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Chlorophyll fluorescence parameters derived from MONIPAM and canopy spectral data for Scots pine. MONIPAM parameter were the combined yield of fluorescence and basal thermal energy dissipation (Φ F,D ) and maximum pho- tochemical yield (F v /F m ). AQY values were derived from spectral data.
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- Solar induced chlorophyll a Fluorescence (SIF), which is distributed over a relatively broad (~200 nm) spectral range, is a signal intricately connected to the efficiency of photosynthesis and is now observable from space. Variants of the Fraunhofer Line Depth/Discriminator (FLD) method are used as the basis of retrieval algorithms for estimating...
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... is because the quantum yield of chlorophyll fluorescence is directly controlled by photochemical and non-photochemical energy conversion processes in the photosystems (Porcar-Castell et al., 2014). In the present study we observed a clear increase in apparent spectral yields for all colours, from May to September for pine, which was consistent with the observed increase in the maximum quantum yield of photochemistry (F v / F m ) and chlorophyll fluorescence and basal thermal energy dissipation (Φ F,D ), as measured with a Monitoring PAM system in the same pine canopy (Fig. 4 and Table 1). The increase in F v /F m and Φ F,D from May to September reflects the seasonal dynamics in the acclimation of the light reactions of photosynthesis, where measurements in May were conducted with the canopy still experiencing substantial levels of photosynthetic downregulation (F v /F m = 0.469, Table 1). ...Context 2
... the present study we observed a clear increase in apparent spectral yields for all colours, from May to September for pine, which was consistent with the observed increase in the maximum quantum yield of photochemistry (F v / F m ) and chlorophyll fluorescence and basal thermal energy dissipation (Φ F,D ), as measured with a Monitoring PAM system in the same pine canopy (Fig. 4 and Table 1). The increase in F v /F m and Φ F,D from May to September reflects the seasonal dynamics in the acclimation of the light reactions of photosynthesis, where measurements in May were conducted with the canopy still experiencing substantial levels of photosynthetic downregulation (F v /F m = 0.469, Table 1). Measurements in September were conducted towards the end of the growing season under much smaller downregulation levels (F v /F m = 0.653). ...Citations
... Recently, a new method has emerged to measure nighttime chlorophyll fluorescence spectra of canopies (Atherton et al., 2019;Romero et al., 2018Romero et al., , 2021. Here, light emitting diode (LED) light sources can be utilized to induce chlorophyll fluorescence (LEDIF). ...
... Here, light emitting diode (LED) light sources can be utilized to induce chlorophyll fluorescence (LEDIF). A pure chlorophyll fluorescence signal can be detected by using blue LEDs, which induces chlorophyll fluorescence emissions in the red spectral region, thus the LEDIF signal is unconfounded by spectrally overlapping photosynthetically active radiation region (PAR; 400-700 nm) (Atherton et al., 2019;Romero et al., 2021). A key strength of LEDIF is that it enables dark acclimated measurements of canopy chlorophyll fluorescence, providing inference into vegetation baselines from sustained environmental conditions to assess presence of plant stress impacting fluorescence and potentially, leaf photosynthetic capacity (Rajewicz et al., 2023;Van Wittenberghe et al., 2019). ...
... Both LEDIF Red and LEDIF FR showed similar seasonal declines (Figures 4 and 5). This is likely indicative of both decreasing photosynthetic capacity and chlorophyll content (Atherton et al., 2019;Rajewicz et al., 2023;Romero et al., 2021;Van Wittenberghe et al., 2021). Normalizing LEDIF with LED PAR , which represents changes in reflected radiation, can account for changes in canopy structure due to absorbed photosynthetically active radiation (APAR). ...
