Soil moisture Impedance-method (Hydra Probe II)

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Hydra probe.jpg


Parameter to be measured:

Soil moisture


Frequency Domain Sensor working with the so called impedance-method


  • Stevens: Hydra Probe II


  • easy and fast measurement of punctual soil moisture
  • manual as well as continuously logged measurements possible


  • Each sensor has to be calibrated
  • careful application of probe in stony soils
  • Underestimating of permittivity in media with low permitivity (ε > 40, clay and organic soils)

What to watch out for:

  • Good contact between probe and medium has to be prooved



Other related web sites:

Stevens: Manual & Theory


  • Blonquist, JM; Jones, SB; Robinson, DA. 2005. Standardizing characterization of electromagnetic water content sensors: Part 2. Evaluation of seven sensing systems. VADOSE ZONE JOURNAL 4(4), 1059-1069.
  • Kelleners, TJ; Ferre-Pikal, ES; Schaap MG; Paige, GB. 2009. Calibration of Hydra Impedance Probes using Electric Circuit Theory. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL 73(2), 453-465, DOI: 10.2136/sssaj2008.0151.
  • Kelleners, TJ; Norton, JB. 2012. Determining Water Retention in Seasonally Frozen Soils Using Hydra Impedance Sensors. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL 76(1), 36-50 DOI: 10.2136/sssaj2011.0222.
  • Logsdon, SD; Green, TR; Seyfried, M; Evett, SR; Bonta, J. 2010. Hydra Probe and Twelve Wire Probe Comparisons in Fluids and Soil Cores. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL 74, 5-12, DOI: 10.2136/sssaj2009.0189.
  • Seyfried, MS; Murdock, MD. 2004. Measurement of soil water content with a 50-MHz soil dielectric sensor. SOIL SCIENCE SOCIETY OF AMERICA JOURNAL 68(2), 394-403.
  • Seyfried, MS; Grant, LE. 2007. Temperature Effects on Soil Dielectric Properties Measured at 50 MHz. VADOSE ZONE JOURNAL 6(4), 759-765.
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