These sensors detect water on their surface and measure trace amounts of precipitation too small to be detected by a rain gauge, which can detect a minimum of 0.1mm depth.
The surface moisture sensors also indicate the formation of dew, which occurs when the temperature of a surface becomes colder than the dew point of the air. The measurement of surface wetness on leaves is important for disease forecasting in crop plants because fungal and bacterial organisms grow rapidly on wet surfaces. Disease forecasting is based on the number of minutes each day that the surface remains wet. The measurement of surface wetness on roadways and sidewalks can be used to advise when these surfaces become dangerously slippery.
The sensors are highly sensitive to water and are minimally sensitive to ice and snow, thus they do not provide a good indication of snow accumulation.
There are four sensors on this station:
Line Color Sensor Height (m) Orientation of Sensor
Green 1.5 45°
Red 1.5 Horizontal
Dark Blue 0.15 45 °
Light Blue 0.05 Horizontal