Chlorophyll Absorption Band Research Articles

Bi3+/Mn4+ co-doped Y2MgTiO6 dual-emitting phosphors for plant growth lighting and temperature sensor

Novel Bi3+/Mn4+ co-doped Y2MgTiO6 dual-emitting phosphors were synthesized using a high-temperature solid-phase method. The crystal structure and luminescence properties of phosphors were systematically investigated by experimental characterization and theoretical calculation. Under excitation at 375 nm, Y2MgTiO6:Bi3+, Mn4+ phosphors exhibit two emission bands located at 410 nm and 696 nm (blue and red), which can well be matched with the absorption bands of chlorophylls a, b and phytochrome. The Y2MgTiO6: Bi3+, Mn4+ luminescence remains at 66.2 % intensity at 423 K and quantum yield is 52.06 %. Optical temperature properties of Y2MgTiO6:Bi3+, Mn4+ were investigated using fluorescence intensity ratio (FIR) analysis and were found to reach a maximum relative sensitivity of 2.93 % K−1 at 498 K. The study suggests that this material could be a potential option for indoor plant culture and optical temperature sensing.

Enhancing the luminescence of Mn4+-doped double perovskite oxide Ca2LuNbO6 phosphor by utilizing A-site cationic fluoride as a flux

Supplement illumination is indispensable in the indoor plant cultivation domain. In this research work, double perovskite Ca2LuNbO6:Mn4+ phosphors were produced. A strategy of enhancing luminescence performance by utilizing A-site cationic fluoride as a flux was proposed. The structure and morphology of Ca2LuNbO6:Mn4+ phosphor was characterized. Under the excitation of 360 nm, the emission spectra of Ca2LuNbO6:Mn4+ phosphor cover from 600 nm to 750 nm peaking at 683 nm. It benefits the red section of chlorophyll absorption band and possesses the wavelengths of 680 nm and 700 nm demanded by photosystem I (PS I) and photosystem II (PS II) to realize Emerson enhancement effect. After adding CaF2 as flux, the emission intensity increases by 2.5 times. Due to its compatibility with the A-site cation of host, CaF2 agent not only lower the sintering temperature but also increase the crystallite size, which result in the enhancement of luminescence. The Dq/B and optical band gap of Ca2LuNbO6 host is 2.32 and 3.79 eV, respectively, which show that Mn4+ ions locate in the [NbO6] octahedra of strong crystal field and host has the suitable optical band gap for Mn4+ ions. With the help of CaF2, the thermal stability, activation energy ΔEa, internal quantum efficiency of Ca2LuNbO6:Mn4+ phosphors are promoted at 373 K from 64.8% to 70.7% of that at 273 K, from 0.33 to 0.36 eV, and from 9.1% to 23.5%. The luminescence lifetime of Ca2LuNbO6:Mn4+ is the order of a fraction of a millisecond. Finally, the as-prepared Ca2LuNb0.996O6:0.004Mn4+ phosphor was successfully fabricated through a 365 nm near ultraviolet (NUV) chip, which has the peak wavelengths of 683 nm and possesses 680 nm and 700 nm demanded by PS I and PS II. It is implied that Ca2LuNbO6:Mn4+ phosphor-converted light emitting diode has prospective market in the domain of supplement illumination of plant cultivation.

Mapping Plant Nitrogen Concentration and Aboveground Biomass of Potato Crops from Sentinel-2 Data Using Ensemble Learning Models

