Piero Mazzinghi

New vegetation indices for remote measurement of chlorophylls based on leaf directional reflectance spectra

Directional reflectance (R) spectra from 380 to 780 nm for nadir illuminated leaves of four different plants (croton, Codiaeum variegatum; spotted eleagnus, Eleagnus pungens Maculata; Japanese pittosporum, Pittosporum tobira and Benjamin fig, Ficus benjamina Starlight) were acquired at a viewing angle of 30 degrees from the nadir direction. Chlorophyll-a and -b content of leaves covered a range of 1-60 and 0.5-21 microg/cm(2), respectively. In contrast with previous results from hemispherical reflectance measurements, directional reflectance data does not correlate well with chlorophyll concentration. This is mainly due to the external reflectance (R(E)) at the leaf epidermis, caused by the mismatch of the refractive index at the air-epidermis and epidermis-inner layer boundary. The external reflectance can be identified with the blue flat reflectance between 380 and 480 nm. The inner reflectance (R(I)), obtained by subtracting the external reflectance from the measured spectra, was found to be linearly related to the logarithm of the chlorophyll content. Good fitting of the log (Chl) versus R(I)(lambda) curves were obtained for R(I) in the green band (around 550 nm) and close to the inflection point in the red edge (around 700 nm). The coefficient of determination, r(2), of curve fitting improved (up to 0.97) when the normalised inner reflectance NR(I)(lambda)=R(I)(lambda)/R(I)(lambda(0)), with lambda(0)>or=750 nm, was used instead of the absolute reflectance. The best indices for Chl, Chl-a and Chl-b determination were R(I)(542)/R(I)(750), R(I)(706)/R(I)(750) and R(I)(556)/R(I)(750), respectively. However, since the content of Chl-a relative to Chl-b was almost constant for the plants investigated, the two last indices must be further validated on leaves with a high variability in the Chl-a:Chl-b ratio. The error in the determination of chlorophyll content was found to be of the order of 10%. This value was lower than those obtained by applying the vegetation indices previously suggested. Therefore, the normalised inner reflectance in the green and in the red edge represents a more suitable index for the chlorophyll determination than those up to now used.

The F685/F730 Chlorophyll Fluorescence Ratio as a Tool in Plant Physiology: Response to Physiological and Environmental Factors**

Summary The effect of chlorophyll concentration, light intensity and leaf temperature on the chlorophyll fluorescence ratio F685/F730 of intact leaves was evaluated. Fluorescence reabsorption that affects mainly the F685 band increases with chlorophyll concentration. This phenomenon was studied on an aurea mutant of tomato and its wild type, with very different chlorophyll content. Fluorescence spectra of the two genotypes were corrected for reabsorption using their transmittance and reflectance properties. The correction removes most of the differences in the two fluorescence spectra. The F685/F730 decreases during the declining phase of the fluorescence induction kinetics. We demonstrated that when red light is used to induce the fluorescence kinetics the variation of F685/F730 is not due to a change in the leaf absorption, as proved by the simultaneous measurement of leaf transmittance. This evidence suggests that the F685/F730 ratio is sensitive to changes in the photosynthetic activity of the leaf. Under natural conditions, the F685/F730 ratio markedly decreases as light intensity and leaf temperature increase during a daily cycle. This behaviour can be due to photoinhibitory and heat stresses. In controlled laboratory conditions, the F685/F730 ratio was seen to decrease under high light intensity (> 1000 μmol m-2 s-1) at constant leaf temperature. It decreases also when leaf temperature was decreased from 25°C to 14°C at low light intensity (150 μmol m-2 s-1). A possible interpretation of these experimental data relies on a non-negligible contribution of PSI to the total fluorescence at physiological temperatures with respect to - PSII fluorescence. Changes in the photosynthetic activity of the two photosystems may induce variation in the F685/F730 ratio. Our results indicate that light intensity and leaf temperature are important parameters to take into account when the F685/F730 ratio is used as stress indicator.

Remote sensing of chlorophyll a fluorescence of vegetation canopies: 1. Near and far field measurement techniques

Abstract This article presents instruments and techniques, used in several vegetation monitoring experiments. Simultaneous monitoring was performed with different approaches, including fluorescence lidar and passive remote sensing, leaf level reflectance, and laser fluorimetry, and compared with physiological measurements. Most of the instrumentation described was designed and built for this application. Experiments were carried out in the laboratory and in the field, to investigate the relationship between chlorophyll fluorescence spectra and plant ecophysiology. Remote sensing, spectroscopy, and ecophysiology data were then collected by an intensive research team, joining different experiences and working in national and international projects.

Remote sensing of chlorophyll a fluorescence of vegetation canopies: 2. Physiological significance of fluorescence signal in response to environmental stresses☆

Abstract Measurements of laser-induced chlorophyll fluorescence of living leaves were compared to ecophysiological parameters, both in near and far field conditions. Near field measurements were carried out with a two-wavelength portable fluorometer, both in the laboratory and in the field. Results show significant changes of the 690 nm and 730 nm chlorophyll fluorescence bands in different environmental conditions. Water stress and carboxylation limitations also affect the fluorescence spectra. Far field measurements from a ground-operated fluorescence LIDAR system confirm those results. The F690 / F730 fluorescence ratio is then demonstrated as a good index for vegetation remote sensing.

