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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Power and Difference of the Up-and-Downward Sun-Induced Chlorophyll Fluorescence on Detecting Leaf Nitrogen Content in Wheat at the Leaf Scale
摘要： Leaf nitrogen content (LNC) can be used to diagnose the nutritional status and guide precise fertilization. Numerous previous researchers estimated LNC on reflectance spectrum or active chlorophyll fluorescence techniques with certain limitations. This study proposed a new technique of sun-induced chlorophyll fluorescence (SIF) for detecting LNC. We conducted an experiment to determine the optimal measurement point at the leaf scale for SIF and the best fluorescence yield indices (FY indices) extracted from SIF for LNC detection. The differences of the upward and downward FY indices were compared to determine the optimal FY indices. The results showed that the 1/3 distance from the leaf base is the optimal position for measuring SIF at the leaf level, and the downward FY indices are much better than the upward one with ratio peak FY687/FY739 as the best to monitor the LNC. The findings demonstrated that SIF can be utilized as a potential method for monitoring the LNC of winter wheat with higher efficiency.
关键词： ↓FY687/FY739,leaf nitrogen (LNC),upward and downward,fluorescence yield indices (FY indices),sun-induced chlorophyll fluorescence (SIF)
更新于2025-09-09 09:28:46
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Using reflectance to explain vegetation biochemical and structural effects on sun-induced chlorophyll fluorescence
摘要： The growing availability of global measurements of sun-induced chlorophyll fluorescence (SIF) can help in improving crop monitoring, especially the monitoring of photosynthetic activity. However, variations in top-of-canopy (TOC) SIF cannot be directly interpreted as physiological changes because of the confounding effects of vegetation biochemistry (i.e. pigments, dry matter and water) and structure. In this study, we propose an approach of using radiative transfer models (RTMs) and TOC reflectance to estimate the biochemical and structural effects on TOC SIF, as a necessary step in retrieving physiological information from TOC SIF. The approach was assessed by using airborne (HyPlant) reflectance and SIF data acquired over an agricultural experimental farm in Germany on two days, before and during a heat event in summer 2015 with maximum temperatures of 27°C and 34°C, respectively. The results show that over 76% variation among different crops in SIF observations was explained by variation in vegetation biochemistry and structure. In addition, the changes of vegetation biochemistry and structure explained as much as 73% variation between the two days in far-red SIF, and 40% variation in red SIF. The remaining unexplained variation was mostly attributed to the variability in physiological status. We conclude that reflectance provides valuable information to account for biochemical and structural effects on SIF and to advance analysis of SIF observations. The combination of RTMs, reflectance and SIF opens new pathways to detect vegetation biochemical, structural and physiological changes.
关键词： Canopy structure,Radiative transfer models,Chlorophyll fluorescence,HyPlant,Airborne,Reflectance
更新于2025-09-09 09:28:46
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Comprehensive Remote Sensing || Solar Induced Chlorophyll Fluorescence: Origins, Relation to Photosynthesis and Retrieval
摘要： Photosynthesis has been key to Earth’s habitability, especially since the evolution of oxygenic photosynthesis with the accompanying rise in atmospheric O2 starting in the Proterozoic era, around 2.5 billion years ago. The conversion of light to chemical energy enables higher life forms and the presence of reduced carbon stocks and molecular O2 (accumulated products of photosynthesis) provided the fossil fuels for the initiation of our industrialized society. As a visible indicator of photosynthesis, fluorescence emanating from chlorophyll molecules attracted interest more than 100 years ago. In 1874, red fluorescence from a green living leaf was observed to be weaker than from a dilute chlorophyll solution (Müller, 1874), indicating an alternate fate for energy absorbed by chlorophyll in vivo. More quantitative studies of chlorophyll a fluorescence go back to observations by Hans Kautsky and A. Hirsch in 1931 at the Chemical Institute at the University of Heidelberg, Germany (Kautsky, 1931). They discovered the so-called Kautsky effect, a decrease in Chl fluorescence following illumination of dark-adapted leaves. Both studies already indicated an important aspect of chlorophyll fluorescence, namely, that its yield can vary. This effect is caused by variation in the balance of pathways that compete with fluorescence for quenching of the excited chlorophyll state. The porphyrin ring of the chlorophyll molecule is the center of light absorption and fluorescence. In a dilute chlorophyll solution, where fluorescence is the only route for de-excitation, the fluorescence lifetime (sF) is about 6 ns and the fluorescence yield (FF) approaches 1. In vivo, the excited chlorophyll state can be quenched by other processes, most notably photosynthesis itself but also quenching to heat; FF is lower (1%–5%) and the sF proportionally shorter. Fluorescence in itself is not a significant route for de-excitation of chlorophyll but changes in FF or sF can be used to study how absorbed energy is used. On the other hand, when FF is constant, fluorescence can provide information on the total amount of light absorbed, as the amount emitted will be proportional to the total amount of photosynthetically active radiation (PAR) that is absorbed by chlorophyll and associated pigments. Fig. 1 shows an example of a typical fluorescence spectrum as well as the absorbance spectrum by chlorophyll.