Excessive nitrogen (N) fertilization poses environmental risks at regional and global levels. Satellite remote sensing provides a novel approach for large-scale N monitoring. In this study, we evaluated the performance of different types of spectral bands and indices (SIs) coupled with ensemble learning models (ELMs) at retrieving the plant N concentration (PNC) and plant aboveground biomass (AGB) of potato from Sentinel-2 images. Cloud-free Sentinel-2 imagery was acquired during the tuber-formation to starch-accumulation stages from 2020 to 2021. Fourteen optimal SIs were selected using the successive projections algorithm (SPA) and principal component analysis (PCA). The PNC and AGB estimation models were then built using an ELMs. The results showed that the SIs based on chlorophyll absorption bands were strongly related to potato PNC and AGB. Also, the N-correlated bands were mainly concentrated in the red-edge (705 nm) and short-wave infrared (1610 and 2190 nm) regions. The ELMs successfully predicted PNC and AGB (R2PNC = 0.74; R2AGB = 0.82). Compared with the other five base models (k-nearest neighbor (KNN), partial least squares regression (PLSR), support vector regression (SVR), random forest (RF), and Gaussian process regression (GPR)), the ELMs provided higher PNC and AGB estimation accuracy and effectively reduced overfitting to training data. This study demonstrated that the promising solution of using SPA-PCA coupled with an ensemble learning model improves the estimation accuracy of potato PNC and AGB based on Sentinel-2 imagery data.

CAROTENOIDS AND CHLOROPHYLLS WHEN PRESENT TOGETHER: ANALYTICAL AND TECHNOLOGICAL FEATURES

Relevance.An analytical approach to choosing the direction of technological research has always been relevant, and taking into account the produc-tion of drugs using “green” extractants, the justification of technological parameters of extraction and its analytical support on models of already known, widely studied and used plant objects, for example, stinging nettle (Urtica dioica L.), can be considered as rational. The purpose of the study is an analytical study of carotenoids and chlorophylls in the co-presence of stinging nettle leaves and the rationale for the temperature regime for obtaining an oil extract from this plant, taking into account the co-presence of pigments in the extracts. Material and methods. The content of carotenoids and chlorophylls in raw materials and oil extracts was determined by spectrophotometry. Oil ex-tracts were obtained by fractional maceration at two temperature conditions: 25 °C and 50 °C. Results. The content of carotenoids and chlorophylls when jointly present in stinging nettle leaves was determined by spectrophotometry. When ob-taining six model oil extracts of stinging nettle leaves, the temperature regime was experimentally optimized at 50 °C; the optimization parameter was the quantitative content of carotenoids and chlorophylls. Conclusion. A detailed determination of the content of chlorophyll a, chlorophyll b, their sum and carotenoids in the presence of chlorophylls gives a detailed idea of the quantitative ratio of these types of pigments in the raw material and makes it possible to eliminate the overlap of absorption bands of carotenoids and chlorophylls. This approach made it possible to optimize the temperature conditions for obtaining the oil extract of nettle leaves. The applied analytical approach can be used to control the content of carotenoids and chlorophylls when present together to optimize the technological pa-rameters of oil extracts obtained from other types of medicinal plant raw materials.

Fluorescein-based vital dye for silicifying organisms

A method for the synthesis of a new amine-containing dye based on fluorescein (Flunet) was developed. The new dye exhibits pH-independent fluorescence in aqueous media and is able to penetrate living cells. Flunet can accumulate in the siliceous valve of diatom algae and cause cell death at a concentration of 0.5 μM, accompanied by chloroplast destruction. Flunet is nontoxic to yeasts and photosynthesizing dinoflagellates, but suppresses the growth of sponge primmorphs. Turning off the fluorescence of Flunet using a fluorescein shield protects diatom algae from death. Flunet, unlike other biosilica vital dyes, has emission in the red region (650–700 nm), which corresponds to the absorption band of chlorophyll. We suppose that once a significant amount of Flunet enters the siliceous valve of a diatom alga, it begins to convert blue light into green and red light, leading to the destruction of chloroplasts located very close (at the micrometer level) to the valve. Siliceous sponges can be suppressed in a similar way: light emitted by growing spicules destroys photosynthesizing sponge symbionts. Our findings open up a new way to influence silica-containing organisms by introducing different fluorescent dyes into the silica structures. This effect can be both positive (increased photosynthesis due to light tuning) and negative, leading to phototoxicity. Considering the main role of diatoms in biofouling of ships and other surfaces, the use of silica-penetrating dyes is a promising environmentally friendly way of antifouling protection.

