HR: 1340h
AN: H53G-1509    [Abstracts]
TI: Using an RC Circuit Model to Determine Soil/Water Content
AU: * Buehler, M G
EM: mbuehler@decagon.com
AF: Decagon Devices, Inc., 2365 NE Hopkins Ct., Pullman, WA 99163, United States
AU: Cobos, D R
EM: doug@decagon.com
AF: Decagon Devices, Inc., 2365 NE Hopkins Ct., Pullman, WA 99163, United States
AU: Campbell, C S
EM: colin@decagon.com
AU: Campbell, G S
EM: gaylon@decagon.com
AB: Accurate soil/water content measurements are essential for water conservation. We have developed a soil/water content measurement probe that is simple to deploy, not affected by the salinity, and is corrosion proof leading to extremely long field life. The measurement takes advantage of the high dielectric constant for water (~80) compared to that of soils (3 to 7) to determine the soil/water content. The RC circuit model for the soil/water mixture consists of a bulk conductivity resistor, a double-layer capacitor, and a bulk dielectric capacitor. Since our electrodes are not directly exposed to the soil, the overall RC circuit model includes a blocking capacitor. Measurements of the differential phase angle are acquired across an on-board drive resistor at a single frequency (70 MHz). Measurements are proportional to bulk soil/water dielectric constant for salinities as high as 5 dS/m. The slight temperature dependence of the dielectric constant is compensated for by an on-board temperature sensor. Water content is determined using a soil/water mixing model. Using the RC circuit model, we will show that our choice of measurement frequency is optimal in achieving a salinity-independent measurement of soil/water content.
DE: 1829 Groundwater hydrology
DE: 1847 Modeling
DE: 1866 Soil moisture
DE: 1894 Instruments and techniques: modeling
SC: Hydrology [H]
MN: 2007 Fall Meeting