The magnitude of chlorophyll fluorescence emission represents both chlorophyll content and energy quenching processes enabling its application to serve as a proxy of photosynthetic activity. Thus, there is interest in advancing methods for canopy‐scale monitoring of chlorophyll fluorescence. Remotely sensed solar‐induced fluorescence (SIF) retrievals offer daytime monitoring of chlorophyll fluorescence, which can serve as an indicator of photosynthesis. However, it represents an instantaneous measurement during the day, which is strongly influenced by incoming radiation, solar angle, and sun/shade fraction—making it difficult to tease out baseline information on plant health and potential photosynthetic capacity—which could be tracked by changes in fluorescence yield (independent of sunlight). Recent advances have demonstrated the potential for inducing nighttime chlorophyll fluorescence via LED light sources at the canopy‐scale, which can be retrieved as LED‐induced chlorophyll fluorescence (LEDIF), potentially serving as a baseline indicator of plant health and photochemical capacity, independent of daytime conditions. In this study, we explored two methods of LEDIF retrievals: (a) hyperspectral sensor (1.33 nm full‐width half max) and (b) low‐cost Red‐Far‐Red photodiode sensor. LEDIF retrieved by the hyperspectral sensor demonstrated strong correlations with daytime SIF and gross primary productivity during mid to end of season phenology (R² > 0.70). In contrast, phenological dynamics of LEDIF retrieved by the photodiode sensor was more subtle, likely due to weaker signal‐to‐noise ratio, but still demonstrated some potential. Overall, LEDIF offers a technique to monitor nighttime chlorophyll fluorescence emissions (and changes in its spectral shape with a hyperspectral sensor) to assess canopy‐scale phenology of photosynthetic potential.
... Romero et al. (2018) successfully used LEDs to measure and model canopy fluorescence and calculate reabsorption values in a controlled plant canopy environment. In a forest consisting of Scots Pine and lingonberry, a coloured (blue, red and green) LED system was installed above the canopies and illuminated the canopy for 2 h (Atherton et al. 2019). In this study, using a field spectrometer at night with long integration times, they measured the quantum yield of fluorescence excited by the LED lights (red, green and blue) and coined the new nocturnal method: LED-Induced chlorophyll a Fluorescence-LEDIF (Atherton et al. 2019). ...
... In a forest consisting of Scots Pine and lingonberry, a coloured (blue, red and green) LED system was installed above the canopies and illuminated the canopy for 2 h (Atherton et al. 2019). In this study, using a field spectrometer at night with long integration times, they measured the quantum yield of fluorescence excited by the LED lights (red, green and blue) and coined the new nocturnal method: LED-Induced chlorophyll a Fluorescence-LEDIF (Atherton et al. 2019). Romero et al. (2021) built an LEDIF system and implemented it in an agricultural environment. ...
... Over the course of one month, we sought to meet two main objectives (1) track changes in canopy-level chlorophyll fluorescence with a new, night-time, low-cost sensor during an imposed stress event and (2) test whether these changes are reflected at the canopy and leaf level. By incorporating the use of LEDs to induce low-light steady-state chlorophyll fluorescence (Atherton et al. 2019) and dovetailing the inexpensive broadband photodiode sensors into our novel platform, we show that a low-cost LED/photodiode platform can be used to track dynamics in canopy fluorescence emission. ...
Chlorophyll fluorescence measured at the leaf scale through pulse amplitude modulation (PAM) has provided valuable insight into photosynthesis. At the canopy- and satellite-scale, solar-induced fluorescence (SIF) provides a method to estimate the photosynthetic activity of plants across spatiotemporal scales. However, retrieving SIF signal remotely requires instruments with high spectral resolution, making it difficult and often expensive to measure canopy-level steady-state chlorophyll fluorescence under natural sunlight. Considering this, we built a novel low-cost photodiode system that retrieves far-red chlorophyll fluorescence emission induced by a blue light emitting diode (LED) light source, for 2 h at night, above the canopy. Our objective was to determine if an active remote sensing-based night-time photodiode method could track changes in canopy-scale LED-induced chlorophyll fluorescence (LEDIF) during an imposed drought on a broadleaf evergreen shrub, Polygala myrtifolia. Far-red LEDIF (720–740 nm) was retrieved using low-cost photodiodes (LEDIFphotodiode) and validated against measurements from a hyperspectral spectroradiometer (LEDIFhyperspectral). To link the LEDIF signal with physiological drought response, we tracked stomatal conductance (gsw) using a porometer, two leaf-level vegetation indices—photochemical reflectance index and normalized difference vegetation index—to represent xanthophyll and chlorophyll pigment dynamics, respectively, and a PAM fluorimeter to measure photochemical and non-photochemical dynamics. Our results demonstrate a similar performance between the photodiode and hyperspectral retrievals of LEDIF (R2 = 0.77). Furthermore, LEDIFphotodiode closely tracked drought responses associated with a decrease in photochemical quenching (R2 = 0.69), Fv/Fm (R2 = 0.59) and leaf-level photochemical reflectance index (R2 = 0.59). Therefore, the low-cost LEDIFphotodiode approach has the potential to be a meaningful indicator of photosynthetic activity at spatial scales greater than an individual leaf and over time.