Fully Integrated Ultrathin Solid Immersion Grating Microspectrometer for Handheld Visible and Near-Infrared Spectroscopic Applications.

Despite advances in microfabrication, compact spectrometers still face challenges in shrinking their size without sacrificing optical performance. Here, the solid immersion grating microspectrometer (SIG-µSPEC) for high spectral resolution in a broad operational wavelength range is reported. The spectroscopic module incorporates a silicon microslit, index-matched lens, plane mirrors, solid immersion grating (SIG), and a CMOS line sensor within a small form factor. The SIG facilitates high angular dispersion of light on a planar focal plane, resulting in an average spectral resolution of 5.8nm, with over 76% maximum sensitivity from 400 to 800nm. SIG-µSPEC measures the spectral reflectance of fruits at different ripening stages, clearly revealing changes in the chlorophyll absorption band. The measured spectrum is further utilized for the precise prediction of the soluble solid content (SSC) levels, achieving a high correlation (R2 = 0.91) and a ratio of prediction-to-deviation of 2.36. This compact microspectrometer holds the potential for precise and non-invasive spectral analysis across point-of-care fields.

LUMINESCENT COATINGS BASED ON PR-CONTAINING COMPLEX OXIDES FOR THE ELABORATION OF PHYTO-LEDS

Plants in greenhouses are grown under special lighting conditions, i.e. when partially or completely artificial lighting is used. For this purpose, various lamps are used - xenon, high or low pressure sodium, mercury, LED, etc. Recent studies have shown that LED lamps can achieve about 60 % more efficiency in greenhouse lighting than sodium lamps. The increased energy efficiency of LED lamps (phyto-lamps) is associated with the coincidence of their emission bands with the spectra of photosynthetic active radiation. The simplest phyto-lamps are devices consisting of several blue and red light LEDs (phyto-LEDs). A significant disadvantage of red LEDs those are based on the semiconductor structures is their cost, which is much higher than that of blue phyto-LEDs. One of the ways to reduce the price of red LEDs can be their elaboration on the basis of an InGaN semiconductor structure (chip) with a blue light emission, with a deposited layer of an inorganic phosphor. Phosphors with a red emission can be created on the basis of oxide materials with ions of transition or rare earth metals, such as Pr3+. The advantage of praseodymium over transition element ions is that the main absorption bands of Pr3+ ions in the visible region located in the range of 430–490 nm, namely in the emission region of blue LEDs. The position of these bands weakly depends on the type of crystalline or glass matrix. In this work, luminescent coatings based on KBi(MoO4)2 and K2Bi(PO4)(MoO4) crystals doped with Pr3+ ions are considered. The coating on the LED was carried out using a polymer - cyanoacrylate glue. It has been found that the polymer used weakly absorbs LED radiation and does not exhibit significant luminescence in the visible region upon excitation at 446 nm. For a coating based on K2Bi0.99Pr0.01(PO4)(MoO4), it was shown that, in terms of the position of the oxide luminescence bands, it agrees well with the red absorption band of chlorophyll b and with weak absorption bands of chlorophyll in the range of 590–620 nm. However, the efficiency of blue into red light converting for this coating is rather low. Better results can be achieved with KBi0.9Pr0.1(MoO4)2, which has a better correlation with chlorophyll’s absorption bands, as well as a higher blue-to-red conversion efficiency. In our opinion, by varying the content of praseodymium in KBi1-xPrx(MoO4)2 and optimizing the deposition method, it is possible to increase the efficiency of such luminescent coatings for the development of phyto-LEDs.

Proton motive force in plant photosynthesis dominated by ΔpH in both low and high light.

