Dielectric Loss and Calibration of the Hydra Probe Soil Water Sensor

Abstract

also use soil dielectric properties to determine . These alternative sensors have received relatively little inde-Widespread interest in soil water content (, m 3 m Ϫ3 ) information pendent study; and critical practical issues related to for both management and research has led to the development of a calibration methodology and application have not been variety of soil water content sensors. In most cases, critical issues addressed. related to sensor calibration and accuracy have received little independent study. We investigated the performance of the Hydra Probe soil The Hydra Probe is an example of the alternative water sensor with the following objectives: (i) quantify the intersensors now available. 1 It is currently in widespread use sensor variability, (ii) evaluate the applicability of data from two (e.g., the Soil Climate Analysis Network of the Natural commonly used calibration methods, and (iii) develop and test two Resource Conservation Service) and has proven to be multi-soil calibration equations, one general, "default" calibration robust under a variety of field conditions. Previous reequation and a second calibration that incorporates the effects of soil search demonstrated that Hydra Probe measurements properties. The largest deviation in the real component of the relative are precise and accurate in fluids with known dielectric dielectric permittivity (ε r ) determined with the Hydra Probe using 30 properties and highly correlated with in soils, indicatsensors in ethanol corresponded to a water content deviation of about ing the potential of the instrument for quantitative mea-0.012 m 3 m Ϫ3 , indicating that a single calibration could be generally surement (Seyfried and Murdock, 2004). It was also applied. In layered (wet and dry) media, ε r determined with the Hydra Probe was different from that in uniform media with the same water found that the calibration relationship varied considercontent. In uniform media, was a linear function of ͌ε r . We used ably among soils and that the manufacturer-supplied this functional relationship to describe individual soil calibrations and calibrations were not accurate for some soils. Important the multi-soil calibrations. Individual soil calibrations varied indepenpractical considerations regarding the use of the Hydra dently of clay content but were correlated with dielectric loss. When Probe remain. These include: (i) the degree of variation applied to the 19-soil test data set, the general calibration outperin response among different sensors (i.e., the inter-senformed manufacturer-supplied calibrations. The average difference, sor variability), which determines if sensor specific calievaluated between ε r ϭ 4 and ε r ϭ 36, was 0.019 m 3 m Ϫ3 for the general brations are required, (ii) the optimal experimental equation and 0.013 m 3 m Ϫ3 for the loss-corrected equation.83712;

Operational assimilation of ASCAT surface soil wetness at the Met Office

“…The soil hydrology is based on a finite difference form of the Richards equation and Darcy's law. The van Genuchten (1980) equations are used to describe the relationship of soil hydraulic conductivity and soil suction to the unfrozen volumetric soil moisture. The van Genuchten soil parameters depend on the soil texture (size distribution of the soil particles and the soil organic carbon content).…”

“…USDA SCAN sites use Stevens vitel hydra probes that measure the dielectric constant of the soil to determine soil moisture (Seyfried and Murdock, 2004;Seyfried et al, 2005). According to the user manual, the probes have an accuracy of 0.03 m 3 m −3 .…”

Multi-decadal analysis of root-zone soil moisture applying the exponential filter across CONUS

“…Conversely, the SCAN, SNOTEL, and USCRN networks all used a Stevens Water Hydra Probe Bell et al, 2013). Seyfried et al (2005) described the calibration approach and how the dielectric measurements from the Hydra Probe sensor were converted into volumetric soil moisture measurements.…”

Integrated sensing of soil moisture at the field-scale: Measuring, modeling and sharing for improved agricultural decision support

“…A drawback of neutron soil sensors is that that utilize radioactive isotopes that could potentially be harmful to humans. Time-domain reflectometry sensors use the dielectric permittivity to accurately infer soil moisture, an example of a TDR sensor is the Stevens HydraProbeII [Seyfried et al, 2005,Stevens, 2013. Time-domain reflectometry technology is generally more accurate than capacitance/frequency domain technology [Seyfried et al, 2005].…”

“…Time-domain reflectometry sensors use the dielectric permittivity to accurately infer soil moisture, an example of a TDR sensor is the Stevens HydraProbeII [Seyfried et al, 2005,Stevens, 2013. Time-domain reflectometry technology is generally more accurate than capacitance/frequency domain technology [Seyfried et al, 2005]. The HydraProbeII is that is more expensive and durable then the Decagon line of soil moisture sensors but less expensive than the neutron soil moisture sensors.…”