Form Approved
REPORT DOCUMENTATION PAGE
OMB No. 0704-0188
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1. AGENCY USE ONLY (Leave blank)
2. REPORT DATE
3. REPORT TYPE AND DATES COVERED
January 1998
4. TITLE AND SUBTITLE
5. FUNDING NUMBERS
Soil Moisture Determinations Using Capacitance Probe Methodology
6. AUTHORS
Ronald T. Atkins, Timothy Pangburn, Roy E. Bates, and Bruce E. Brockett
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)
8. PERFORMING ORGANIZATION
REPORT NUMBER
U.S. Army Cold Regions Research and Engineering Laboratory
72 Lyme Road
Special Report 98-2
Hanover, New Hampshire 03755-1290
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)
10. SPONSORING/MONITORING
AGENCY REPORT NUMBER
Office of the Chief of Engineers
Washington, DC 20314-1000
11. SUPPLEMENTARY NOTES
For conversion of SI units to non-SI units of measurement, consult ASTM Standard E380-93, Standard Practice for Use of the
International System of Units, published by the American Society for Testing and Materials, 1916 Race St., Philadelphia, Pa.
19103.
12a. DISTRIBUTION/AVAILABILITY STATEMENT
12b. DISTRIBUTION CODE
Approved for public release; distribution is unlimited.
Available from NTIS, Springfield, Virginia 22161
13. ABSTRACT (Maximum 200 words)
Determining soil moisture content by measuring the dielectric constant of the soil is not a new concept. However,
determining the dielectric constant by measuring capacitance directly rather than through the use of time
domain reflectometry (TDR) systems is a relatively new approach to soil moisture measurements. A unique
probe assembly and a readout device that measures voltage drop and phase shift were developed and used for
direct capacitance measurements. The capacitance measurement was calibrated using known capacitors and
resistors. Soil moisture measurements were calibrated by adding known amounts of distilled water to dry soil
enclosed in a known volume. The effect of salinity on the measurement technique was evaluated. Once
calibration had been accomplished, actual soil moisture measurements at three test depths through an entire
winter's freezethaw cycle demonstrated the feasibility of using this capacitance measurement system. The
dielectric constants measured using this fixed-frequency capacitance measurement system fall within the same
general range as the values obtained using TDR equipment with the Topp or Roth general calibration equations,
and they could probably be used directly in these equations after minor corrections. The conclusions drawn from
these tests are that this measurement technique could and should be developed as an easier, more economical,
and more easily automated and calibrated system for soil moisture measurement.
14. SUBJECT TERMS
15. NUMBER OF PAGES
49
Gravimetric sampling
Soil dielectric constants
Moisture content
Soil moisture
16. PRICE CODE
Soil capacitance
Time domain reflectometry
17. SECURITY CLASSIFICATION
18. SECURITY CLASSIFICATION
19. SECURITY CLASSIFICATION
20. LIMITATION OF ABSTRACT
OF REPORT
OF THIS PAGE
OF ABSTRACT
UNCLASSIFIED
UNCLASSIFIED
UNCLASSIFIED
UL
Standard Form 298 (Rev. 2-89)
NSN 7540-01-280-5500
Prescribed by ANSI Std. Z39-18
298-102
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