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Pablo J Zarcotejada - One of the best experts on this subject based on the ideXlab platform.
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assessing the effects of forest health on sun induced chlorophyll fluorescence using the fluorflight 3 d radiative transfer model to account for forest structure
Remote Sensing of Environment, 2017Co-Authors: Rocio Hernandezclemente, P R J North, Alberto Hornero, Pablo J ZarcotejadaAbstract:Abstract Sun-induced fluorescence (SIF) has been proven to serve as a proxy of photosynthesis activity and therefore, as an early indicator of physiological alterations for global monitoring of vegetation. However, the interpretation of SIF over different spatial resolutions is critical to bridge the existing gap between local and global scales. This study provides insight into the influence of scene components, and forest structure and composition on the quantification of the red and far-red fluorescence signal as an early indicator of forest decLine. The experiments were conducted over an oak forest ( Quercus ilex ) affected by water stress and Phytophthora infection in the southwest of Spain. SIF retrievals through the Fraunhofer Line Depth (FLD) principle with three spectral bands F (FLD3) was assessed using high resolution (60 cm) hyperspectral imagery extracting sunlit crown, full crown and aggregated pixels. Results showed the link between F (FLD3) extracted from sunlit crown pixels and the tree physiological condition in this context of disease infection, yielding significant relationships (r 2 = 0.57, p 2 = 0.63, p 2 = 0.74, p s ). In contrast, a poor relationship was obtained when using aggregated pixels at 30 m spatial resolution, where the relationship between the image-based F (FLD3) and F s yielded a non-significant relationship (r 2 = 0.25, p > 0.05). These results demonstrate the need for methods to accurately retrieve crown SIF from aggregated pixels in heterogeneous forest canopies with large physiological variability among individual trees. This aspect is critical where structural canopy variations and the direct influence of background and shadows affect the SIF amplitude masking the natural variations caused by physiological condition. FluorFLIGHT, a modified version of the three dimensional (3-D) radiative transfer model FLIGHT was developed for this work, enabling the simulation of canopy radiance and reflectance including fluorescence at different spatial resolutions, such as may be derived from proposed satellite missions such as FLEX, and accounting for canopy structure and varying percentage cover. The 3-D modelling approach proposed here significantly improved the relationship between F s and F (FLD3) extracted from aggregated pixels (r 2 = 0.70, p 2 = 0.42, p s ground-data measurements and fluorescence quantum yield estimated with FluorFLIGHT at p 2 = 0.79). The methodology presented here using FluorFLIGHT also demonstrated its capabilities for mapping SIF at the tree level for single tree assessment of forest physiological condition in the context of early disease detection.
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seasonal stability of chlorophyll fluorescence quantified from airborne hyperspectral imagery as an indicator of net photosynthesis in the context of precision agriculture
Remote Sensing of Environment, 2016Co-Authors: Pablo J Zarcotejada, M V Gonzalezdugo, E FereresAbstract:Abstract The seasonal stability of solar-induced chlorophyll fluorescence (SIF) vs field-measured leaf CO2 assimilation (A) was assessed over a period of 2 years by means of airborne flights performed at midday and diurnally over a citrus (evergreen) crop canopy. The orchard was cultivated under a control treatment (ET) that received 100% of its water requirements and two regulated deficit irrigation (RDI) treatments with water supply reduced to 37% and 50% of the control level during the summer. Field measurements consisted of assimilation rate, stomatal conductance, stem water potential, leaf fluorescence and leaf reflectance. The airborne campaigns took place in 2012 and 2013, and were flown on the solar plane in order to acquire hyperspectral imagery at 40 cm resolution, 260 spectral bands and 1.85 nm/pixels in the 400–885 nm spectral region. A thermal camera was installed in tandem in all flights, acquiring imagery in the 7.5–13 μm spectral region at 640 × 480 pixel resolution, yielding a 50 cm pixel size. The robustness of the SIF quantification through the Fraunhofer Line Depth (FLD) principle based on three spectral bands (FLD3), as well as the performance of physiological and structural hyperspectral indices, was evaluated in order to understand their ability to track photosynthesis at different phenological and stress stages throughout the season. Solar induced fluorescence quantified as FLD3 was the most robust indicator of photosynthesis in all the airborne campaigns performed in the course of the two-year experiment, which comprised seven midday flights and two diurnals. The relationships between fluorescence (FLD3) and assimilation rates yielded correlation coefficients (R) between 0.64 and 0.82 across all dates, these being statistically significant with p-values between p