... The capability to capture distinct signals of plant canopy stress earlier than traditional reflectance-based indices, NDVI and PRI, plus the capability to scale from small to larger canopies holds promise for both research and applications in the lab or field, at night for instance. Recently, two larger scale studies have employed LEDs with spectroscopy at night to study fluorescence responses, one in a forested area examined steady state responses of canopy and understory in a scots pine forest [71] and another used tractor mounted spectrometer and LEDs to measure fluorescence and compare to aerial net primary production among varieties of soybean, both rainfed and irrigated [72]. In the study of soybeans, the authors also show that the F red /F far revealed differences in plant function among cultivars, while traditional RI's did not. ...
Remote sensing offers a non-destructive method to detect plant physiological response to the environment by measuring chlorophyll fluorescence (CF). Most methods to estimate CF require relatively complex retrieval, spectral fitting, or modelling methods. An investigation was undertaken to evaluate measurements of CF using a relatively straightforward technique to detect and monitor plant stress with a spectroradiometer and blue-red light emitting diode (LED). CF spectral response of tomato plants treated with a photosystem inhibitor were assessed and compared to traditional reflectance-based indices: normalized difference vegetation index (NDVI) and photochemical reflectance index (PRI). The blue-red LEDs provided input irradiance and a “window” in the CF emission range of plants (~650 to 850 nm) sufficient to capture distinctive “two-peak” spectra and to distinguish plant health from day to day of the experiment, while within day differences were noisy. CF-based metrics calculated from CF spectra clearly captured signs of vegetation stress earlier than reflectance-based indices and by visual inspection. This CF monitoring technique is a flexible and scalable option for collecting plant function data, especially for indicating early signs of stress. The technique can be applied to a single plant or larger canopies using LED in dark conditions by an individual, or a manned or unmanned vehicle for agricultural or military purposes.
... An understanding of the trade-offs between these processes can be achieved by combining canopy-scale passive (i.e. SIF) with leaf-level active pulse amplitude modulation (PAM) fluorescence techniques; the latter of which can be used to derive parameters such as yields of photochemistry (ϕP) (Genty et al., 1989) and fluorescence (ϕF) (Atherton et al., 2019), and NPQ (Cailly, 1996). Active fluorescence data at high temporal resolution (e.g. ...
Sun‐induced fluorescence in the far‐red region (SIF) is increasingly used as a remote and proximal‐sensing tool capable of tracking vegetation gross primary production (GPP). However, the use of SIF to probe changes in GPP is challenged during extreme climatic events, such as heatwaves.
Here, we examined how the 2018 European heatwave (HW) affected the GPP–SIF relationship in evergreen broadleaved trees with a relatively invariant canopy structure. To do so, we combined canopy‐scale SIF measurements, GPP estimated from an eddy covariance tower, and active pulse amplitude modulation fluorescence.
The HW caused an inversion of the photosynthesis–fluorescence relationship at both the canopy and leaf scales. The highly nonlinear relationship was strongly shaped by nonphotochemical quenching (NPQ), that is, a dissipation mechanism to protect from the adverse effects of high light intensity. During the extreme heat stress, plants experienced a saturation of NPQ, causing a change in the allocation of energy dissipation pathways towards SIF.
Our results show the complex modulation of the NPQ–SIF–GPP relationship at an extreme level of heat stress, which is not completely represented in state‐of‐the‐art coupled radiative transfer and photosynthesis models.
... The accuracy of the disease detection using this technique was further correlated by the results of quantitative polymerase chain reaction. The results demonstrate that such imaging technology holds great potential for large-scale phenotyping and plant stress detection (Wen et al., 2019;Atherton et al., 2019;Liu et al., 2019;Zhang et al., 2019a,b;Porcar-Castell et al., 2021). ...
Diagnostic methods are vital for the study of any kind of infection of forest trees caused by biotic agents. Usually, a combination of traditional and modern verification approaches for plant pathogen identification is often deployed. This is necessary as accurate and proper identification of tree pathogens is critical for a better understanding of disease epidemiology and facilitation of better control and management measures. This chapter discusses the different diagnostic methods currently used to study pathogens causing infections in forest trees focusing primarily on microscopy, immunological, microbiological, biochemical, remote sensing, molecular methods, and sequencing.
