Laboratory vs. Field Calibration of HydraSCOUT Probes for Soil Water Measurement

Field calibration of DFM capacitance probes for continuous soil moisture monitoring

“…The need for accurate soil moisture estimates at high temporal and spatial resolution is becoming more urgent to support efficient water management, agricultural productivity, drought management and flood forecasting within the context of climate change modelling and adaptation (Pegram et al, 2010;Seneviratne et al, 2010;Ojo et al, 2015b;Tfwala et al, 2019a). Consequently, there has been a dramatic increase in the number of remote-sensing products and hydrological models to estimate soil moisture instantaneously at high temporal and spatial resolution (e.g.…”

“…Multi-depth capacitance sensors have become the most popular devices for real-time, continuous and non-destructive soil moisture profile measurements, due to their lower cost compared to TDR (Bello et al, 2019;Dhakal et al, 2019;Hajdu et al, 2019;Kassaye et al, 2019;Tfwala et al, 2019a). Capacitance sensors measure the apparent dielectric permittivity of the soil, which is much lower than that of water, such that the output is related to the volumetric moisture content in the soil (θ v ), via either the manufacturer's default calibration equation or a user's site-specific calibration equation (Cobos and Chambers, 2010;Gabriel et al, 2010;Archer et al, 2016;Parvin and Degré, 2016).…”

“…A generalized calibration equation, relating the relative sensor output to θ v , which is often supplied by the manufacturer, provides an accuracy of ±3% for typical soils, depending on the specific type of sensor (Cobos and Chambers, 2010). However, irrespective of the stipulated accuracy level claimed by the manufacturers, capacitance probes have been reported to require calibration for different soil types to attain accurate soil moisture measurements, with errors being reduced to ±1% (Fares et al, 2011;Kinzli et al, 2011;Paraskevas et al, 2012;Bogena et al, 2017;Bello et al, 2019;Hajdu et al, 2019;Kassaye et al, 2019;Tfwala et al, 2019a). Some of the reasons for this observation are due to differences in electrical conductivity and soil dielectric properties (Gabriel et al, 2010;Kinzli et al, 2011).…”

“…Some of the reasons for this observation are due to differences in electrical conductivity and soil dielectric properties (Gabriel et al, 2010;Kinzli et al, 2011). Capacitance probes can be calibrated in the laboratory or in the field for specific textural classes, irrespective of site (Gabriel et al, 2010;Zerizghy et al, 2013;Bello et al, 2019;Tfwala et al, 2019a). However, capacitance probes have been reported to have required site-specific calibrations to attain more accurate soil moisture measurements (Fares et al, 2011;Kinzli et al, 2011;Paraskevas et al, 2012;Bogena et al, 2017;Bello et al, 2019;Dhakal et al, 2019;Hajdu et al, 2019;Kassaye et al, 2019;Tfwala et al, 2019a).…”

“…Site-specific calibration equations are generally derived either through laboratory analyses or field techniques, by establishing relationships between the sensor readings and gravimetrically measured θ v at different moisture levels (Kinzli et al, 2011;Archer et al, 2016;Hajdu et al, 2019). Studies have shown that laboratory calibration equations developed using undisturbed soil samples are more accurate than field calibration equations (e.g., Geesing et al, 2004;Gabriel et al, 2010;Kinzli et al, 2011;Bello et al, 2019;Hajdu et al, 2019;Tfwala et al, 2019a). The high accuracy of laboratory calibration equations over field calibration equations is attributed to the wide range of soil moisture contents, ranging from permanent wilting point to saturation, and a relatively large number of replicates of continuous measurements in the laboratory (Gabriel et al, 2010;Varble and Chávez, 2011;Bello et al, 2019;Tfwala et al, 2019a).…”