Instruments and methods of measurement laser method for vegetation monitoring

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In Fig. 5 it can be seen that the impact of the stress factor (in this
case caused by the excessive amount of water when watering) gradually
accumulates, with increasing the time of incorrect plant watering. It can
manifest itself both in changing the spectrum form and increasing the
fluorescence level simultaneously. In the figure, the measured fluorescence
levels of the plants under stress (curve 3) are significantly above the
fluorescence level of the plants in good conditions. Moreover, the ratio
of fluorescence intensities R680 /740 at the wavelengths of 680 and 740 nm
for the plant under stress is greater than unity, and the value R680/740 for
the plant in a normal condition is less than unity.
The experimental results show the application perspectiveness of the
laser fluorescence method for monitoring the plant conditions using the
fluorescence excitation wavelength of 532 nm. Such monitoring can be
implemented using an UAV and airborne laser fluorometer. Objective
information that may be remotely obtained by the onboard laser fluorometer
is a form of the fluorescence spectrum and the relative fluorescence intensity
of the test site (for example, cultivated plant fields). Since the fluorescence
of soil is much less than the fluorescence of vegetation (it can be seen from
the data experimentally obtained both by the authors of this paper and by
other authors), the measured fluorescence spectrumform and fluorescence
intensity will specifically characterize the vegetation.
Conclusions. Thus, the experimental studies of plants’ laser-induced
fluorescence at the excitation wavelength of 532 nm indicate that the impact
of the stress factors on plants caused by the presence of contaminants in
the soil, an excess amount of water or mechanical damage, significantly
distorts the plant fluorescence spectra. The influence of the stress factor can
manifest itself in either a modified form of the fluorescence spectrum (the
ratio of fluorescence intensities at the two wavelengths of 680 and 740 nm
is the identifying factor), or a change in the fluorescence level that can be
used as the basis of the laser method of monitoring the plant conditions.
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ISSN 0236-3933. HERALD of the BMSTU. Series “Instrument Engineering”. 2015. No. 2 77