The proton motive force (pmf) across the thylakoid membrane couples photosynthetic electron transport and ATP synthesis. In recent years, the electrochromic carotenoid and chlorophyll absorption band shift (ECS), peaking ∼515 nm, has become a widely used probe to measure pmf in leaves. However, the use of this technique to calculate the parsing of the pmf between the proton gradient (ΔpH) and electric potential (Δψ) components remains controversial. Interpretation of the ECS signal is complicated by overlapping absorption changes associated with violaxanthin de-epoxidation to zeaxanthin (ΔA505) and energy-dependent nonphotochemical quenching (qE; ΔA535). In this study, we used Arabidopsis (Arabidopsis thaliana) plants with altered xanthophyll cycle activity and photosystem II subunit S (PsbS) content to disentangle these overlapping contributions. In plants where overlap among ΔA505, ΔA535, and ECS is diminished, such as npq4 (lacking ΔA535) and npq1npq4 (also lacking ΔA505), the parsing method implies the Δψ contribution is virtually absent and pmf is solely composed of ΔpH. Conversely, in plants where ΔA535 and ECS overlap is enhanced, such as L17 (a PsbS overexpressor) and npq1 (where ΔA535 is blue-shifted to 525 nm) the parsing method implies a dominant contribution of Δψ to the total pmf. These results demonstrate the vast majority of the pmf attributed by the ECS parsing method to Δψ is caused by ΔA505 and ΔA535 overlap, confirming pmf is dominated by ΔpH following the first 60 s of continuous illumination under both low and high light conditions. Further implications of these findings for the regulation of photosynthesis are discussed.

Synthesis and luminescence properties of double perovskite Bi3+/Mn4+ co-doped Ca2GdTaO6 phosphor

Bi3+-doped, Mn4+-doped, and Bi3+/Mn4+ co-doped oxide phosphors Ca2GdTaO6 (CGT) are prepared via the solid-state reaction method. The phase purity and morphology of CGT: Bi3+, Mn4+ phosphors are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The band structure and density of state for CGT are calculated based on density functional theory (DFT). The bandgap of the CGT host is 3.72 eV. The photoluminescence (PL) and photoluminescence excitation (PLE) spectra of CGT: Bi3+ and CGT: Mn4+ is investigated in detail. The overlap between the emission spectra of Bi3+ and the excitation of Mn4+ proves energy transfer from Bi3+ to Mn4+. The corresponding mechanism of the Bi3+→Mn4+ energy transfer process is investigated in detail based on the decay time and PL spectra. Energy transfer efficiency is also calculated. Upon excitation at 320 nm, Bi3+/Mn4+ co-doped CGT phosphors show dual emission attributed to the blue-violet emission (429 nm) of 3P1→1S0 transition of Bi3+ and red emission (679 nm) of 2Eg→4A2g of Mn4+. The intensity of the blue-violet and red emission peaks can be easily adjusted by controlling the concentration of Bi3+ and Mn4+ in the CGT host. The emission band is well-matched with the absorption bands of chlorophylls a and phytochrome PR under the near-ultraviolet to blue excitation, suggesting that the phosphors have great potential applications in light-emitting diodes (LEDs) to modulate plant growth.

A TDDFT investigation of the Photosystem II reaction center: Insights into the precursors to charge separation

Photosystem II (PS II) captures solar energy and directs charge separation (CS) across the thylakoid membrane during photosynthesis. The highly oxidizing, charge-separated state generated within its reaction center (RC) drives water oxidation. Spectroscopic studies on PS II RCs are difficult to interpret due to large spectral congestion, necessitating modeling to elucidate key spectral features. Herein, we present results from time-dependent density functional theory (TDDFT) calculations on the largest PS II RC model reported to date. This model explicitly includes six RC chromophores and both the chlorin phytol chains and the amino acid residues <6 Å from the pigments' porphyrin ring centers. Comparing our wild-type model results with calculations on mutant D1-His-198-Ala and D2-His-197-Ala RCs, our simulated absorption-difference spectra reproduce experimentally observed shifts in known chlorophyll absorption bands, demonstrating the predictive capabilities of this model. We find that inclusion of both nearby residues and phytol chains is necessary to reproduce this behavior. Our calculations provide a unique opportunity to observe the molecular orbitals that contribute to the excited states that are precursors to CS. Strikingly, we observe two high oscillator strength, low-lying states, in which molecular orbitals are delocalized over ChlD1 and PheD1 as well as one weaker oscillator strength state with molecular orbitals delocalized over the P chlorophylls. Both these configurations are a match for previously identified exciton-charge transfer states (ChlD1+PheD1-)* and (PD2+PD1-)*. Our results demonstrate the power of TDDFT as a tool, for studies of natural photosynthesis, or indeed future studies of artificial photosynthetic complexes.

