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Plant species diversity is key to ecosystem functioning, but in recent decades anthropogenic activities have prompted an alarming decline in this community trait. Thus, developing strategies to understand diversity dynamics based on affordable and efficient remote sensing monitoring is essential, as well as examining the relevance of spatial scale and vegetation structural complexity to these dynamics. Here, we used two mathematical approaches to assess the relationship between tropical woody species diversity and spectral diversity in a human-modified landscape in two vegetation types differing in their degree of complexity. Vegetation complexity was measured through the fraction of species that concentrate different proportions of the cumulative importance value index. Species diversity was assessed using Hill numbers at three spatial scales, and metrics of spectral heterogeneity, vegetation indices, as well as raw data from Landsat 9 and Sentinel-2 sensors were calculated and analysed through general linear models (GLM) and Random Forest. Vegetation complexity emerged as an important variable in modelling species from remote sensing metrics, indicating the need to model species diversity by vegetation type rather than region. Hill numbers showed different relationships with remotely sensed metrics, in consistency with the scale-dependency of ecological processes on species diversity. Contrary to multiple previous reports, in our study, GLMs produced the best fits between Hill numbers of all orders and remotely sensed metrics. If we are to meet the need of conducting efficient and speedy woody species diversity monitoring globally, we propose modelling this diversity from remotely-sensed variables as an attractive strategy, so long as the intrinsic properties of each vegetation type are acknowledged to avoid under- or overestimation biases. [ABSTRACT FROM AUTHOR]

Heterogeneity in the fluorescence of carbon dots (CDs) has been hard to figure out so far. This could potentially be related to structural factors, size or intermediate fluorophores, especially when employing the bottom‐up synthesis. Herein, we unveil the origin of fluorescence and spectral heterogeneity of CDs using a simple dynamic method. This work reports the room light‐excited green fluorescence and dual‐emissive N‐doped CDs synthesized using a hydrothermal method. Studies were carried out considering the factors of fluorescence phenomena, such as excitation‐independent emission, fluorescent impurities, aggregation and solvation dynamics. The new steady‐state, Excitation‐resolved area‐normalized emission spectroscopy (ERANES) and ensemble measurements, including time‐resolved studies reveal that a heterogeneous environment exists in the ground state. Eventually, the results show the existence of core, edge and surface states in the CDs. Additionally, the fluorescence characteristics depend on the structural functionalization that occurs in both the intrinsic and extrinsic states of the CDs and it is proven that this does not violate the Kasha‐Vavilov rule. Although a highly purified material could still exhibit heterogeneity due to the ensemble emissive states and structural variations. Our results provide insights into the enduring debates about fluorescence and a deeper understanding of the structure‐ property relationship of CDs. [ABSTRACT FROM AUTHOR]

At present, the accuracy of remote sensing estimation models of plant alpha diversity is generally low, and high-precision estimation models in deciduous broadleaved forest (DBF), deciduous coniferous forest (DCF) and evergreen coniferous forest (ECF) are still lacking. The main purpose of this study is to construct high-precision remote sensing models for plant alpha diversity in multiple ecosystems at global scale. Normalized Difference Vegetation Index (NDVI) were derived from Sentinel-2 data. NDVI and NDVI based spectral diversity/heterogeneity indices were selected as predictive variables, and alpha diversity indices were selected as response variables. Simple linear regression (SLR), partial linear regression (PLSR), and random forest (RF) models were used to evaluate the predictive ability of the predictive variables against the response variables under six ecosystems (evergreen broadleaved forest (EBF), DBF, ECF, DCF, shrub, and grassland), and to compare the estimated robustness of various spectral diversity indices. In terms of prediction accuracy, the SLR models were the worst, and the PLSR model were average. RF performed best, outperforming most current models. Especially in DBF, ECF, shrub and grassland, the determination coefficient R2 of RF models can be as high as 0.9. In terms of the prediction of α-diversity, the prediction effect of species richness was better than that of Shannon index, Simpson index and Pielou index. The higher the vegetation complexity, the more accurate the assessment of vegetation α-diversity tends to be, especially in DBF, shrub and grassland. According to the importance of predictive variables and model stability evaluation results, NDVI, standard deviation of NDVI (SD), and NDVI derived Shannon’s diversity index (Sha), Cumulative Residual Entropy (CRE), Pielou’s evenness index (Pie), Hill’s numbers (Hill), Berger-Parker’s diversity index (Ber), Parametric Rao’s index of quadratic entropy (paRao) are all powerful indicators for predicting plant alpha diversity. Among them, the prediction performance of NDVI and SD is better. This study is not only an exploration of the practicability of R package “rasterdiv”, but also an attempt to construct high-precision remote sensing estimation models of plant alpha diversity at global scale.

