A New Heat Pulse Sensor for Measuring Soil Profile Evaporation.

Evaporation of water from near-surface soil is a key component of hydrological processes, yet few technologies are available for measuring soil evaporation in situ. Recently the heat-pulse probe has been proved to be a promising tool for continuously monitoring water evaporation from soil. Due to its limited measuring volume, however, several heat-pulse sensors are installed at different depths to complete the evaporation measurement at a give site. This brings about the challenge to install the individual sensors accurately at specific depths, which is essential for the success of the technique. Furthermore, additional sensors are required to record soil temperatures in the topmost soil layer. In this study, a new heat-pulse sensor is designed to eliminate these difficulties. The sensor, with four heating needles and 11 temperature needles, is able to monitor the dynamics of soil temperature and thermal properties in the 0-5 cm soil layer. Water evaporation rate from soil is then determined from the measured data on the basis of soil energy balance theory. Laboratory and field experiments will be conducted to evaluate the performance of the new sensor for determining soil profile evaporation.