... The first time this task was performed, a small Ficus benjamina canopy was irradiated with blue LED light inside a black box (Romero et al., 2018). Atherton et al. (2019) registered the fluorescence emission spectrum distribution of tree crowns and understory in a boreal Scots pine forest. In order to achieve this, they placed a high-power LED array and an ASD spectroradiometer on a platform at approximately 15 m from ground and recorded canopy fluorescence emission at night, with long integration times. ...
... In this work we have presented a novel procedure for measuring Chl fluorescence at canopy level in an active way, tractor-mounted LEDIF. We based our design in our previous work (Romero et al., 2018(Romero et al., , 2020 and the nocturnal LEDIF by Atherton et al. (2019). To our knowledge, this is the first time the full emission spectrum of a crop is observed on . ...
Accurate estimation of aerial net primary production (ANPP) using remotely acquired data is one of the main challenges in both environmental monitoring and precision agriculture. Reflectance-based techniques have been widely used for decades, but detection of fluorescence emission by chlorophyll has emerged as a promising alternative in recent years. Although passive sun-induced fluorescence (SIF) monitoring has shown interesting results, the information it provides is limited to few wavelengths (Fraunhofer and telluric lines). On the other hand, active measurements of steady-state fluorescence and its spectral distribution cover the full-emission spectrum but have not been fully explored due to obvious experimental limitations. In this work we develop a novel active fluorescence measurement procedure, based on lamps and sensors mounted on a field tractor. This technique allowed the detection of the full spectrum of fluorescence emission of a plant crop for the first time in the literature.
The main objective of this work was to analyze how the information based on reflectance and fluorescence, recorded by the new proposed methodology, tracks the differences caused by different irrigation treatments in the ANPP of three soybean varieties. We observed that reflectance-based vegetation indices showed limited sensitivity to these cumulative differences, as only EVI2, NDWI and SRWI were able to distinguish between rainfed and irrigation treatments in some few cases. Passive, irradiance-normalised SIF showed this same trend, but active fluorescence peak ratio (FRed/FFar-red) revealed statistically significant differences for the three cultivars studied. In addition, the latter showed a significant correlation with ANPP for two soybean varieties after correction for light re-absorption and scattering (p < 0.05, R² > 0.5), which was observed for only EVI and foliar water status VIs among passive indicators. Active fluorescence measurements at leaf level by PAM fluorometry did not show differences between treatments in the upper part of the canopy but revealed a biomass-dependent decrease in PSII yield along the vertical axis. Our study demonstrated that fluorescence emission spectrum holds highly valuable information that might allow monitoring ANPP changes upon irrigation from remote sensing applications, and therefore should be carefully studied. Lastly, it highlights the potential of SIF retrieval at both O2-A and O2-B lines.
... There are passive and active methods for the remote sensing of chlorophyll fluorescence. Passive methods measure fluorescence excited directly by sunlight as irradiation source [43], whereas active methods use illumination with artificial light, usually high-energy LASERS or LEDS [44]. ...
... In passive methods, the two signals need to be decoupled using the Fraunhofer line discrimination principle (for detailed information see [45]). A very recent work proposed a new and promising active methodology to measure the chlorophyll fluorescence emission spectral distribution of canopies in situ, upon inducing the fluorescence with light emitting diodes at night [44]. ...
The light that emerges from a biological entity is relevant from many aspects. In the first place, it allows the construction of the organism’s image and consequently it is responsible for visual perception and communication. Secondly, it can become an important tool in obtaining both physiological and chemical information from the observed entity, in a non-destructive way. When an organism is illuminated, the non-absorbed energy emerges as transmitted or reflected light. Additionally, fluorescence, phosphorescence or bioluminescence may be emitted. In our research group, we have studied and modelled the light released as reflectance and fluorescence for different biological systems like flowers, fruits, plant leaves, canopies, bird’s plumage and amphibians. In this review, we present the advances we have made in this area. They range from the development of theoretical approaches to the implementation of optical methodologies for practical applications. The analysis of light interaction with biological material, which is the domain of biophotonics, has recently acquired great importance in view of the increasing use of optical techniques to the study of living tissues. However, the interpretation of the photophysical and spectroscopic properties of these systems is usually complicated by several factors: elevated chromophore’s concentration, optical inhomogeneity, multi-scattering of photons and presence of multi-layered structures in most cases. Because of these, the accurate modelling of the interaction with light helps to avoid artifacts and to better interpret the processes that take place. Physical models used in the analysis of chlorophyll fluorescence in leaves and canopies with application in remote sensing, optical methodologies for food control and quantification of fluorescence in vivo for evaluation of its biological relevance are examples of the use of the emission of light and will be presented in this review.