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relationships between net photosynthesis and steady state chlorophyll fluorescence retrieved from airborne hyperspectral imagery
Remote Sensing of Environment, 2013Co-Authors: Pablo J Zarcotejada, A Catalina, M R Gonzalez, Pedro Jesus Jimenez MartinAbstract:Abstract Previous studies have demonstrated the link between leaf chlorophyll fluorescence and photosynthesis, mainly at the leaf level and under controlled laboratory conditions. The present study makes progress in demonstrating the relationship between steady-state fluorescence and net photosynthesis measured under natural light field conditions both at the leaf and image levels. Ground measurements and airborne campaigns were conducted over two summers to acquire hyperspectral imagery at 40 cm resolution and 260 spectral bands in the 400–885 nm spectral region. This enabled the identification of pure vegetation pixels to extract their radiance spectra. The datasets were collected in August 2010 and 2011 in the western part of the area included in the Ribera del Duero Designation of Origin (Denominacion de Origen), in northern Spain. The experiments were conducted in twelve full production vineyards where two study plots per field were selected to ensure adequate variability in leaf biochemistry and physiological condition. The vineyard fields were selected on the basis of their gradient in leaf nutrition and plant water status and showed variability in leaf pigment values and stomatal conductance. Leaves were collected for destructive sampling and biochemical determination of chlorophyll a + b, carotenoids and anthocyanins in the laboratory. Leaf steady-state and dark-adapted fluorescence parameters, net photosynthesis (Pn) and stomatal conductance (Gs) were measured in the field under natural light conditions. Such data were used as a validation dataset to assess fluorescence–photosynthesis relationships both at the leaf and the image level. The Fraunhofer Line Depth (FLD) principle based on three spectral bands (FLD3) was the method used to quantify fluorescence emission from radiance spectra extracted from pure vegetation pixels identified in the hyperspectral imagery. Fluorescence retrievals conducted using the FLD3 method yielded significant results when compared to ground-measured steady-state Fs (r2 = 0.48; p
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fluorescence temperature and narrow band indices acquired from a uav platform for water stress detection using a micro hyperspectral imager and a thermal camera
Remote Sensing of Environment, 2012Co-Authors: Pablo J Zarcotejada, Victoria Gonzalezdugo, J A J BerniAbstract:article i nfo The remote detection of water stress in a citrus orchard was investigated using leaf-level measurements of chlorophyll fluorescence and Photochemical Reflectance Index (PRI) data, seasonal time-series of crown tem- perature and PRI, and high-resolution airborne imagery. The work was conducted in an orchard where a reg- ulated deficit irrigation (RDI) experiment generated a gradient in water stress levels. Stomatal conductance (Gs) and water potential (Ψ) were measured over the season on each treatment block. The airborne data consisted on thermal and hyperspectral imagery acquired at the time of maximum stress differences among treatments, prior to the re-watering phase, using a miniaturized thermal camera and a micro-hyperspectral imager on board an unmanned aerial vehicle (UAV). The hyperspectral imagery was acquired at 40 cm resolution and 260 spectral bands in the 400-885 nm spectral range at 6.4 nm full width at half maximum (FWHM) spectral resolution and 1.85 nmsampling interval,enablingthe identificationof pure crownsfor extractingradiance andreflectance hyperspectral spectra from each tree. The FluorMOD model was used to investigate the retrieval of chlorophyll fluorescence by applying the Fraunhofer Line Depth (FLD) principle using three spectral bands (FLD3), which demonstrated that fluorescence retrievalwas feasible with the configuration of the UAV micro-hyperspectral in- strument flown over the orchard. Results demonstrated the link between seasonal PRI and crown temperature acquired from instrumented trees and field measurements of stomatal conductance and water potential. The sensitivity of PRI and Tc-Ta time-series to water stress levels demonstrated a time delay of PRI vs Tc-Ta during the recovery phase after re-watering started. At the time of the maximum stress difference among treatment blocks, the airborneimagery acquired fromthe UAV platform demonstrated that the crown temperature yielded the best coefficient of determination for Gs (r 2
Michele Meroni - One of the best experts on this subject based on the ideXlab platform.