Dependence of Chlorophyll Content in Leaves from The Light Regime, Electromagnetic Fields and Plant Species

The regularity of the distribution of chlorophylls content in a series of 30 cultivated plants and 75 steppe grasses was studied. The increased content of chlorophyll and magnesium in vegetables and grains compared with greens and steppe grasses is associated with more complex genetics of metabolism, which has stages of flowering and fruiting. The chlorophyll content increases with the use of LED phytoirradiators with an emission band coinciding with the first absorption band of chlorophyll. Industrial electromagnetic fields can affect the biosynthesis of pigments in deciduous trees, but cultivated herbaceous plants are not sensitive to them.

Potential of hyperspectral data and machine learning algorithms to estimate the forage carbon-nitrogen ratio in an alpine grassland ecosystem of the Tibetan Plateau

The carbon-nitrogen (C:N) ratio plays a crucial role in regulation of the nutrient utilization efficiency and growth rate of plants. However, challenges are faced when hyperspectral data are directly used to estimate the C:N ratio due to the lack of corresponding sensitive feature bands. This study aims to explore the feasibility of using important bands (IBs) determined for the C:N ratio and known absorption bands (KBs) of protein, chlorophyll, N, and carbon-containing compounds from hyperspectral measurements to estimate the forage C:N ratio. Random forest (RF) and support vector machine (SVM) algorithms are employed to establish a model for the estimation of the forage C:N ratio. The results show that the KBs exhibit good performance in estimating the forage C:N ratio (V-R2 of 0.70–0.80, with a mean of 0.77), and the IBs derived from the red and red-edge regions significantly contribute to the forage C:N ratio estimation, with V-R2 of 0.77–0.80. This study also demonstrates that the models based on combined bands (CBs) (the combination of KBs and IBs) slightly improve the accuracy of the forage C:N ratio estimation. Moreover, further optimization of the CBs produces satisfactory estimation of the forage C:N ratio (V-R2 = 0.82, V-RMSE = 5.53), explaining 85–92% of the variation in the forage C:N ratio at the different growth stages (May to November). Overall, the direct estimation of the forage C:N ratio in alpine grassland using hyperspectral feature bands is promising.

Estimating Net Photosynthesis of Biological Soil Crusts in the Atacama Using Hyperspectral Remote Sensing

Biological soil crusts (BSC) encompassing green algae, cyanobacteria, lichens, bryophytes, heterotrophic bacteria and microfungi are keystone species in arid environments because of their role in nitrogen- and carbon-fixation, weathering and soil stabilization, all depending on the photosynthesis of the BSC. Despite their importance, little is known about the BSCs of the Atacama Desert, although especially crustose chlorolichens account for a large proportion of biomass in the arid coastal zone, where photosynthesis is mainly limited due to low water availability. Here, we present the first hyperspectral reflectance data for the most wide-spread BSC species of the southern Atacama Desert. Combining laboratory and field measurements, we establish transfer functions that allow us to estimate net photosynthesis rates for the most common BSC species. We found that spectral differences among species are high, and differences between the background soil and the BSC at inactive stages are low. Additionally, we found that the water absorption feature at 1420 nm is a more robust indicator for photosynthetic activity than the chlorophyll absorption bands. Therefore, we conclude that common vegetation indices must be taken with care to analyze the photosynthesis of BSC with multispectral data.

