Constant energy calibration for permittivity based moisture probes

Soil moisture or soil water content (SWC) is an important variable and its determination with an acceptable accuracy is an essential need for a variety of hydrological disciplines. Among the alternatives, permittivity based probes are gaining popularity and becoming established techniques. However, probes are affected by local soil conditions, requiring soil-specific calibrations for accurate and reliable measurements. Measurement errors associated with these probes can be classified in three groups as primary, secondary and tertiary. Primary errors are mostly associated with the underlying operating principles of a probe. Soil density variation is inherently the major source of secondary error as it can create a measurement error as much as 0.030 m3 m−3. The error associated with the secondary variables can be reduced by up to 0.015 m3 m−3 by targeting the half range of the density variations. Currently available techniques do not explicitly quantify/minimize the secondary errors. Tertiary errors arise mostly from user dependent factors associated with probe-soil contact discontinuities and unexpected small scale environmental variations in the vicinity of the measurement point.