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modeling the impact of spectral sensor configurations on the fld retrieval accuracy of sun induced chlorophyll fluorescence
Remote Sensing of Environment, 2011Co-Authors: Alexander Damm, Andre Erler, Walter Hillen, Michele Meroni, Michael E Schaepman, Wout Verhoef, Uwe RascherAbstract:Abstract Chlorophyll fluorescence is related to photosynthesis and can serve as a remote sensing proxy for estimating photosynthetic energy conversion and carbon uptake. Recent advances in sensor technology allow remote measurements of the sun-induced chlorophyll fluorescence signal (Fs) at leaf and canopy scale. The commonly used Fraunhofer Line Depth (FLD) principle exploits spectrally narrow atmospheric oxygen absorption bands and relates Fs to the difference of the absorption feature depth of a fluorescensing and a non-fluorescensing surface. However, due to the nature of these narrow bands, Fs retrieval results depend not only on vegetation species type or environmental conditions, but also on instrument technology and processing algorithms. Thus, an evaluation of all influencing factors and their separate quantification is required to further improve Fs retrieval and to allow a reproducible interpretation of Fs signals. Here we present a modeling study that isolates and quantifies the impacts of sensor characteristics, such as spectral sampling interval (SSI), spectral resolution (SR), signal to noise ratio (SNR), and spectral shift (SS) on the accuracy of Fs measurements in the oxygen A band centered at 760 nm (O 2 -A). Modeled high resolution radiance spectra associated with known Fs were spectrally resampled, taking into consideration the various sensor properties. Fs was retrieved using the three most common FLD retrieval methods, namely the original FLD method (sFLD), the modified FLD (3FLD) and the improved FLD (iFLD). The analysis investigates parameter ranges, which are representative for field and airborne instruments currently used in Fs research (e.g., ASD FieldSpec, OceanOptics HR, AirFLEX, AISA, APEX, CASI, and MERIS). Our results show that the most important parameter affecting the retrieval accuracy is SNR, SR accounts for ≤ 40% of the error, the SSI for ≤ 12%, and SS for ≤ 7% of the error. A trade-off study revealed that high SR can partly compensate for low SNR. There is a strong interrelation between all parameters and the impact of specific parameters can compensate or amplify the influence of others. Hence, the combination of all parameters must be considered by the evaluation of sensors and their potential for Fs retrieval. In general, the standard FLD method strongly overestimates Fs, while 3FLD and iFLD provide a more accurate estimation of Fs. We conclude that technical sensor specifications and the retrieval methods cause a significant variability in retrieved Fs signals. Results are intended to be one relevant component of the total uncertainty budget of Fs retrieval and have to be considered in the interpretation of retrieved Fs signals.