关键词： Fluorescence Yield,Solar Induced Chlorophyll Fluorescence,Chlorophyll,Photosynthesis,Remote Sensing
更新于2025-09-04 15:30:14
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A Method to Reconstruct the Solar-Induced Canopy Fluorescence Spectrum from Hyperspectral Measurements
摘要： A method for canopy Fluorescence Spectrum Reconstruction (FSR) is proposed in this study, which can be used to retrieve the solar-induced canopy fluorescence spectrum over the whole chlorophyll fluorescence emission region from 640–850 nm. Firstly, the radiance of the solar-induced chlorophyll fluorescence (Fs) at five absorption lines of the solar spectrum was retrieved by a Spectral Fitting Method (SFM). The Singular Vector Decomposition (SVD) technique was then used to extract three basis spectra from a training dataset simulated by the model SCOPE (Soil Canopy Observation, Photochemistry and Energy fluxes). Finally, these basis spectra were linearly combined to reconstruct the Fs spectrum, and the coefficients of them were determined by Weighted Linear Least Squares (WLLS) fitting with the five retrieved Fs values. Results for simulated datasets indicate that the FSR method could accurately reconstruct the Fs spectra from hyperspectral measurements acquired by instruments of high Spectral Resolution (SR) and Signal to Noise Ratio (SNR). The FSR method was also applied to an experimental dataset acquired in a diurnal experiment. The diurnal change of the reconstructed Fs spectra shows that the Fs radiance around noon was higher than that in the morning and afternoon, which is consistent with former studies. Finally, the potential and limitations of this method are discussed.
关键词： Fluorescence Spectrum Reconstruction (FSR),solar-induced chlorophyll fluorescence (Fs),Spectral Fitting Method (SFM),Fraunhofer Line Discriminator (FLD),hyperspectral remote sensing,Singular Vector Decomposition (SVD)
更新于2025-09-04 15:30:14
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Influence of Cosine Corrector and Uas Platform Dynamics on Airborne Spectral Irradiance Measurements
摘要： Measuring solar-induced chlorophyll fluorescence from small-sized Unmanned Aircraft Systems (UAS) can potentially fill the scaling gap between ground-based and airborne/space-borne observations. These measurements require well calibrated, high-spectral resolution spectroradiometers and precise measurements of vegetation radiance and incoming solar irradiance. Here we present a system equipped with a spectroradiometer with a split optical path that measures incoming irradiance through a cosine corrector/diffuser. The objectives of this study are to characterise cosine corrected solar irradiance measurements with regard to sensor homogeneity and possible offset from an ideal cosine response. We further suggest a methodology to calculate a corrected zenith angle that accounts for changing sensor orientation due to pitch, roll and heading of the UAS platform during flight. We found that the cosine corrector is sufficiently homogeneous, thus measurements are independent of UAS heading. The response follows the cosine law for zenith angles, however, the sensor significantly underestimated irradiance for zenith angles >10?, with overall cosine errors ranging from 0.991 to 1.229. Yet, typical in-flight platform pitch and roll angles produce a zenith angle offset of up to 6? in low wind conditions. Cosine sensor measurements corrected for the zenith angle offset and the cosine error resulted in a 1.7% change in irradiance.
关键词： irradiance cosine corrector,spectroradiometer,sun zenith angle,solar-induced chlorophyll fluorescence,unmanned aircraft system
更新于2025-09-04 15:30:14
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SENSITIVITY TO ENVIRONMENTAL STRESS OF PRATA,JAPIRA AND VITóRIA BANANA CULTIVARS PROVEN BY CHLOROPHYLL a FLUORESCENCE
摘要： This study aimed to evaluate the physiological responses to environmental stress during pre- and post-harvest of the following banana cultivars: Prata (AAB), Japira (AAAB) and Vitoria (AAAB). Analyses were carried out on young plants at vegetative stage (daughter-plant) and adult plants at reproductive stage (mother-plant). The experimental design was completely randomized. In the in vivo pre-harvest analysis were used seven replications, in a factorial scheme (3x2x2), three cultivars and two stages (vegetative and reproductive) and two collection periods (March and June). For the analysis of post-harvest quality were used five replications in a factorial design (3x2x5), corresponding to three cultivars, two development stages and five periods of post-harvest analysis, carried out every two days from stage 4 of fruit ripening. The chlorophyll a fluorescence emission kinetics showed low photochemical performance of the three cultivars in June, a period characterized by lower temperatures and water deficit. Prata was the cultivar with the lowest tolerance to abiotic physiological behavior changes, which also reflected in fruit quality, because there was a change in physical and physicochemical parameters. Japira and Vitoria cultivars showed similar physiological responses in the pre- and post-harvest periods, according to their phylogenetic proximity. The total performance index, i.e., the conservation of energy absorbed by PSII up to the reduction of the final PSI acceptors (PItotal) and the di-malonic aldehyde (MDA) content were significantly higher in Japira and Vitoria cultivars compared to Prata cultivar in the reproductive phase. There was no significant change in the potential quantum efficiency of PSII (FV / FM = jP0) among the three cultivars. It was concluded that Japira and Vitoria cultivars showed greater plasticity to tolerate or even adapt to abiotic variations keeping higher fruit yield. PItotal is the most sensitive parameter during the banana life cycle and important tool for distinguishing different cultivars yields.
关键词： Chlorophyll fluorescence,Musa spp.,post-harvest quality,lipid peroxidation,pigments
更新于2025-09-04 15:30:14