Measuring the dielectric permittivity of a plant canopy and its response to changes in plant water status: An application of Impulse Time Domain Transmission

Impulse Time Domain Transmission (ITDT) has been used to measure the complex dielectric permittivity of media such as ethanol, water and variably saturated sand. This paper applies ITDT to measurements of the complex dielectric permittivity of a vegetation canopy. The dielectric permittivity of a vegetation canopy is very close to that of air and only very small changes in its value will occur with changes in plant water status. This paper presents preliminary results demonstrating that ITDT can make repeatable measurements of the complex components of the dielectric permittivity of a plant canopy. Furthermore, ITDT is shown to be highly sensitive to the very small changes in dielectric that occur as a result of changes in plant water status. Based on these preliminary results, there are potential applications foreseen for ITDT in microwave remote sensing, irrigation scheduling, plant physiological ecology, and fire susceptibility.