To identify areas of high biodiversity and prioritize conservation efforts, it is crucial to understand the drivers of species richness patterns and their scale dependence. While classified land cover products are commonly used to explain bird species richness, recent studies suggest that unclassified remote-sensed images can provide equally good or better results. In our study, we aimed to investigate whether unclassified multispectral data from Landsat 8 can replace image classification for bird diversity modeling. Moreover, we also tested the Spectral Variability Hypothesis.Using the Atlas of Breeding Birds in the Czech Republic 2014-2017, we modeled species richness at two spatial resolutions of approx. 131 km2 (large squares) and 8 km2 (small squares). As predictors of the richness, we assessed 1) classified land cover data (Corine Land Cover 2018 database), 2) spectral heterogeneity (computed in three ways) and landscape composition derived from unclassified remote-sensed reflectance and vegetation indices. Furthermore, we integrated information about the landscape types (expressed by the most prevalent land cover class) into models based on unclassified remote-sensed data to investigate whether the landscape type plays a role in explaining bird species richness.We found that unclassified remote-sensed data, particularly spectral heterogeneity metrics, were better predictors of bird species richness than classified land cover data. The best results were achieved by models that included interactions between the unclassified data and landscape types, indicating that relationships between bird diversity and spectral heterogeneity vary across landscape types.Our findings demonstrate that spectral heterogeneity derived from unclassified multispectral data is effective for assessing bird diversity across the Czech Republic. When explaining bird species richness, it is important to account for the type of landscape and carefully consider the significance of the chosen spatial scale.

Questions: Can we map complex habitat mosaics from remote‐sensing data? In doing this, are measures of spectral heterogeneity useful to improve image classification performance? Which measures are the most important? How can multitemporal data be integrated in a robust framework? Location: Classical Karst (NE Italy). Methods: First, a habitat map was produced from field surveys. Then, a collection of 12 monthly Sentinel‐2 images was retrieved. Vegetation and spectral heterogeneity (SH) indices were computed and aggregated in four combinations: (1) monthly layers of vegetation and SH indices; (2) seasonal layers of vegetation and SH indices; (3) yearly layers of SH indices computed across the months; and (4) yearly layers of SH indices computed across the seasons. For each combination, a Random Forest classification was performed, first with the complete set of input layers and then with a subset obtained by recursive feature elimination. Training and validation points were independently extracted from field data. Results: The maximum overall accuracy (0.72) was achieved by using seasonally aggregated vegetation and SH indices, after the number of vegetation types was reduced by aggregation from 26 to 11. The use of SH measures significantly increased the overall accuracy of the classification. The spectral β‐diversity was the most important variable in most cases, while the spectral α‐diversity and Rao's Q had a low relative importance, possibly because some habitat patches were small compared to the window used to compute the indices. Conclusions: The results are promising and suggest that image classification frameworks could benefit from the inclusion of SH measures, rarely included before. Habitat mapping in complex landscapes can thus be improved in a cost‐ and time‐effective way, suitable for monitoring applications. [ABSTRACT FROM AUTHOR]

