Wageningen University & Research, BU Greenhouse Horticulture has an infrared camera which can be used to help to understand plant processes. In the past year, rose buds, anthurium leaves and lilacs and Virbunum were measured with the camera. In addition, measurements were made in greenhouses detect leaks or large temperature deviations. The latter is already widely used in construction business.
When we target an infrared camera to a plant, the camera measures all infrared radiation. This is a sum of infrared radiation (depending on emissivity and temperature), the infrared radiation that is reflected (e.g. direct sunlight) and the transmission (for a leaf, this is low because a leaf absorbs few wavelengths). That ability to deliver or absorb heat is the emissivity of the object and each object has a different emissivity ranging from 0 (theoretically no emission) to 1 (complete emissivity). Asphalt has high emissivity and emits a lot of infrared radiation (nearly equal to the temperature of the asphalt) and absorbs a lot of infrared radiation.
In a greenhouse there are many objects that can affect the infrared measurement, sunlight on a shiny leaf reflects much infrared radiation. Water drops can also reflect. Aluminium benches have low emissivity while rubber pipes, potting soil, black plastic emit a lot of infrared. Certain types of glass have a selective transmission for infrared (speeds up effect of sunlight in heating a greenhouse). Even our presence in the greenhouse can affect the environment, especially at low temperatures.
The young chrysanthemums in the illustration give an example; here, plastic pipes, soil and water droplets on the plants are all visible to the infrared camera. Therefore, cameras must be well oriented and free from disturbing sources to properly measure the temperature of a plant.