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performance of spectral fitting methods for vegetation fluorescence quantification
Remote Sensing of Environment, 2010Co-Authors: Michele Meroni, Jose Moreno, Lorenzo Busetto, Roberto Colombo, Luis Guanter, Wout VerhoefAbstract:Abstract The Fraunhofer Line Discriminator (FLD) principle has long been considered as the reference method to quantify solar-induced chlorophyll fluorescence (F) from passive remote sensing measurements. Recently, alternative retrieval algorithms based on the spectral fitting of hyperspectral radiance observations, Spectral Fitting Methods (SFMs), have been proposed. The aim of this manuscript is to investigate the performance of such algorithms and to provide relevant information regarding their use. FLD and SFMs were used to estimate F starting from Top Of Canopy (TOC) fluxes at very high spectral resolution (0.12 nm) and sampling interval (0.1 nm), exploiting the O2-B (687.0 nm) and O2-A (760.6 nm) atmospheric oxygen absorption bands overlapping the fluorescence emissions at the red and far-red spectral window. Specific parameters affecting FLD and SFM performances are investigated and the accuracy of F estimation of the two methods is compared. The problem related to the lack of independent measurements of F at canopy level, which prevents the direct assessment of F estimation accuracy with actual measurements, is overcome in this study by using a modeled database of TOC reflectance spectra. In order to compute accuracy figures valid for operative applications the simulated spectra were perturbed by the addition of radiometric noise. An investigation was conducted to determine the best FLD channel configuration; it showed that violation of FLD assumptions results in a positive bias in F estimation at both oxygen absorption bands that cannot be avoided even at the high spectral resolution considered. SFMs were shown to be more accurate than FLD under any noise configuration considered.
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leaf level detection of solar induced chlorophyll fluorescence by means of a subnanometer resolution spectroradiometer
Remote Sensing of Environment, 2006Co-Authors: Michele Meroni, Roberto ColomboAbstract:A leaf level investigation on the spectral signature of Phaseolus vulgaris was undertaken by using a very high spectral resolution spectroradiometer featuring full width at half maximum of 0.06 nm and spectral range of 635.5–802.5 nm. High spectral resolution allows detection of leaf reflected and emitted radiance fields in two narrow absorption bands at 687 and 760 nm, respectively, where solar irradiance is strongly reduced owing to molecular oxygen absorption of the terrestrial atmosphere. The flux emitted due to chlorophyll fluorescence was measured using the Fraunhofer Line depth principle by spectrally modelling the signal, capitalizing on the high resolution of the spectroradiometer devices. An experiment was conducted on two potted bean plants. One was maintained in good health for use as a reference while the other was treated with a photosystem II inhibitor. Collected spectra show that the fluorescence emission produces a pair of characteristic peaks superimposed on the typical leaf-specific reflectance curve. The magnitude of the fluorescence signal of the herbicide-treated leaf was four times greater than that of the control plant, thus indicating damage to the photosynthetic apparatus of the plant.
Roberto Colombo - One of the best experts on this subject based on the ideXlab platform.
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sun induced fluorescence a new probe of photosynthesis first maps from the imaging spectrometer hyplant
Global Change Biology, 2015Co-Authors: Uwe Rascher, Alexander Damm, Roberto Colombo, Luis Guanter, Luis Alonso, Andreas Burkart, C Cilia, S Cogliati, M Drusch, Jan HanusAbstract:Variations in photosynthesis still cause substantial uncertainties in predicting photosynthetic CO2 uptake rates and monitoring plant stress. Changes in actual photosynthesis that are not related to greenness of vegetation are difficult to measure by reflectance based optical remote sensing techniques. Several activities are underway to evaluate the sun-induced fluorescence signal on the ground and on a coarse spatial scale using space-borne imaging spectrometers. Intermediate-scale observations using airborne-based imaging spectroscopy, which are critical to bridge the existing gap between small-scale field studies and global observations, are still insufficient. Here we present the first validated maps of sun-induced fluorescence in that critical, intermediate spatial resolution, employing the novel airborne imaging spectrometer HyPlant. HyPlant has an unprecedented spectral resolution, which allows for the first time quantifying sun-induced fluorescence fluxes in physical units according to the Fraunhofer Line Depth Principle that exploits solar and atmospheric absorption bands. Maps of sun-induced fluorescence show a large spatial variability between different vegetation types, which complement classical remote sensing approaches. Different crop types largely differ in emitting fluorescence that additionally changes within the seasonal cycle and thus may be related to the seasonal activation and deactivation of the photosynthetic machinery. We argue that sun-induced fluorescence emission is related to two processes: (i) the total absorbed radiation by photosynthetically active chlorophyll; and (ii) the functional status of actual photosynthesis and vegetation stress.
