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Frequently asked questions (FAQ) on electrical geophysical equipment and software

How to convert conductivity to resistivity?

Are there any difference between LandMapper ERM-01 and other equipment available on the market?

How your equipment calculates electrical resistivity?

How to calculate geometrical coefficient K?

Does electrical resistivity correlate with any soil properties?

Can your equipment measure electrical resistivity/conductivity in soil and water samples?

How to determine the depth of the measurements?

More help...

How to convert conductivity to resistivity?

Electrical resistivity (ER) is reciprocal to conductivity (EC) and results can be easily recalculated using formula EC=1/ER or vice versa ER=1/EC. Electrical resistivity is more convenient to use on non-saline soils, where conductivity can be mSm/m, while resitivity measures in 102-103 Ohm m range. 1000 Ohm m equals 1 mSm/m. You can find more conversions to ppm, TDS, grains of salt in this flyer.

LandMapper - fast, portable, versatile, affordable EC ER SP meterAre there any difference between LandMapper ERM-01 and other equipment available on the market?

LandMapper ERM-01 is based on pulsating DC current, which principle fully accounts for spontaneous polarization arising at the electrode contacts with soil. This allows to measure electrical resistivity fast (4 sec at one location) and with great accuracy. Geonics EM-series uses electromagnetic induction principle and AC current to measure electrical conductivity without any contact with the ground. Although such measurements are very fast they are subjected to electrical interference from nearby metals and sources of electricity. Besides, not a single modification of EM method can evaluate soil layer shallower than 0.5 m. Soil EC mapping systems supplied by Veris Technologies, Inc. imply the same four-electrode principle as LandMapper ERM-01, but their equipment is tailored to precision farming market and can be used only with motorized vehicle on arable fields. LandMapper ERM-01 is more compact and versatile and can be used anywhere where a person can walk, i.e. in forestry, wetland and road assessments, construction sites, golf courses, etc. Ground penetrating radar (GPR) evaluates profile differentiation of soil electrical conductivity in shallow subsurface, but its application is limited on soils with high conductivity, such as salty and clay soils (Liner and Liner, 1997). LandMappers, both ERM-01 and ERM-02 models, measure EC and ER in widest range occuring from solid rocks and ultra-pure water to saline soils and ocean waters! Our LandMapper ERM-02 device also can measure natural electrical potential (self-potential) in soils, plants and other biological objects. LandMapper was recently featured in Encyclopedia of Solid Earth Geophysics (2011).

How the equipment calculates electrical resistivity?

LandMapper applies a pulsating current (I) through electrodes A and B and measures arising potential (ΔU) on electrodes MN in well-known four-electrode principle described by van der Pauw and Wenner. Electrical resistivity calculated from the Ohm’s law as

where K is the geometrical coefficient of the array. The equipment calculates ER automatically if the user enters an appropriate coefficient into the device memory.

How to calculate geometrical coefficient K?

If you using the equipment with the supplied array or laboratory cuvette, the right coefficient are already calculated. However, if you want to use your own array, the geometrical coefficient can be calculated from the distances between electrodes as follows.

For any array:

For center-symmetric array:

Does electrical resistivity correlate with any soil properties?

Electrical resistivity is correlated with a number of soil properties, which influence density of mobile electrical charges. For saline soils these properties are the total salinity and sodium adsorption ratio (SAR). For non-saline soils the relationships have been developed with soil texture, stone content, cation exchange capacity, humus content, Ca+Mg, etc. It is important to understand that soil electrical resistivity or conductivity are complex characteristics of soil and should be used together with other conventional methods of soil analysis. The usual path is to delineate the soil survey area into regions with different resistivity and than sample those areas to determine what properties are causing these differences. In some cases only one or two soil properties primarily influence electrical resistivity, and field electrical methods can be used to evaluate those properties in-situ. See "Soil Electrical Properties" - Ph.D. Thesis by L. Pozdnyakova or papers attached to this page.

Can your equipment measure electrical resistivity/conductivity in soil and water samples?four-electrode lab cell

Yes. The optional 4-electrode cell can be purchased from us or obtained from AGI, Inc., or other companies providing standard geophysical equipment, or can be constructed by user. Using the cell you can measure electrical resistivity or conductivity in soil samples, soil pastes and suspensions, or water, juices, etc.

How to determine the depth of the measurements?

 For the Wenner array, when all the electrodes are equally spaced (AM=MN=NB=a) the depth of the measurements is approximately equal to the distance between electrodes (a), for Schlumberger center-symmetric arrays (MN<<AB) the depth of the measuring is about ¼ to 1/6 of the AB distance (Barker, 1989). The depth of the measuring depends on electrical resistivity of the soil as well as from the distances among electrodes. Thus, the exact depth can be obtained through the computer interpretation of Vertical Electrical Sounding. The FREE programs for interpretation of the 1D sounding is supplied with the equipment. For full 2D and 3D resistivity interpretation we recommend RES2DINV and RES3DINV software by GeoTOMO Software, very functional DEMO of each is available on this website.

Need more help?

  • Post your question as a comment below.
  • Call Landviser, LLC at 609-412-0555 or send us a email.
  • Browse our public Soil Electrical Geophysics Library
  • Register to receive our newsletters and featured discussions and get access to peer-review paper reprints.

Thank you for this article.

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This is nice post which I was awaiting for such an article and I have gained some useful information from this site.Thanks for sharing this information. Waiting for this type of informative article. Thanks and regards

What is a warranty on

What is a warranty on LandMapper?

Instruments supplied by

Instruments supplied by Landviser are guaranteed for one year against defects in manufacture or materials used. The guarantee does not cover damage through misuse, inexpert servicing, or other circumstances beyond our control. For the US this means that no charges are made for labor, materials, or return shipment for guarantee repairs.
For other countries, the guarantee covers free exchange of faulty parts during the guarantee period. Alternatively, if the equipment is returned to us for guarantee repair, we make no charge for labor or materials but we do charge for shipping and handling and US customs clearance. We strongly prefer to have such repairs discussed with us first, and if we agree that the equipment does need to be returned, we may at our discretion waive these charges.

Larisa Golovko (Pozdnyakova), Ph.D. - President of Landviser, LLC

Can landmapper measure

Can landmapper measure resistivity of solid rocks?

Yes, to measure solid rock

Yes, to measure solid rock samples EC with LandMapper you can use medical patch electrodes, like the ones used in ECG studies and stick them to the rock sample. For relatively big rock, stick electrodes close together so you electrical field (semi-spherical) will not extend outside of the rock sample, and you can calculate K geometrical coefficient in the same fashion as for soil surface measurements. See pic here

Larisa Golovko (Pozdnyakova), Ph.D. - President of Landviser, LLC