This study published in American Meteorological Society’s BAMS journal demonstrates the extent of variability in readings one can expect with a soil moisture sensor based on capacitance technology.
To obtain the highest level of accuracy that is required for remote sensing applications, capacitance-based soil sensors often need to be recalibrated. The HydraProbe is an impedance-based sensor that that takes the measurements one step further and rarely needs to be recalibrated. If a custom calibration is necessary, it can be used with any HydraProbe (low inter-sensor variability). The HydraProbe will hold that calibration (custom or factory) for many years (5 years guaranteed) which will save operational costs in long term monitoring networks.
If you are using soil sensors for ground truthing, why not make it easy with a non-capacitance based soil sensor like the HydraProbe?