 15.4044" W
Krasnoyarsk 56° 0' 38.8404" N, 92° 51' 9.99" E

Vertical Electrical Sounding and Self-Potential Methods to Survey for Placement of Potable Water Wells

Science of Geophysics vs Art of DowsingWater is a precious commodity  in most urban and rural areas. Luck of local  potable  water sources threatens not only thriving but a mere survival of rural communities all over the world.  Establishing potable water wells requires a lot of fundings and resources and often cost prohibitive for local governments in South America and Africa.

Searching for shallow groundwater require knowledge of subsurface layers and locating intensity and directions of water fluxes, which can be accomplished with geophysical methods of vertical electrical sounding (VES) and self-potential (SP).  A method of VES can distinguish differences in electrical resistivity or conductivity at the multiple (10+) layers in soil profiles. These differences reveal the changes in soil texture and structure  between water-bearing and waterproof  layers,  which form a framework for  the subsurface water fluxes. 

The directions and intensities of the fluxes  can then be evaluated with the self-potential method. However, conventional equipment for VES and SP is very expensive, bulky and complicated to operate. We tested a simple low-cost handheld device, LandMapper ERM-02, to evaluate layers in the ground with VES method and results were well  correlated with drilled profiles in Central TX.  Information is provided for the VES array assembly, field measuring procedure and interpretation of sounding results. Previously, device was used in Astrakhan area, Russia for estimation of the groundwater table and salinity layers in the soil profiles. The method of self-potential was used to estimate subsurface water flux directions and intensities through the measured variation in electrical potential on the soil surface and direct potable wells placement in Kiev, Urkaine and Dmitrov, Russia.

Cite this presentation:SAGEEP 25 - 2012 - Tucson, AZ
 
Golovko, Larisa, Anatoly Pozdnyakov, and Terry Waller. “A Vertical Electrical Sounding and Self-Potential Methods to Survey for Placement of Potable Water Wells.” In Making Waves: Geophysical Innovations for a Thirsty World. Tucson  AZ: Environmental and Engineering Geophysical Society, 2012. http://www.landviser.net/webfm_send/89

Locations

Water For All International San Angelo, TX 31° 27' 49.5792" N, 100° 26' 13.3368" W
SAGEEP 2012 Tucson, AZ 32° 13' 18.2748" N, 110° 55' 35.3244" W

RES3DINV - 3D inversion geophysical software for resistivity and induced polarization data

RES3DINV software -Create 3D models of subsurface resistivity or IP!
For Windows XP/Vista/7  (available for 32- and 64-bit PCs.)

3D surveys for pole-pole, pole-dipole, dipole-dipole, rectangular, trapezoid, Wenner, Wenner-Schlumberger,and non-conventional arrays.

Now available as a combined package together with RES2DINV, the 2D Resistivity & IP inversion program.
Supports exact and approximate least-squares optimisation methods
Supports smooth and sharp constrasts inversions
Supports up to 5041 electrodes and 67500 data points on computers with 1GB RAM
Supports trapezoidal survey grids
Supports parallel calculations on Pentium 4 (and compatible) based computers
Multi-core support with RES3DINVx32, 128GB memory support with RES3DINVx64

ELECTRICAL POTENTIAL (Self-Potential) MEASUREMENTS with LandMapper ERM-02

Self-potential map to detect directions of water fluxes, KievThe self-potential (SP) method was used by Fox as early as 1830 on sulphide veins in a Cornish mine, but the systematic use of the SP and electrical resistivity methods in conventional geophysics dates from about 1920 (Parasnis, 1997). The SP method is based on measuring the natural potential differences, which generally exist between any two points on the ground. These potentials are associated with electrical currents in the soil. Large potentials are generally observed over sulphide and graphite ore bodies, graphitic shale, magnetite, galena, and other electronically highly conducting minerals (usually negative). However, SP anomalies are greatly affected by local geological and topographical conditions. These effects are considered in exploration geophysics as “noise”. The electrical potential anomalies over the highly conducting rock are usually overcome these environmental “noise”, thus, the natural electrical potentials existing in soils are usually not considered in conventional geophysics.

LandMapper ERM-02, equipped with proper non-polarizing electrodes, can be used to measure such “noise” electrical potentials created in soils due to soil-forming process and water/ion movements. The electrical potentials in soils, clays, marls, and other water-saturated and unsaturated sediments can be explained by such phenomena as ionic layers, electro-filtration, pH differences, and electro-osmosis.

Another possible environmental and engineering application of self-potential method is to study subsurface water movement. Measurements of electro-filtration potentials or streaming potentials have been used in USSR to detect water leakage spots on the submerged slopes of earth dams (Semenov, 1980). The application of self-potential method to outline water fluxes in shallow subsurface of urban soils is described in (Pozdnyakova et al., 2001). The detail description of self-potential method procedure is provided in LandMapper manual.

Another important application of LandMapper ERM-02 is measuring electrical potentials between soils and plants. Electrical balance between soil and plants is important for plant health and electrical potential gradient governs water and nutrient uptake by plants. Monitoring of electrical potentials in plants and soils is a cutting-edge research topic in the leading scientific centers around the world.

Locations

Zamboanga 7° 1' 27.3612" N, 122° 11' 20.0544" E
Kiev-Pechersk Lavra Kiev 50° 24' 59.1768" N, 30° 33' 55.836" E
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