Fast nondestructive identification of steamed green tea powder adulterations in matcha by visible spectroscopy combined with chemometrics

ABSTRACTCompared with green tea powder, whether enzyme-deactivated by steam or pan-fire, matcha is rich in nutrients, but is more expensive. Using steamed green tea powder to adulterate matcha often occurs and this study provided an effective method to identify steamed green tea powder adulterations in matcha rapidly and nondestructively with the combination of visible spectroscopy and chemometrics. Thirty pure matcha samples, 30 100% steamed green tea powder samples and 120 adulterated samples with steamed green tea powder’s concentration from 20% to 80% (w/w) were prepared and their spectra of 500–700 nm were acquired and applied for the qualitative classification and quantitative prediction. The principal component analysis–linear discriminant analysis model and the soft independent modeling of class analogy model in the qualitative classification as well as the partial least squares model in the quantitative analysis performed well with the accuracy of 100% and R2 of 0.9815 in their corresponding prediction sets. Because of the covering step during its longer growth period, matcha contained more contents of chlorophyll b than steamed green tea powder, which made the absorption band of chlorophyll b at 645 nm become the major contributing band both in discriminant and quantification models.

Spectral analysis of amazon canopy phenology during the dry season using a tower hyperspectral camera and modis observations

The association between spectral reflectance and canopy processes remains challenging for quantifying large-scale canopy phenological cycles in tropical forests. In this study, we used a tower-mounted hyperspectral camera in an eastern Amazon forest to assess how canopy spectral signals of three species are linked with phenological processes in the 2012 dry season. We explored different approaches to disentangle the spectral components of canopy phenology processes and analyze their variations over time using 17 images acquired by the camera. The methods included linear spectral mixture analysis (SMA); principal component analysis (PCA); continuum removal (CR); and first-order derivative analysis. In addition, three vegetation indices potentially sensitive to leaf flushing, leaf loss and leaf area index (LAI) were calculated: the Enhanced Vegetation Index (EVI), Normalized Difference Vegetation Index (NDVI) and the entitled Green-Red Normalized Difference (GRND) index. We inspected also the consistency of the camera observations using Moderate Resolution Imaging Spectroradiometer (MODIS) and available phenological data on new leaf production and LAI of young, mature and old leaves simulated by a leaf demography-ontogeny model. The results showed a diversity of phenological responses during the 2012 dry season with related changes in canopy structure and greenness values. Because of the differences in timing and intensity of leaf flushing and leaf shedding, Erisma uncinatum, Manilkara huberi and Chamaecrista xinguensis presented different green vegetation (GV) and non-photosynthetic vegetation (NPV) SMA fractions; distinct PCA scores; changes in depth, width and area of the 681-nm chlorophyll absorption band; and variations over time in the EVI, GRND and NDVI. At the end of dry season, GV increased for Erisma uncinatum, while NPV increased for Chamaecrista xinguensis. For Manilkara huberi, the NPV first increased in the beginning of August and then decreased toward September with new foliage. Variations in red-edge position were not statistically significant between the species and across dates at the 95% confidence level. The camera data were affected by view-illumination effects, which reduced the SMA shade fraction over time. When MODIS data were corrected for these effects using the Multi-Angle Implementation of Atmospheric Correction Algorithm (MAIAC), we observed an EVI increase toward September that closely tracked the modeled LAI of mature leaves (3–5months). Compared to the EVI, the GRND was a better indicator of leaf flushing because the modeled production of new leaves peaked in August and then declined in September following the GRND closely. While the EVI was more related to changes in mature leaf area, the GRND was more associated with new leaf flushing.

