Microwave-based leaf wetness detection in agricultural wireless sensor networks

Leaf wetness monitoring is significant for many agricultural applications, e.g. plant disease prevention. It is strictly related to the appearance of downy mildew, one of the most disruptive plant disease, especially for vine-grapes. Leaf wetness is usually measured using electronic devices, which detect the presence of water on equivalent leaves by measuring the dielectric constant (capacitive sensors) or the electrical resistance (resistive sensors) of their upper surface. Here an alternative solution, suitable for integration into microwave sensor nodes, is presented. The presence of humidity is detected measuring the reflection coefficient of microwave aperture antennas covered with plastic porous film. The feasibility of the solution is proven by some preliminary laboratory measurements.

I. Introduction

Leaf wetness is the measurement of water over leaf surface. The most relevant causes of leaf wetness are rain, guttation, and dew [1]. The analysis of leaf wetness is important for many agricultural and environmental applications: plant disease prevention, atmospheric pollutants monitoring [2]. Duration and quantity of leaf wetness are crucial parameters in plant fungal disease forecasting.