Measuring the layer-average volumetric water content in the uppermost 5 cmof soil using printed circuit board TDR probes

Newly designed printed circuit board TDR probes (PCBPs) were made, and they were calibrated by indoor experiment. A regression equation for estimating the volumetric water content from the dielectric constant measured with th e PCBP was determined, which is almost the same as the well-known Topp's eq uation when the soil is rather wet while the difference becomes larger as t he soil dries. The PCBP was designed to measure the average water content o ver a soil layer 5cm thick because the thickness of soil layer involved in measuring water content by microwave remote sensing is several centimeters. A comparison experiment of measurements with PCBPs and those by microwave remote sensing was conducted in an and area in the northwest of China. The results of this experiment show that the newly designed TDR probe is promis ing as the sensor to get ground truth of the surface wetness. This paper de scribes only the calibration of probes and the observations taken using the m.