Improving Soil Moisture Monitoring Networks By Implementing Lab and Field Sensor Calibration Protocols.

Proper calibration of soil moisture sensors is a necessary step towards generating accurate soil moisture observations and to ensure the overall reliability of in situ networks. In this study we developed laboratory and field protocols to calibrate the CS655 reflectance soil moisture sensor. The CS655 sensor has been deployed across the stations of two small-scale (< 1 Km²) and a state level network, the Kansas Mesonet. Laboratory set up consisted of packing different soils to a known volumetric water content. Dielectric permittivity, bulk electrical conductivity, and soil temperature were recorded from the CS655 sensors to create custom calibration equations to estimate volumetric water content. Custom calibration equations were compared to factory default volumetric water content estimates. Custom calibration equations involving the square root of the dielectric permittivity and the bulk electrical conductivity resulted in estimations of volumetric water content with root mean square error (RMSE) of 0.0081 m³ m^-3, a value four times lower than the RMSE obtained using the default factory equation.