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Nowadays there are some experimental data on fluorescence spectra of
various kinds of both healthy vegetation and vegetation in various stressful
situations. These experimental data have been obtained by various authors
using different equipment at different excitation wavelengths (266, 275,
280, 300–400, 308, 325, 327, 337, 340, 355, 360, 380, 395, 396,397, 400,
400–450, 404, 405, 408, 422, 425, 428, 436, 440, 450, 452, 460, 470,
440–500, 480, 488, 500, 515, 525, 532, 535, 550, 590, 600, 627, 630, 633,
635 nm).
The greatest number of the experiments is devoted to the study of plant
fluorescence using lasers (for fluorescence excitation) at wavelengths of
337 (nitrogen laser), 355 and 532 nm (the third and second harmonics of
Nd-YAG laser). A solid-state pulsed laser at a wavelength of 532 nm is
the most promising laser source for designing on-board equipment. It has
the advantage (when developing the equipment for remote sensing) both
over a nitrogen laser at the wavelength of 337 nm (it is better to exploit
solid-state lasers in the on-board equipment), and a laser at the wavelength
of 355 nm (the pulse energy of YAG laser third harmonic is lower than of
the second one) .
It should be also noted, although during the radiation at the wavelength
of 532 nm there is a small chlorophyll absorption in solutions and isolated
chloroplasts, this radiation is efficiently absorbed by plant leaves due to a
complex leaf structure (by virtue of it the optical light paths are significantly
increased as compared with the geometric thickness of the sheet) [17].
In [18] it is shown that despite the low chlorophyll specific absorption
coefficients in this spectral region, the green light is efficiently absorbed
intothe leaf tissue (approximately 80% of the absorption in either red or
blue spectral regions).
Therefore, it is not unusual that there are many publications presenting
the results of the researches into healthy vegetation fluorescence spectra at
the excitation wavelength of 532 nm, is quite large [5–9, 12, 19–22].
However, there are few publications focusing on the research into
plants’ fluorescence spectra in stress situations at the excitation wavelength
of 532 nm [10, 12, 16, 23] (and publications of the same authors based on
the same experimental material in other books).
This article describes the research into a laser method of monitoring
plants’ stress conditions at the fluorescence excitation wavelength of
532 nm. This problem is of pragmatic interest for monitoring some plant
conditions (such as cultivated plants) according to the results of remote
sensing.
Experiment.
In order to measure spectra of laser-induced fluorescence,a
laboratory setup was designed, a block diagram of which is shown in Fig. 1.
72 ISSN 0236-3933. HERALD of the BMSTU. Series “Instrument Engineering”. 2015. No. 2