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performance of spectral fitting methods for vegetation fluorescence quantification
Remote Sensing of Environment, 2010Co-Authors: Michele Meroni, Jose Moreno, Lorenzo Busetto, Roberto Colombo, Luis Guanter, Wout VerhoefAbstract:Abstract The Fraunhofer Line Discriminator (FLD) principle has long been considered as the reference method to quantify solar-induced chlorophyll fluorescence (F) from passive remote sensing measurements. Recently, alternative retrieval algorithms based on the spectral fitting of hyperspectral radiance observations, Spectral Fitting Methods (SFMs), have been proposed. The aim of this manuscript is to investigate the performance of such algorithms and to provide relevant information regarding their use. FLD and SFMs were used to estimate F starting from Top Of Canopy (TOC) fluxes at very high spectral resolution (0.12 nm) and sampling interval (0.1 nm), exploiting the O2-B (687.0 nm) and O2-A (760.6 nm) atmospheric oxygen absorption bands overlapping the fluorescence emissions at the red and far-red spectral window. Specific parameters affecting FLD and SFM performances are investigated and the accuracy of F estimation of the two methods is compared. The problem related to the lack of independent measurements of F at canopy level, which prevents the direct assessment of F estimation accuracy with actual measurements, is overcome in this study by using a modeled database of TOC reflectance spectra. In order to compute accuracy figures valid for operative applications the simulated spectra were perturbed by the addition of radiometric noise. An investigation was conducted to determine the best FLD channel configuration; it showed that violation of FLD assumptions results in a positive bias in F estimation at both oxygen absorption bands that cannot be avoided even at the high spectral resolution considered. SFMs were shown to be more accurate than FLD under any noise configuration considered.
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leaf level detection of solar induced chlorophyll fluorescence by means of a subnanometer resolution spectroradiometer
Remote Sensing of Environment, 2006Co-Authors: Michele Meroni, Roberto ColomboAbstract:A leaf level investigation on the spectral signature of Phaseolus vulgaris was undertaken by using a very high spectral resolution spectroradiometer featuring full width at half maximum of 0.06 nm and spectral range of 635.5–802.5 nm. High spectral resolution allows detection of leaf reflected and emitted radiance fields in two narrow absorption bands at 687 and 760 nm, respectively, where solar irradiance is strongly reduced owing to molecular oxygen absorption of the terrestrial atmosphere. The flux emitted due to chlorophyll fluorescence was measured using the Fraunhofer Line depth principle by spectrally modelling the signal, capitalizing on the high resolution of the spectroradiometer devices. An experiment was conducted on two potted bean plants. One was maintained in good health for use as a reference while the other was treated with a photosystem II inhibitor. Collected spectra show that the fluorescence emission produces a pair of characteristic peaks superimposed on the typical leaf-specific reflectance curve. The magnitude of the fluorescence signal of the herbicide-treated leaf was four times greater than that of the control plant, thus indicating damage to the photosynthetic apparatus of the plant.
R J Reynolds - One of the best experts on this subject based on the ideXlab platform.
