Remote Laser Fluorimeter to Detect Stress of Plants

Abstract

One of the promising trends in laser monitoring of natural formations is a vegetation control. A variety of reasons such as plant diseases, deficit of moisture or nutrients in the soil, pests of one sort or another, etc. may cause plant stress (conditions under which normal development of plants is impossible). Often (especially at the early stages) to detect these plant stress conditions by appearance is difficult. Therefore, development of remote methods to detect vegetation stress conditions is of relevance. To date, the method based on detection of plant chlorophyll fluorescence is the only method that allows detection of changes in the photosystem of 2 living plants. The overwhelming majority of papers, as a characteristic of the vegetation fluorescence, use a spectrum shape of the fluorescence irradiance, and the stress conditions of plants are defined by the shape distortion of the fluorescence spectra (as compared with vegetation in the normal condition). The paper presents new experimental data on the spectra of laser-induced fluorescence of plants in normal and stressful conditions (due to various reasons). Their analysis allows us to define a technical configuration of the remote laser fluorimeter to detect the vegetation stress conditions. The papers’ analysis shows that to excite laser-induced fluorescence of plants the second harmonic of a pulsed solid-state YAG-Nd laser with a wavelength of 0.532 μm is the most appropriate in terms of hardware implementation. In this case, the excitation wavelength of 0.532 μm is characterized by high (close to maximum) fluorescence excitation efficiency. The results of experimental studies allow us to find the best options of the laser-induced fluorescence irradiance windows for detection of the plant stress conditions. In the most simple implementation, a laser fluorimeter with 0.532 μm excitation wavelength of fluorescence can detect the laser-induced fluorescence irradiance of plants only in two spectral bands with the central wavelengths 0.685 μm and 0.740 μm.