Ground Conductivity Meter Research Articles

MOBILIZED SURVEYING OF SOIL CONDUCTIVITY USING ELECTROMAGNETIC INDUCTION

Established and emerging geophysical technologies offer many promising applications for precise nearsurfacesurveying. Scientists are investigating these noninvasive surveying techniques to enhance soil mapping and research. Anoninvasive soil surveying system was developed to rapidly map soil characteristics. This system employs an allterrainutility vehicle towing a nonmetallic carriage that cradles a commercially available ground conductivity meter. Autonomousdata streams of timestamped soil conductivity data and global positioning system (GPS) data are immediately downloadedto a computer after a survey. Both data sets are automatically merged using the time stamp data as an index. Usinggeographical information software (GIS), conductivity maps of increased data density are produced onsite.<br><br>The mobile surveying system increased total conductivity sampling rate by a factor of >100, and increased data densityby a factor of >10 over a conventional manual survey method when operating over a 1ha open test site. For open fields thatcan be easily traversed with a utility vehicle, the mobile surveying system was found to greatly enhance data quality byincreasing data density, and to dramatically increase both data acquisition efficiency and data postprocessing speeds.

Noninvasive Soil Water Content Measurement Using Electromagnetic Induction

The feasibility of soil water content measurement using electromagnetic induction was investigated in an arid region of southern New Mexico. Soil water measurements were taken monthly with a neutron probe at 65 equally spaced stations along a 1950‐m transect. At the same time, noninvasive electrical conductivity measurements of the soil were taken with a Geonics EM‐31 ground conductivity meter. Using 16 months of measurements, we found a linear relationship exists between bulk soil electrical conductivity and total soil water content in the top 1.5 m of the profile. A simple linear regression model was developed to describe the relationship between soil water content and bulk soil electrical conductivity. The spatial and temporal accuracy of the regression model is addressed as well as the total number of neutron access tubes needed to accurately calibrate the model. By comparison with the neutron scattering method the electromagnetic induction method is quite accurate for the prediction of water content changes over time. The speed and ease of use combined with the accuracy of the measurements make the ground conductivity meter a valuable tool for rapid, noninvasive soil water measurements.

GPS System Integration and Field Approaches in Precision Farming

Two phases of a precision farming project are described. Phase I consists of the collection of data from four test fields across Alberta using differential GPS (DGPS I combined with crop yield monitors and electromagnetic f EM) ground conductivity meters for measuring salinity. A geographic information system (GIS) is used to analyze and combine various layers of information obtained from each field in order to analyze yield variation. Positions better than 50 cm horizontally and 1 m vertically are obtained in DGPS mode using a robust carrier-phase smoothing of the code approach. The accuracy of the DGPS positions is verified independently through a crossover point analysis and a comparison with an ambiguity resolution on the fly t OTF) solution. DGPS positions are used to generate maps, which indicate that fields are not homogeneous in crop yield when they have been treated wlthout consideration for variability of soil, salinity, topography, or field history. Phase II, which consists of the application of variable-rate fertilizer based on the information gathered in Phase I, is summarized.

Sodium‐Affected Soil Identification in South‐Central Illinois by Electromagnetic Induction

AbstractThe irregular shape, small size, and spotty occurrence of sodium‐affected soils (NaAS) in moderately thick to thin loess over Illinoian till have continued to slow mapping in south‐central Illinois. Use of a Geonics EM‐38 ground conductivity meter to recognize soils with natric horizons in Tennessee suggested that this device would be useful in Illinois. We selected eight areas of NaAS in five counties of south‐central Illinois to find if the EM‐38 would be useful for predicting exchangeable sodium percentage (ESP). Approximately 225 observation points, spaced at 10‐m intervals, were established in each area and 107 sample cores were collected for laboratory analyses. Weighted averages of the ESP, electrical conductivity of the saturation extract from a saturated soil paste (ECe), and field pH data for 0 to 75‐ and 75 to 150‐cm depths were compared with the horizontal (EMh) and vertical (EMv) responses and the mean ESP data increases with depth, i.e., 7.0 at 35 cm, 9.7 at 75 cm, and 12.5 at 135 cm. The EMh readings correlate almost as well with ESP (r = 0.73) as with ECe (r = 0.76) for the 0‐ to 75‐cm depths. The EMv readings correlate slightly better with ESP (r = 0.76) than with ECe (r = 0.68) for the 75‐ to 150‐cm depth. These results show that EM readings may by used to predict ESP. The correlations of the depth‐weighted average ESP at the maximum depth for meeting natric horizon criteria in these soils (75 cm), and the EMv readings show that the EM‐38 provides a rapid and accurate method to describe the composition of the map units of NaAS on moderately thick to thin loess over Illinoian till in south‐central Illinois.

Advances in electromagnetic methods for groundwater studies

In the past decade, both inductive electromagnetic survey instrumentation and associated interpretive techniques have become refined to the point that electromagnetic techniques are widely used for geological mapping as well for the direct detection of conductive ore bodies. Electromagnetic survey techniques have been particularly successful in exploration for potable groundwater, for measuring salinity levels in aquifers and monitoring coastal saline intrusion, and for mapping soil salinity in connection with crop growth. Regardless of the techniques employed, it is the terrain conductivity that is measured, and it is a particular advantage of electromagnetic techniques that small variations in the bulk conductivity of the terrain can often be detected. A further advantage is that most electromagnetic techniques allow measurements to be made rapidly, and survey costs are generally less than those associated with conventional DC resistivity surveys or, conversely, larger areas can be surveyed in greater detaul for comparable cost. A disadvantage of electromagnetic instrumentation is that although the shallower units cost about the same as resistivity equipment, the deeper penetration systems are relatively expensive. In general, electromagnetic systems are most effective in looking for the better conductors and are ineffective in searching for resistive material. In all cases some knowledge of electromagnetic theory is desirable for a successful interpretation. In this paper we present several case history selected from the literature in which a variety of electromagnetic systems (horizontal loop EM, ground conductivity meters and VLF) are used either alone or in conjunction with conventional resistivity to explore for groundwater.