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dynamical zodiacal cloud models constrained by high resolution spectroscopy of the zodiacal light
Icarus, 2008Co-Authors: S I Ipatov, A. Kutyrev, G J Madsen, John C Mather, Harvey S Moseley, R J ReynoldsAbstract:Abstract The simulated Doppler shifts of the solar Mg I Fraunhofer Line produced by scattering on the solar light by asteroidal, cometary, and trans-neptunian dust particles are compared with the shifts obtained by Wisconsin H-Alpha Mapper (WHAM) spectrometer. The simulated spectra are based on the results of integrations of the orbital evolution of particles under the gravitational influence of planets, the Poynting–Robertson drag, radiation pressure, and solar wind drag. Our results demonstrate that the differences in the Line centroid position in the solar elongation and in the Line width averaged over the elongations for different sizes of particles are usually less than those for different sources of dust. The deviation of the derived spectral parameters for various sources of dust used in the model reached maximum at the elongation (measured eastward from the Sun) between 90° and 120°. For the future zodiacal light Doppler shifts measurements, it is important to pay a particular attention to observing at this elongation range. At the elongations of the fields observed by WHAM, the model-predicted Doppler shifts were close to each other for several scattering functions considered. Therefore the main conclusions of our paper do not depend on a scattering function and mass distribution of particles if they are reasonable. A comparison of the dependencies of the Doppler shifts on solar elongation and the mean width of the Mg I Line modeled for different sources of dust with those obtained from the WHAM observations shows that the fraction of cometary particles in zodiacal dust is significant and can be dominant. Cometary particles originating inside Jupiter's orbit and particles originating beyond Jupiter's orbit (including trans-neptunian dust particles) can contribute to zodiacal dust about 1/3 each, with a possible deviation from 1/3 up to 0.1–0.2. The fraction of asteroidal dust is estimated to be ∼0.3–0.5. The mean eccentricities of zodiacal particles located at 1–2 AU from the Sun that better fit the WHAM observations are between 0.2 and 0.5, with a more probable value of about 0.3.
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dynamical zodiacal cloud models constrained by high resolution spectroscopy of the zodiacal light
36th Annual Lunar and Planetary Science Conference, 2005Co-Authors: S I Ipatov, S H Moseley, A. Kutyrev, G J Madsen, John C Mather, R J ReynoldsAbstract:We present simulated observations of the Doppler shifts of the solar Mg I Fraunhofer Line scattered by asteroidal, cometary, and trans-Neptunian dust particles. The studies are based on the results of integrations of orbital evolution of particles under the gravitational influence of planets, the Poynting-Robertson drag, radiation pressure, and solar wind drag. The derived shifts in the centroid and profile of the Line with solar elongation are different for different sources of dust. A comparison of the velocities of zodiacal dust particles based on these numerical integrations with the velocities obtained from WHAM observations shows that the fraction of cometary dust particles among zodiacal dust particles is significant and can be dominant. A considerable fraction of trans-Neptunian dust particles among zodiacal dust particles also fits different observations. The mean eccentricity of zodiacal dust particles is estimated to be about 0.5.
Uwe Rascher - One of the best experts on this subject based on the ideXlab platform.
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DERIVING SUN-INDUCED CHLOROPHYLL FLUORESCENCE FROM AIRBORNE BASED SPECTROMETER DATA
2020Co-Authors: Alexander Damm, Michael E Schaepman, Anke Schickling, Daniel Schläpfer, Uwe RascherAbstract:ABSTRACT Sun-induced chlorophyll fluorescence (Fs) is a promising parameter for remote measuring plant photosynthesis. It has been demonstrated that Fs at cell and leaf level is strongly related to photosynthesis. The transfer of the Fs approach to canopy level remains challenging as the canopy Fs signal is not fully understood yet. Several factors influence the Fs signal and need to be quantified. However, the absence of dedicated imaging spectrometers limits the experimental data for such investigations. We propose an experimental setup allowing spatio-temporal investigations of canopy Fs. A non-imaging spectrometer was installed in a low-flying aircraft. An agricultural area was continuously monitored including the extensive coverage of dedicated fields. Fs was retrieved from spectrometer data using the FLD (Fraunhofer Line Depth) method combined with simulated (MODTRAN-4) at-sensor radiances of a reference surface. We present the methodological framework to derive canopy chlorophyll fluorescence from airborne based non-imaging spectrometer measurements and a quality assessment of the data
