Plant and Vegetation Monitoring Using Laser-Induced Fluorescence Spectroscopy

This chapter describes the application of laser-induced fluorescence (LIF) spectroscopy to monitoring of living plants. Several applications in agriculture, horticulture, and forestry are described along with specific LIF monitoring systems. The following topics are covered. 1) The basics of LIF spectroscopy for plant monitoring. If an ultraviolet laser is used as an excitation source, the LIF of the plant receiving the light consists of blue-green fluorescence and red-far red fluorescence. Because LIF is a physiologically based optical phenomenon exchanging absorbed optical energy among living molecules, it can include information about living status. 2) A lettuce leaf and a sasanqua (Camellia sasanqua) leaf were monitored using long–term LIF. The growth status of the lettuce was shown by variation in the LIF intensity at 460 nm and 530 nm. Symptoms of water stress in the sasanqua leaf also appeared at the same wavelengths. Such variation can be used for quality control of their products and understanding the process of the development of stress in plants. 3) A laser-induced fluorescence spectrum (LIFS) light detection and ranging (lidar) was developed for monitoring a large tree. The entire LIF spectrum of a zelkova (Zelkova serrata Makino) tree growing outside was monitored at different growth stages. The formation of chlorophyll is discussed. 4) A LIF imaging system and LIFS imaging lidar were developed for laboratory use and for remote monitoring, respectively. LIF images of a spinach leaf indicated plant activity and productivity. The LIFS imaging lidar successfully created a chlorophyll distribution map of a whole poplar tree. The effectiveness of LIF imaging is described. 5) Based on these results, “a Green-Cross; general hospital for plants” and “Optical Farming” are proposed for future development.

Keywords: Laser-induced fluorescence, chlorophyll, photosynthesis, fluorescence spectroscopy, fluorescence lidar, plants, leaf, imaging lidar, agriculture