Improving soil measurements for boundary layer research

The temperature profile in the soil is an important parameter to determine the surface heat exchange. It is measured by a set of 9 temperature needles down to a depth of 50 cm. A new, high accuracy setup has been developed.
In this setup, specially designed Pt needles have been selected which have a horizontal sensitivity of 30 cm. All needles are individually calibrated and KNMI's accurate sensor interface SIAM is used to collect the data. The sensors are installed sideways into the soil using specific techniques to keep soil disturbance to a minimum. The cables coming from the needles are routed horizontally to prevent water and heat transport along the cables. A double configuration is used to prevent disturbing the soil in case of a sensor malfunction. In order to monitor long-term drift, two additional sensors are also installed which are calibrated on a yearly basis.
An error analysis shows that with all the above mentioned measures, the resulting relative accuracy between the sensors is about 5 mK.
In addition to the temperature profile, new self-calibrating heat flux sensors are also being installed