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sun induced fluorescence a new probe of photosynthesis first maps from the imaging spectrometer hyplant
Global Change Biology, 2015Co-Authors: Uwe Rascher, Alexander Damm, Roberto Colombo, Luis Guanter, Luis Alonso, Andreas Burkart, C Cilia, S Cogliati, M Drusch, Jan HanusAbstract:Variations in photosynthesis still cause substantial uncertainties in predicting photosynthetic CO2 uptake rates and monitoring plant stress. Changes in actual photosynthesis that are not related to greenness of vegetation are difficult to measure by reflectance based optical remote sensing techniques. Several activities are underway to evaluate the sun-induced fluorescence signal on the ground and on a coarse spatial scale using space-borne imaging spectrometers. Intermediate-scale observations using airborne-based imaging spectroscopy, which are critical to bridge the existing gap between small-scale field studies and global observations, are still insufficient. Here we present the first validated maps of sun-induced fluorescence in that critical, intermediate spatial resolution, employing the novel airborne imaging spectrometer HyPlant. HyPlant has an unprecedented spectral resolution, which allows for the first time quantifying sun-induced fluorescence fluxes in physical units according to the Fraunhofer Line Depth Principle that exploits solar and atmospheric absorption bands. Maps of sun-induced fluorescence show a large spatial variability between different vegetation types, which complement classical remote sensing approaches. Different crop types largely differ in emitting fluorescence that additionally changes within the seasonal cycle and thus may be related to the seasonal activation and deactivation of the photosynthetic machinery. We argue that sun-induced fluorescence emission is related to two processes: (i) the total absorbed radiation by photosynthetically active chlorophyll; and (ii) the functional status of actual photosynthesis and vegetation stress.
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modeling the impact of spectral sensor configurations on the fld retrieval accuracy of sun induced chlorophyll fluorescence
Remote Sensing of Environment, 2011Co-Authors: Alexander Damm, Andre Erler, Walter Hillen, Michele Meroni, Michael E Schaepman, Wout Verhoef, Uwe RascherAbstract:Abstract Chlorophyll fluorescence is related to photosynthesis and can serve as a remote sensing proxy for estimating photosynthetic energy conversion and carbon uptake. Recent advances in sensor technology allow remote measurements of the sun-induced chlorophyll fluorescence signal (Fs) at leaf and canopy scale. The commonly used Fraunhofer Line Depth (FLD) principle exploits spectrally narrow atmospheric oxygen absorption bands and relates Fs to the difference of the absorption feature depth of a fluorescensing and a non-fluorescensing surface. However, due to the nature of these narrow bands, Fs retrieval results depend not only on vegetation species type or environmental conditions, but also on instrument technology and processing algorithms. Thus, an evaluation of all influencing factors and their separate quantification is required to further improve Fs retrieval and to allow a reproducible interpretation of Fs signals. Here we present a modeling study that isolates and quantifies the impacts of sensor characteristics, such as spectral sampling interval (SSI), spectral resolution (SR), signal to noise ratio (SNR), and spectral shift (SS) on the accuracy of Fs measurements in the oxygen A band centered at 760 nm (O 2 -A). Modeled high resolution radiance spectra associated with known Fs were spectrally resampled, taking into consideration the various sensor properties. Fs was retrieved using the three most common FLD retrieval methods, namely the original FLD method (sFLD), the modified FLD (3FLD) and the improved FLD (iFLD). The analysis investigates parameter ranges, which are representative for field and airborne instruments currently used in Fs research (e.g., ASD FieldSpec, OceanOptics HR, AirFLEX, AISA, APEX, CASI, and MERIS). Our results show that the most important parameter affecting the retrieval accuracy is SNR, SR accounts for ≤ 40% of the error, the SSI for ≤ 12%, and SS for ≤ 7% of the error. A trade-off study revealed that high SR can partly compensate for low SNR. There is a strong interrelation between all parameters and the impact of specific parameters can compensate or amplify the influence of others. Hence, the combination of all parameters must be considered by the evaluation of sensors and their potential for Fs retrieval. In general, the standard FLD method strongly overestimates Fs, while 3FLD and iFLD provide a more accurate estimation of Fs. We conclude that technical sensor specifications and the retrieval methods cause a significant variability in retrieved Fs signals. Results are intended to be one relevant component of the total uncertainty budget of Fs retrieval and have to be considered in the interpretation of retrieved Fs signals.
