ISFS's soil temperature probe is designed to measure temperature at 4 equally-spaced depths in the soil in the first 5cm (nominally above the soil heat flux plate), to calculate the heat storage in the top layer of soil.  The sensors are commercial PRTs encased in a closed stainless steel tube from Omega Engineering.  These sensors are sealed into a 3-D prrinted "handle" to maintain the desired spacing.  Each thermistor is calibrated in a silicon oil bath in EOL's callibration laboratory to better than 0.01 degC.  The data are digitized by a PIC-based microprocessor that applies these calibrations and reports real temperatures.