Leaf Wetness Sensors Definitive Guide For 2022

Leaf wetness is a meteorological parameter that describes the amount of dew and precipitation left on surfaces. It is used for monitoring leaf moisture for agriculturalpurposes, such as fungus and disease control, for control of irrigation systems, and for detection of fog and dew conditions, and early detection of rainfall.^[1]

Leaf wetness may be measured by various means:^[2][3]

• By change in electrical resistance between two metal conductors in an alternate finger^[4] or double spiral^[5] configuration on a flat surface, either flat or cylindrical.^[6] The conductors are usually gold plated for corrosion resistance. An issue with this method is that measurements depend on droplets being large enough to bridge the gap between the conductors. A surface coating of for instance hygroscopic latex paint may be applied for more consistent results.^[7][8][9]Resistance measurement is often by alternating current excitation.^[10]
• By measuring the change in the dielectric constant of the surface of a sensor, thus detecting the presence of water or ice on the sensor’s surface.^[11]
• A sensor with hygroscopic properties where a change in sensor length or weight can be measured mechanically.

Electrical resistivity (also known as specific electrical resistance, or volume resistivity) is a fundamental property of a material that quantifies how strongly that material opposes the flow of electric current. A low resistivity indicates a material that readily allows the flow of electric current. Resistivity is commonly represented by the Greek letter ρ (rho). The SI unit of electrical resistivity is the ohm–metre (Ω⋅m).^[1][2][3] As an example, if a 1 m × 1 m × 1 m solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is 1 Ω, then the resistivity of the material is 1 Ω⋅m.

Electrical conductivity or specific conductance is the reciprocal of electrical resistivity, and measures a material’s ability to conduct an electric current. It is commonly represented by the Greek letter σ (sigma), but κ (kappa) (especially in electrical engineering) or γ (gamma) are also occasionally used. Its SI unit is siemens per metre (S/m).