TDR Moisture Measurements in Sand-Like Materials: a Comparison between Different Calibration Procedures

Time Domain Reflectometry (TDR) is a well-established technique for the development of microwave sensors devoted to the dielectric characterization of materials. In particular the TDR has become the standard method for measuring soil water content. Although the response of the TDR signal is strictly related to the medium moisture content, it is also affected by several others factors related to the physical and chemical composition of samples and to the characteristics of soil solution. This way, for each test-case, the investigation of specific calibration procedures, plays a crucial role. This paper is focused on the feasibility of the adoption of three calibration procedures, and on the investigation of the most representative empirical and partly deterministic TDR calibration methods for real-time moisture monitoring of sand-like materials.