A simple approach to the evaluation of the reabsorption of chlorophyll fluorescence spectra in intact leaves

Abstract A simple approach to the estimation of the effect of reabsorption on chlorophyll fluorescence spectra in intact leaves is reported. It permits one to calculate the chlorophyll fluorescence spectrum effectively emitted inside the leaf using the measured fluorescence spectrum and the total transmittance and reflectance of the leaf. Fluorescence spectra, excited by various laser wavelengths, were measured on leaves of an aurea mutant of tomato and its wild type which differ very much in chlorophyll content and chloroplast ultrastructure. Measured chlorophyll fluorescence spectra for the aurea mutant have higher values of the peak fluorescence ratio F 685 / F 735 ratio of the two fluorescence bands than do the wild type. It is the result of a lower reabsorption effect which affects mainly the shorter-wavelength (685 nm) fluorescence band. The correction for reabsorption removes almost completely the differences between the fluorescence spectra of the two genotypes, confirming the validity of the model. Our work suggests that the evaluation of fluorescence reabsorption must be considered in the widely used methods of vegetation monitoring by chlorophyll fluorescence spectral measurements. It can improve the correlation between fluorescence properties and the physiological state of the plant.

Cleaning processes of encrusted marbles by Nd:YAG lasers operating in free-running and Q-switching regimes.

The removal process of degraded superficial layers from marble samples by Nd:YAG lasers was studied while simulating operative conditions of stone artwork restoration. The effects of laser irradiation at 1064 nm with three different pulse durations of 6 ns, 20 micros, and 200 micros were investigated by time-resolved shadowgraphy and emission spectroscopy of the ejection plume to characterize the specific interaction regimes, with particular concern given to the occurrence of side effects, such as thermal and mechanical damages to the substrate, that could affect the laser cleaning procedure.

The F685/F730 Chlorophyll Fluorescence Ratio as Indicator of Chilling Stress in Plants

Summary The response of chlorophyll fluorescence to chilling temperatures was evaluated by two different experiments. In the first, the F685/F730 and the F v /F m chlorophyll fluorescence ratios were measured in Phaseolus vulgaris L., cv. Mondragone plants under chilling stress at 4 °C and moderate light (100 μmol m -2 s -1 ) up to 72 hours. F v /F m decreased linearly with chilling time indicating a photoinhibitory effect (no change was observed in the dark under the same conditions). F685/F730 underwent a rapid exponential decay followed by a linear slow decline. In a second experiment, the F685/F730 ratio, the total chlorophyll fluorescence, F685 + F730, and the leaf temperature were monitored on a single leaf in a climate chamber as the temperature was decreased from 20 to 4 °C. The experiment was run simultaneously on the chilling-sensitive Phaseolus vulgaris and on the chilling-tolerant Pisum sativum L. (cv. Shuttle) plants. For both species two phases related to the leaf temperature can be distinguished: the first 4-hour period during which the leaf temperature decreased from 24 to 4 °C, and a second period during which the leaf temperature slightly oscillated around 4°C. The behaviour of F685/F730 for the bean was quite different from that of the pea plant. During the first phase, it decreased markedly for the chilling-sensitive bean while a slight increase was observed for the chilling-resistant pea. In the following period, the F685/F730 values for the pea remained constant while those for the bean were found still to decrease. On the basis of our results, the use of the chlorophyll fluorescence ratio as indicator of plant chilling sensitivity can be envisaged.

SMART CLEAN: a new laser system with improved emission characteristics and transmission through long optical fibres

Abstract SMART CLEAN is an innovative Nd:YAG laser system that has been designed to optimize laser cleaning procedures, especially for the treatment of altered stone surfaces. The project, originated by the co-operation of researchers and enterprises involved in optoelectronics system development, was aimed at improving the intrinsic features of the laser source, as well as some practical aspects, in order to facilitate laser application in the restoration yard. Emission characteristics were suitably tailored to obtain effective removal of alteration layers, and to minimize possible side effects. In particular, the pulse duration of the SMART CLEAN laser was set at 20 μs, by means of a proprietary design of the power supply. This was in order to reduce the risk of both mechanical and thermal damage to the artwork substrate, which is more likely to occur with short and long laser pulses, respectively. Moreover, this pulse duration permitted a reliable transmission of high laser energy through long optical fibres (50 m), which allowed easy cleaning operations on facades. The laser system was tested on a large variety of lithotypes and in operative cleaning interventions on Italian monuments.

Performance evaluation of UV sources for lidar fluorosensing of oil films.

A laboratory experiment is discussed which simulates lidar fluorosensing of oil films on the sea surface at UV wavelengths. Three different mixtures of lasing gases, KrF, XeCl and N2 , were used while a fourth wavelength was given by a dye laser. It turns out that films having a thickness as low as 0.01 microm can be detected; the limiting factor resides mainly in the background fluorescence of water. Best results have been obtained with the XeCl excimer laser.

Vegetation Remote-Sensing: A New Field For Lidar Applications

Vegetation remote-sensing is a quite new field for lidar investigations and only few results were shown in litterature. The potential of differential-reflectance and fluorescence lidars in the detection of some plant-characteristics was analyzed with a particular attention to water-stress, senescence and diseas. Both systems showed a good potential in vegetation remote-sensing: differential-reflectance lidars seem particularly interesting for senescence and disease monitoring, while fluorescence lidars seem particularly suitable for water-stress monitoring.