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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

Cenozoic Shale Formations as a New Frontier Area - detecting shallow natural gas fields

methane emission on peat bogGuest 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.

Locations

Houston 29° 45' 36.6948" N, 95° 22' 9.804" W
56° 52' 40.7964" N, 60° 55' 48.6336" E
43° 46' 4.5048" N, 11° 15' 8.5644" E

Quick Estimation of Salinity in Field Soils and Irrigation Water with LandMapper ERM-02

ec mapping with Landmapper on dead rice field after hurracaine IkeSoil salinity is routinely evaluated in the labs from electrical conductivity of liquid soil saturation extract (ECe). The resulted total salinity is reported either directly in conductivity units (dS/m) or converted to TDS (total dissolved solids) concentration in ppm (parts per million) using formula: 1 dS/m = 1 mS/cm = 1 mmho/cm = 640 ppm = 640 mg/L= 0.64 g/L=0.064%

But now EC of soil and waters can be measured directly in the field using highly accurate method of four-electrode probe and Landmapper ERM-02 measuring device. Best of all, probes can be build to sense different soil layers down to 30 ft! Probes are simple and inexpensive to make from common materials available at any hardware store.

For irrigation water and soil solutions: To measure ECw just put 4-electrode probe of Landmapper used for mapping into a ditch, canal, or other water source. Make sure that all 4-electrodes are in contact with water. Take a reading in EC (conductivity) mode. Display will read (example):  
K0*C= 150m  - which indicates milli Siemens (mS/m)
To convert to dS/m, divide display number by 100, i.e. 150 mS/m=1.5 dS/m.

Vertical Electrical Sounding to detect peat deposit thickness and drying depth

VES to detect peat deposit depthThe 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.

Soil Science

Applications of electrical geophysical methods in classic Soil Science (Pedology, Soil Genesis and Classification) - browse the links and maps on this page to find out more...

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

Vertical Electrical Sounding to Detect Soil Salinity in Arid Areas

total soil salinity vs resistivity by VESWater and salt content distributions within the soil profile are the main properties causing considerable variations in electrical resistivity or conductivity.  Since the evaporation in the arid areas (Astrakhan, Russia) is about five times higher than the precipitation, the water content and salt distributions are determined mainly by the saline groundwater.

The differentiation of salinity in the unsaturated zone of the soil profiles was revealed by small fluctuations of electrical resistivity in upper part of the VES profiles. We thoroughly interpreted the VES results to estimate the layers with different electrical conductivities (EC) for 12 soil profiles. The total salt content was measured in soil samples collected from the layers of the profiles as shown in Table (columns 1 and 2) for one example profile. 

Evaluation of stone contents in soils with electrical geophysical methods to aid orchard planning

VES of stony soils in Crimea

Establishments of orchards and vineyards are long-term and money-intensive, but highly pay-off projects. This study allowed developing procedure for incorporating geophysical survey data into recommendations of usage skeletal soils under orchards. Geophysical methods of electrical resistivity, such as VES and four-electrode profiling provided the information about spatial distributions of stones in skeletal soils.  The resistivity of rocks or stones is much higher (about 104-1012 ohm m) than the resistivity of soil horizons with any texture. Therefore, high resistivity will indicate the presence of stones in soil profiles.

Study was conducted on skeletal soils (Paleoxerolls and Lithic Xerorthents) formed on carbonate-cemented marine deposit, limestone, or pebbles of alluvial origin in western part of Crimea Peninsula, Ukraine. The stone content varied from 2 to 90% of fragments coarse than 2 mm by volume and stony layers occurred in soil profiles at the depth as shallow as 12 cm.

Location

Saky
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