Correcting the Temperature Influence on Soil Capacitance Sensors Using Diurnal Temperature and Water Content Cycles

Abstract

The influence of temperature on the dielectric permittivity of soil is the result of counteracting effect that depends on the soil's composition and mineralogy. In this paper, laboratory experiments showed that for a given water content, the soil dielectric permittivity was linearly related to the temperature, with a slope (α) that varied between samples taken in the same soil. These variations are difficult to predict and therefore, a simple and straightforward algorithm was designed to estimate α based on the diurnal patterns of both the measured dielectric permittivity and the soil temperature. The underlying idea is to assume that soil water content variations can be known with a reasonable accuracy over an appropriate time window within a day. This allows determining the contribution of the soil water content to the dielectric permittivity variations and then, the difference with the observed measurements is attributed to the soil temperature. Implementation of the correction methods in a large number of experiments significantly improved the physical meaning of the temporal evolution of the soil water content as the daily cycles for probes located near the surface or the long-term variations for more deeply installed probes.

Autonomous Sensors for Measuring Continuously the Moisture and Salinity of a Porous Medium

“…Hence, the main mechanism is not related to the polarization of water molecules (or to the thermal dilation of the volume, being negligible: $0.026\%$ °C −1 at $T_0=25$ °C). The phenomenon has been already observed [28,29]. One explanation attributes it to the water bound to particle surface, of which dipoles have a relaxation frequency lower than that of free water dipoles [30], even lower than f of sensors (they operate here at $f=20$ MHz).…”

Hydraulic acclimation in a Mediterranean oak subjected to permanent throughfall exclusion results in increased stem hydraulic capacitance

“…More than 2 years of data are shown here, from sensor installation in December 2016 (DOY 341) until DOY 365 in 2018. Because ε can be affected by temperature (Chanzy, Gaudu, & Marloie, ), two additional probes were installed in dead stems to evaluate the potential effect of the temperature sensitivity of ε ( α = Δ ε /ΔT; °C −1 ) on estimates of ΔStWC. For this, α was estimated on a daily basis as the slope between ε and dead stem temperature (T STEM ; °C) recorded by the probe, and the relationship between α and mean daily ε was evaluated across the surveyed period.…”

Dynamic niche partitioning in root water uptake facilitates efficient water use in more diverse grassland plant communities

“…This extraction of soil water extends over the entire active rooting depth. Additionally, soil water flow occurs both at night as well as during the day (Chanzy, Gaudu, & Marloie, ; Khalil, Sakai, Mizoguchi, & Miyazaki, ; Verhoef, Fernandez‐Galvez, Diaz‐Espejo, Main, & El‐Bishti, ), following water potential gradients in the soil profile. Thus, during dry weather conditions, the time series of soil water content shows a clear day‐night signal.…”