Electromagnetic Pulse Sounding for Surveying Underground Water
Creators:Caldecott, Richard S.
Irons, D. A. Jr
Moffatt, D. L.
Peters, L. Jr
Puskar, R. J.
Toth, J. F.
Young, J. D.
Contributors:United States. Office of Water Resources Research
Ohio State University. Water Resources Research
MetadataShow full item record
Publisher:Ohio State University. Water Resources Center
Series/Report no.:Project completion report (Ohio State University. Water Resources Center) ; no. 401X
A number of approaches have been explored for measuring the water content of soil electrically. In contrast with traditional measurements, which utilize electric currents at DC or at specific frequencies, our techniques have been based on the transmission and reflection of sharp, regularly repeated pulses. Such pulse measurements can be shown to be equivalent to measuring the electrical properties at all frequencies in a very wide band, and therefore the possibility of extracting the desired information is much greater than with single-frequency measurements. Because the information content of the signal is great, data processing can be used to extract those features which relate most directly to moisture content and reject those which appear to depend more on soil inhomogenieties. For example, it was found that the attenuation in the frequency band of approximately 10 to 20 MHz had a much higher correlation with soil moisture than that in other frequency bands for the actual field conditions under which our measurements were made. This information content increase is obtained by means of sophisticated research equipment. The measurements reported herein were made and processed under real-time computer control. They include the signal scattered from known buried targets, transmission measurements through the ground, and the measurement of reflections in a coaxial test cell, all with pulses containing very wide frequency bands. The results are encouraging in that definite correlations with moisture were found. Unfortunately the one-year time limitation of this effort, much of it spent in instrumentation development, was insufficient to allow testing these correlations quantitatively over extended time periods or in a variety of locations. Thus the techniques must be evaluated at present as promising, but not fully proven. It should be noted that, while the research system to obtain this information is complex, field equipment based on these techniques need not be unduly complicated or expensive. Once the features relating to moisture content under the greatest variety of field conditions are identified, means for extracting this information more simply should be devised. This is proposed as the objective for continuation of this effort.
This project supported in part by the Office of Water Resources Research U. S. Department of the Interior Washington, D. C. under Project B-028-OHIO
Summary -- Introduction -- 1. The Measuring System -- 2. Data Processing -- 3. Underground Moisture Content Monitoring by Measurement of Buried Target Signatures -- 4. Sampled Moisture Conditions -- 5. Underground Propagation Experiment -- 6. Reflection Measurements on Soil Samples in a Vertical Coaxial Test Cell -- 7. Propagation Calculations -- Conclusions -- Recommendations -- References -- Appendix I - Transmission Measurements using a Buried Antenna