Comparative study of moisture measurements by time domain transmissometry

Time domain transmissometry (TDT) is an emerging technology in the field of moisture measurements. While time domain reflectometry (TDR) is a well-known method for moisture measurements since the 1980s, TDT measurements were not applied until the last decade. The key benefit of TDT measurements is the robustness against multiple reflections along the sensor resulting in higher measurement accuracy and lower requirements concerning the electronics. However, transmission measurements in soil, grain, or other bulky goods yield some difficulties. Especially the realization of a second measuring port at the end of the sensor is challenging. This contribution gives an overview on TDT systems for moisture measurements. Beside the theoretical background, existing sensors and measurement systems are compared and illustrated in detail.