... Novel approaches for measuring and modeling forest canopy SIF are the objectives in the papers by Atherton et al. (2019) and Liu et al. (2019aLiu et al. ( , 2019b. Atherton et al. (2019) present a method of nocturnal LED-induced fluorescence of chlorophyll a (LEDIF) for measuring canopy SIF spectra at night. ...
... Novel approaches for measuring and modeling forest canopy SIF are the objectives in the papers by Atherton et al. (2019) and Liu et al. (2019aLiu et al. ( , 2019b. Atherton et al. (2019) present a method of nocturnal LED-induced fluorescence of chlorophyll a (LEDIF) for measuring canopy SIF spectra at night. Their LEDIF technique can be used to estimate seasonal changes in spectra of canopy fluorescence, which can potentially derive plant functional dynamics and architectural traits. ...
... Historical and future satellite missions for measuring hyperspectral optical and solar-induced fluorescence of chlorophyll at different spatial and temporal resolutions. et al., 2019), maximum electron transport rate (J max ) (Meacham-Hensold et al., 2019) and Cab (Li et al., 2019; Jay et al., 2019); 3. understanding the potential of Earth observation and proximal sensing to characterize i) variation in plant functional traits in experiments that manipulate global change, such as manipulating nutrients (Pacheco-Labrador et al., 2019), Free-Air CO 2 Enrichment (FACE) experiments (Oberrneier et al., 2019) and phenotyping (Meacham-Hensold et al., 2019) and ii) research into biodiversity and functional diversity (Ma et al., 2019); 4. evaluating and contrasting different methodologies such as i) machine learning vs radiative transfer model inversion (Feret et al., 2019), ii) proof of concept for multiply constrained methods of data assimilation to fully exploit the potential of future satellite SIF, LST and hyperspectral constellations (Pacheco-Labrador et al., 2019) and iii) understanding the impact of spatial autocorrelation on the estimation of plant traits and progress based on machine learning (Rocha et al., 2019); 5. developing new approaches to account for the effects of scattering/re-absorption on SIF within the canopy and to improve our understanding and interpretation of top-of-canopy (TOC) SIF signals for monitoring photosynthetic activity and vegetation stress at landscapeYang et al., 2019) and regional/global(Zeng et al., 2019;Qiu et al., 2019) scales and 6. understanding the dynamics of canopy SIF signals and their controlling factors from ground-based field measurements and modeling(Atherton et al., 2019;Liu et al., 2019aLiu et al., , 2019b, the factors influencing the link between SIF and gross primary production (GPP) at the ecosystem scale and at the landscape scale from airborne-based high-resolution images(Tagliabue et al., 2019). ...
The functions and traits of plants are key to understanding and predicting the adaptation of ecosystems to environmental changes. Remote sensing has been used to monitor the status of vegetation across multiple spatial and temporal scales. The remote sensing of vegetation is now undergoing a paradigm shift from monitoring structural parameters to monitoring functional traits. In particular, recent advances in hyperspectral techniques of remote sensing provide an opportunity to map vegetation traits and functions over a range of scales. In this editorial, we first present the background of the recent advances in the remote sensing of vegetation traits and functions and solar-induced fluorescence (SIF) of chlorophyll. We then summarize eight of the papers in this special issue that focus on new remote-sensing techniques and algorithms developed for retrieving plant functional traits, such as pigment and nitrogen contents and functional parameters. These contributions cover two major scientific themes: (1) estimating and monitoring plant traits and functions and (2) interpreting and understanding remotely sensed SIF signals. The research in this special issue will improve the development of the satellite remote sensing of plant traits and functions, allowing for improved estimation of vegetation processes such as photosynthesis and its associated water and carbon cycles.
... The experimental setup to 607 measure F and Fy here provides a mechanism to observe vegetation under a variety of interesting 608 situations, such as observing F response to plant stresses or to explore cycles of photosynthetic 609 activity throughout the day. This technique would be applicable using UAV or aerial platforms 610 by conducting UAV or aerial spectral measurements at night and scaling up the light source in a 611 manner similar to Atherton et al. (2019). 612 ...
