EC-5 Soil Moisture Sensor

The EC-5 measures soil moisture by sending an RF pulse into the soil to measure the dielectric constant.  The frequency used is sensitive to soil moisture (but not soil ice) and is relatively insensitive to the soil salinity.  Nevertheless, the manufacturer recommends performing a soil-specific calibration for the local site.  Thus, standard ISFS procedure is to take three gravimetric samples at each EC-5 site for every deployment, that is usually used to generate an offset that later is applied to each reading.  ISFS typically deploys this at about 3cm depth, intended to represent the average soil moisture in the 0-5cm deep layer of soil above the soil heat flux plate at 5cm depth.  To avoid surface effects, the probe is mounted with the printing upside down due to the probe constructiion.  ISFS adds a PIC processor with an A/D to ingest the data for each sensor.