A New TDR-Waveform Approach Capable to Measure Soil Moisture Contents at Large Electrical Conductivity Ranges

Wednesday, 17 December 2014
Felipe Cristi Matte, Verónica Fierro, Francisco I Suarez and Jose F. Munoz, Pontifical Catholic University of Chile, Santiago, Chile
Soil moisture is a key parameter in various disciplines, including hydrology, meteorology, agriculture, and mining. Nowadays, there are multiple methods to measure soil moisture. One of the most utilized methods is time domain reflectometry (TDR), which is an indirect method that uses electromagnetic waves to determine the water content of a soil. TDR methods have been widely used because they are non-invasive, easy to use, and have good accuracy in most of the soils. However, a major limitation of current TDR methods lies in the inability to use them in highly conductive saline soils – which are very common in arid and semi-arid regions. TDR methods fail in these soils mainly due to the extremely large signal attenuation along the sensors probes that preclude the detection of the end of the rods, invalidating the use of this methodology. In this work, we propose a new approach to analyze the TDR waveform that enables to use TDR methods at bulk electrical conductivities (BECs) higher than those specified by TDR manufacturers. We assessed the performance of the new approach with a commonly used TDR sensor in sandy soils that had saturated BECs between 1-12 dSm-1. It was found that the traditional methodology it is indeed incapable to estimate soil moisture contents for BECs higher than 4 dSm-1, while the new methodology doubles the actual BEC range with reliable and accurate measures with a maximum error of 6%. These results open a new window of monitoring moisture content in soils where current TDR methods are fairly inaccurate.