Seasonal characterization and discrimination of savannah physiognomies in Brazil using hyperspectral metrics from Hyperion/EO-1

ABSTRACTThe seasonal characterization and discrimination of savannahs in Brazil are still challenging due to the high spatial variability of the vegetation cover and the spectral similarity between some physiognomies. As a preparatory study for future hyperspectral missions that will operate with large swath width and better signal-to-noise ratio than the current orbital sensors, we evaluated six Hyperion images acquired over the Estação Ecológica de Águas Emendadas, a protected area in central Brazil. We studied the seasonal variations in spectral response of the savannah physiognomies and tested their discrimination in the rainy and dry seasons using distinct sets of hyperspectral metrics. Floristic and structural attributes were inventoried in the field. We considered three sets of metrics in the data analysis: the reflectance of 146 Hyperion bands, 22 narrowband vegetation indices (VIs), and 24 absorption band parameters. The VIs were selected to represent vegetation structure, biochemistry, and physiology. The depth, area, width, and asymmetry of the major absorption bands centred at 680 nm (chlorophyll), 980, and 1200 nm (leaf water) and 1700, 2100, and 2300 nm (lignin-cellulose) were calculated on a per-pixel basis using the continuum removal method. Using feature selection and multiple discriminant analysis (MDA), we tested the discriminatory capability of these metrics and of their combined use for vegetation discrimination in the rainy and dry seasons. The results showed that the spectral modifications with seasonality were stronger with the savannah woodland-grassland gradient represented by decreasing tree height, basal area, tree density and biomass and by increasing canopy openness. We observed a reflectance increase in the red, red edge, and shortwave (SWIR) intervals towards the dry season. In the near-infrared, the reflectance differences between the physiognomies were smaller in the dry season than in the rainy season. From the 22 VIs, the visible atmospherically resistant index (VARI), visible green index (VIg), and normalized difference infrared index (NDII) were the most sensitive indices to water stress and vegetation cover, presenting the largest rates of changes between the rainy (March) and dry (August) seasons in shrub and grassland areas. Absorption band parameters associated with the lignin-cellulose spectral features in the SWIR increased towards the dry season with great amounts of non-photosynthetic vegetation (NPV) in the herbaceous stratum. The opposite was observed for the 680 nm chlorophyll absorption band and the 980 and 1200 nm leaf water features. In general, the number of selected metrics necessary for vegetation discrimination was lower in the dry season than in the rainy season. The best MDA-classification accuracy was obtained in the dry season using nine VIs (79.5%). The combination of different hyperspectral metrics increased the classification accuracy to 81.4% in the rainy season and to 84.2% in the dry season. This combination added a gain higher than 10% for the classification of shrub savannah, open woodland savannah and wooded savannah.

Influencia del ángulo de observación en la estimación del índice de área foliar (LAI) mediante imágenes PROBA/CHRIS

&lt;p&gt;The estimation of biophysical variables, such as the Leaf Area Index (LAI), using remote sensing techniques, is still the subject of numerous studies, since these variables allow obtaining valuable information on the vegetation status. In this work, we estimate LAI from multiangular PROBA/CHRIS images, by analyzing the reflectance measured in its 5 observation angles, for the bands centered in 665 and 705 nm. These wavelengths correspond to the chlorophyll absorption band and the Red-Edge region, respectively. The Normalized Difference Index (NDI) calculated from this wavelengths, shows good correlation with LAI and allows its remote sensing estimation and its applicability to the recently launched ESA Sentinel 2, thanks to its new bands in the Red-Edge. This research analyzed the influence on the acquisition geometry in the NDI, calibrating the relationship between this index and the LAI for each of the five observation angles in the PROBA / CHRIS images. As a result, we have obtained a relationship capable of providing LAI from the viewing angle and the NDI index.&lt;/p&gt;

Narrowband shortwave minima in spectra of backscattered light from the sea obtained from ocean color scanners as a remote indication of algal blooms

