To address those applications Landviser, LLC has developed and commercialized first model of LandMapper ERM-01 in 2004, which was able to measure electrical resistivity with central-symmetric four-electrode probes of Shlumberger and Wenner configurations to the depth of five meters. Device became popular among agricultural researchers in USA and Europe, and was tested for fast mapping and monitoring of agricultural and horticultural lands (Pozdnyakova et al., 2004; Paillet et al., 2010; Duncan et al., 2008; Carrow and Duncan, 2004).

published in December, 2010 issue of FastTIMES, online peer-reviewed journal of EEGS. To cite this publication use:

Abstract

On-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 sandy soils, such as Alfisols and Spodosols. 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.

The most downloadable PDF publication on Landviser, LLC website is our proceedings paper on 2002 World Congress of Soil Science. So we decided to publish it on our site as our first interactive eBook. It a short synopsis of our research on application of electrical geophysical methods to study soil genesis and provides theoretical background to all applied case studies. To cite this presentation use:

 Abstract

The electrical fields in the surface of soils appear as many different kinds. Methods of self- potential (SP), electrical profiling (EP), vertical electrical sounding (VES), and non-contact electromagnetic profiling (NEP) was used to measure the electrical properties of basic soil types, such as Spodosols, Alfisols, Histosols, Mollisols, and Aridisols (USA Soil Classification) of Russia in situ. The density of mobile electrical changes, reflected in measured electrical properties, was related to many soil physical and chemical properties. Soil chemical properties (humus content, base saturation, cation exchange capacity (CEC), soil mineral composition, and amount of soluble salts) are related to the total amount of charges in soils. Soil physical properties, such as water content and temperature, influence the mobility of electrical charges in soils. The electrical parameters were related with soil properties influencing the density of mobile electrical charges in soils by exponential relationships based on Boltzmann's distribution law of statistical thermodynamics (r=0.657-0.990). Generally, the electrical methods can be used for in situ soil mapping and monitoring when the studied property lone highly influences the distribution of mobile electrical charges in the soil. The electrical properties were used to improve soil characterization for soil morphology and genesis studies; to develop accurate soil maps for precise agriculture practices; and to evaluate soil pollution, disturbance, and physical properties for engineering, forensic, and environmental applications.

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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:

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:

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Guest post by Dr. Leonid Anisimov, Principal Scientist of Lukoil-Engineering, Volgograd, Russia. VolgogradNIPImorneft – scientific center of the LUKOIL Oil Company for the South Volga, Caspian Region and Middle East.

Shalow gas accumulations in shale deposits are unconventional energy resources. However those are hazardous objects for drilling especially in the offshore areas.
Seismic is a principal instrument to detect shallow gas pockets but electromagnetic methods may have advantage. The presentation below shows principal geography and techniques for detection and development of shale gas fields. A pilot project of Landviser LLC in using VES for monitoring accumulation and release of methan in peat bogs of Eastern Siberia is attached.

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Example of electrodes arrangement and measurement sequence that can be used for a 2-D electrical imaging survey is shown on the left. Many different multi-electrode systems have been developed over the past 15 years using different arrangements of the cables and measurement strategies (Loke, 2011). This program is designed to invert large data sets (with about 200 to 100000 data points) collected with a system with a large number of electrodes (about 25 to 16000 electrodes). The survey is usually carried out with a system where the electrodes are arranged along a line with a constant spacing between adjacent electrodes. However, the program can also handle data sets with a non-uniform electrode spacing. RES2DINV program can be used for surveys using the Wenner, pole-pole, dipole-dipole, pole-dipole, Wenner-Schlumberger, gradient and equatorial dipole-dipole (rectangular) arrays. In addition to these common arrays, the program even supports non-conventional arrays with an almost unlimited number of possible electrode configurations (Loke et al. 2010). You can process pseudo sections with up to 16000 electrode positions and 70000 data points at a single time on a computer with 4 gigabytes (GB) of RAM. Besides normal surveys carried out with the electrodes on the ground surface, the program also supports aquatic and cross-borehole surveys.

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The valley landscapes of humid areas are dominated with peat soils of various origins, which become the most productive soils after the proper drainage and cultivation. The high fertility and proximity to water make peat soils the most desirable for vegetable production. However, these soils are also subject to quick degradation during agricultural usage. Excess drainage increases the unproductive decomposition and mineralization of peat and can cause spontaneous ignition of peat soils, whereas little or no drainage can be non-sufficient for normal agricultural practices. Therefore, drainage design and the following agriculture practice on peat soils should be based on careful studies of the peat soil genesis and hydrology of the areas.

 Method VES is suitable for detection the resistivity in different soil and geological strata without digging or boring. Usually, peat shows not much difference in electrical properties along the profile. Water content of cultivated peat soils is close to the field capacity during the whole growing season.

The 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.

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%.