Spectroscopy plays a key role in Earth observations, especially for studies involving vegetation function and structure. These measurements are critical in the context of carbon cycle monitoring from leaf to global scales. Reflectance-based vegetation indices (RIs) have been used extensively in remote sensing studies from the unpiloted aerial vehicle, aerial, and space-based platforms to model quantities related to productivity, such as gross primary production (GPP), while more recently chlorophyll fluorescence (CF) measurements are increasingly exploited to track GPP. CF and RI measurements vary in magnitude, depend on different portions of the spectrum, and are derived from unique equations; thus, instrument uncertainty manifests distinctly for these measurements. Although this is well known, it is often unexamined in experiments and analyses. We use a portable spectroradiometer to make measurements of reflectance-based vegetation indices (RIs) and chlorophyll fluorescence (CF) in order to characterize how measurements of RIs and CF compare to one another. In particular, we examine fluorescence (F) and fluorescence yield (F Yield) under a light-emitting diode grow light (LED), solar-induced fluorescence (SIF), solar-induced fluorescence yield (SIFYield), absorbed photosynthetically active radiation (APAR), and reflectance-based vegetation indices (the normalized difference vegetation index (NDVI), the chlorophyll/carotenoid index (CCI), and the photochemical reflectance index (PRI)) and include maximized propagated uncertainty of the spectroradiometer for each measurement. We show that RIs have a significantly lower propagated error relative to the mean (0.01% to 0.28%) than CF measurements (0.01% to 1.28%) and that while fine resolution spectrometer CF measurements are outside the noise of the instrument and have potential to provide relative measurements of productivity, show why this instrument having fine spectral resolution and sampling is more effective for measurements of APAR and RIs. We also demonstrate that F and F Yield measurements have low propagated uncertainty and propose that future studies of plant function using this spectrometer/LED technique and the full range of spectra be undertaken. Finally, measurements of SIF, F, and APAR can provide estimates of SIFYieldand F Yield in the same order of magnitude, but further examination is required to determine how these measurements compare under a range of illumination and environmental conditions and how they might compare to PRI.
... Due to evident experimental limitations, this passive technique is the most common in studies at canopy level. However, active methods have lately gained particular interest (Atherton et al., 2019). In normal conditions, fluorescence usually represents a very small percentage (between 1 and 5%) of the photons reflected by a vegetation canopy in the red and near-infrared spectrum. ...
... In spite of the difficulties, some groups have managed to register canopy fluorescence spectra using active methods, i.e. exciting chlorophyll with an artificial light source. We accomplished this for the first time in 2018 using a blue LED lamp (Romero et al., 2018) and then Atherton et al. (2019) used a multicolour LED lamp to obtain the emission spectrum of Scots pine in the field. Chlorophyll fluorescence spectrum emitted by vegetation is typically formed by two bands, one in the red (around 685 nm) and another in the far-red (around 735 nm) (Mazzinghi et al., 2002). ...
... Nevertheless, it is the fluorescence yield integrated over the whole spectrum which accounts for the total emitted photons which, in turn, may be linked to photosynthesis and NPQ processes. This has been calculated by radiative transfer model (RTM) simulations (Hernández-Clemente et al., 2017;Celesti et al., 2018) and by direct measures in a very recent work (Atherton et al., 2019), but this has never been corrected taking into account re-absorption processes. ...
The measurement of chlorophyll fluorescence in remote way represents a tool that is becoming increasingly important in relation to the diagnosis of plant health and carbon budget on the planet. However, the detection of this emission is severely affected by distortions, due to processes of light re-absorption both in the leaf and in the canopy. Even though some advances have been made to correct the signal in the far-red, the whole spectral range needs to be addressed, in order to accurately assess plant physiological state. In 2018, we introduced a model to obtain fluorescence spectra at leaf level, from what was observed at canopy level. In this present work, we publish a revision of that physical model, with a more rigorous and exact mathematical treatment. In addition, multiple scattering between the soil and the canopy, and the fraction of land covered by vegetation have also been taken into consideration. We validate this model upon experimental measures, in three types of crops of agronomic interest (Pea, Rye grass and Maize) with different architecture. Our model accurately predicts both the shape of fluorescence spectra at leaf level from that measured at canopy level and the fluorescence ratio. Furthermore, not only do we eliminate artifacts affecting the spectral shape, but we are also able to calculate the quantum yield of fluorescence corrected for re-absorption, from the experimental quantum yield at canopy level. This represents an advance in the study of these systems because it offers the opportunity to make corrections for both the fluorescence ratio and the intensity of the observed fluorescence.