Summary We propose a new approach to indication of algal blooms. It stems from analysis of the multispectral satellite reflectance R rs of areas where blooms were documented during recent decades. We found that spectra of algal blooms exhibit minima at wavelengths of channels of Moderate Resolution Imaging Spectroradiometer (MODIS) λ = 443 and λ = 488 nm (Baltic, Black, and Caspian seas), λ = 443 nm (Southwest Tropical Pacific (SWTP)), and λ = 443 nm and λ = 469 nm (Patagonian Continental Shelf (PCS)), attributable to absorption bands of chlorophyll a and accessory pigments. We quantified the minima using indices D1 = R rs (443) − R rs (412) and D2 = R rs (488) − R rs (469) and proved their diagnostic potential by comparing their distributions to that of R rs (555). Linear dependence of D1 upon chlorophyll a was found from MODIS data for the bloom of Nodularia spumigena . Time dependences of D1 and D2 point to the latter as a probable remote forerunner of cyanobacterial blooms. In the PCS, D1 and D2 proved to be too simplistic owing to diversity of spectral shapes at λ

Low-temperature (77K) phosphorescence of triplet chlorophyll in isolated reaction centers of photosystem II.

Phosphorescence characterized by the main emission band at 952±1nm (1.30eV), the lifetime of 1.5±0.1ms and the quantum yield nearly equal to that for monomeric chlorophyll a in aqueous detergent dispersions, has been detected in isolated reaction centers (RCs) of spinach photosystem II at 77K. The excitation spectrum shows maxima corresponding to absorption bands of chlorophyll a, pheophytin a, and β-carotene. The phosphorescence intensity strongly depends upon the redox state of RCs. The data suggest that the phosphorescence signal originates from the chlorophyll triplet state populated via charge recombination in the radical pair [Formula: see text].

A novel reflectance-based model for evaluating chlorophyll concentrations of fresh and water-stressed leaves

Abstract. Water deficits can cause chlorophyll degradation which decreases the total concentration of chlorophyll a and b (Chls). Few studies have investigated the effectiveness of spectral indices under water-stressed conditions. Chlorophyll meters have been extensively used for a wide variety of leaf chlorophyll and nitrogen estimations. Since a chlorophyll meter works by sensing leaves absorptance and transmittance, the reading of chlorophyll concentration will be affected by changes in transmittance as if there were a water deficit in the leaves. The overall objective of this paper was to develop a novel and reliable reflectance-based model for estimating Chls of fresh and water-stressed leaves using the reflectance at the absorption bands of chlorophyll a and b and the red edge spectrum. Three independent experiments were designed to collect data from three leaf sample sets for the construction and validation of Chls estimation models. First, a reflectance experiment was conducted to collect foliar Chls and reflectance of leaves with varying water stress using the ASD FieldSpec spectroradiometer. Second, a chlorophyll meter (SPAD-502) experiment was carried out to collect foliar Chls and meter readings. These two data sets were separately used for developing reflectance-based or absorptance-based Chls estimation models using linear and nonlinear regression analysis. Suitable models were suggested mainly based on the coefficient of determination (R2). Finally, an experiment was conducted to collect the third data set for the validation of Chls models using the root mean squared error (RMSE) and the mean absolute error (MAE). In all of the experiments, the observations (real values) of the foliar Chls were extracted from acetone solution and determined by using a Hitachi U-2000 spectrophotometer. The spectral indices in the form of reflectance ratio/difference/slope derived from the Chl b absorption bands (ρ645 and ρ455) provided Chls estimates with RMSE around 0.40–0.55 mg g−1 for both fresh and water-stressed samples. We improved Chls prediction accuracy by incorporating the reflectance at red edge position (ρREP) in regression models. An effective chlorophyll indicator with the form of (ρ645–ρ455)/ρREP proved to be the most accurate and stable predictor for foliar Chls concentration. This model was derived with an R2 of 0.90 (P &lt; 0.01) from the training samples and evaluated with RMSE 0.35 and 0.38 mg g−1 for the validation samples of fresh and water-stressed leaves, respectively. The average prediction error was within 14% of the mean absolute error.