Faced with the challenges of the energy crisis and climate change, green facades are becoming an increasingly important tool in building architecture. They allow the physical shading of building walls, promote evapotranspiration in summer and increase the thermal insulation in winter. An optimal water and nutrition supply is a fundamental requirement for an effectively working facade greening, which needs appropriate caretaking. In order to keep the use of human resources for maintenance work and the associated costs as low as possible, automatic detection of the plant condition is required. This study provides a remote optical detection method to determine the irrigation condition of plants by measurements of VIS, NIR, and MIR spectra of reflected and emitted radiation by the plant leaves during accelerated senescence. The senescence was accelerated by increased temperature and reduced humidity in a climate chamber, as well as on cut leaves with no water supply. Vegetation indices were investigated with respect to their sensitivity to changes in the plant vitality due to lack of water. An advanced vegetation index trained on time-lapse data was developed, which shows a high sensitivity regarding slight changes in the plant leaf reflectivity and allows conclusions to be drawn about the changes in plant vitality caused by water shortage.
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