• Satellite high-precision estimation for plant diversity is extremely needed. • Simple linear regression models were the worst. • Partial linear regression model was moderate. • Random forest model performed best. • NDVI and its standard deviation are the best predictors for plant alpha diversity. At present, the accuracy of remote sensing estimation models of plant alpha diversity is generally low, and high-precision estimation models in deciduous broadleaved forest (DBF), deciduous coniferous forest (DCF) and evergreen coniferous forest (ECF) are still lacking. The main purpose of this study is to construct high-precision remote sensing models for plant alpha diversity in multiple ecosystems at global scale. Normalized Difference Vegetation Index (NDVI) were derived from Sentinel-2 data. NDVI and NDVI based spectral diversity/heterogeneity indices were selected as predictive variables, and alpha diversity indices were selected as response variables. Simple linear regression (SLR), partial linear regression (PLSR), and random forest (RF) models were used to evaluate the predictive ability of the predictive variables against the response variables under six ecosystems (evergreen broadleaved forest (EBF), DBF, ECF, DCF, shrub, and grassland), and to compare the estimated robustness of various spectral diversity indices. In terms of prediction accuracy, the SLR models were the worst, and the PLSR model were average. RF performed best, outperforming most current models. Especially in DBF, ECF, shrub and grassland, the determination coefficient R2 of RF models can be as high as 0.9. In terms of the prediction of α-diversity, the prediction effect of species richness was better than that of Shannon index, Simpson index and Pielou index. The higher the vegetation complexity, the more accurate the assessment of vegetation α-diversity tends to be, especially in DBF, shrub and grassland. According to the importance of predictive variables and model stability evaluation results, NDVI, standard deviation of NDVI (SD), and NDVI derived Shannon's diversity index (Sha), Cumulative Residual Entropy (CRE), Pielou's evenness index (Pie), Hill's numbers (Hill), Berger-Parker's diversity index (Ber), Parametric Rao's index of quadratic entropy (paRao) are all powerful indicators for predicting plant alpha diversity. Among them, the prediction performance of NDVI and SD is better. This study is not only an exploration of the practicability of R package "rasterdiv", but also an attempt to construct high-precision remote sensing estimation models of plant alpha diversity at global scale. [ABSTRACT FROM AUTHOR]

Twenty years ago, the Spectral Variation Hypothesis (SVH) was formulated as a means to link between different aspects of biodiversity and spatial patterns of spectral data (e.g. reflectance) measured from optical remote sensing. This hypothesis initially assumed a positive correlation between spatial variations computed from raster data and spatial variations in the environment, which would in turn correlate with species richness: following SVH, areas characterized by high spectral heterogeneity (SH) should be related to a higher number of available ecological niches, more likely to host a higher number of species when combined. The past decade has witnessed major evolution and progress both in terms of remotely sensed data available, techniques to analyze them, and ecological questions to be addressed. SVH has been tested in many contexts with a variety of remote sensing data, and this recent corpus highlighted potentials and pitfalls. The aim of this paper is to review and discuss recent methodological developments based on SVH, leading progress in ecological knowledge as well as conceptual uncertainties and limitations for the application of SVH to estimate different dimensions of biodiversity. In particular, we systematically review more than 130 publications and provide an overview of ecosystems, the different remote sensing data characteristics (i.e., spatial, spectral and temporal resolution), metrics, tools, and applications for which the SVH was tested and the strength of the association between SH and biodiversity metrics reported by each study. In conclusion, this paper serves as a guideline for researchers navigating the complexities of applying the SVH, offering insights into the current state of knowledge and future research possibilities in the field of biodiversity estimation by remote sensing data. • We reviewed and discussed recent methodological developments based on SVH. • Ecosystems, indices, data and approaches have been deeply revised. • The uncertainties related to the SVH have been thoroughly analyzed. • Future aspects and new prospective have been highlighted. [ABSTRACT FROM AUTHOR]

In high-resolution maritime surveillance radars, sea clutter exhibits highly spatial heterogeneity due to modulation of long waves with wavelengths longer than the width of one range cell. Compound-Gaussian model (CGM) fails to characterize the heterogeneous high-resolution sea clutter in both amplitude distribution and Doppler spectrum. In this article, a bi-phase compound-Gaussian mixture model (BP-CGMM) is proposed to characterize the heterogeneous sea clutter. In the BP-CGMM, spatial resolution cells are grouped into two disjoint sets, and the sea clutter in each set is represented by one CGM with inverse Gamma-distributed texture. The spectral heterogeneity indicates that sea clutter vectors at spatially adjacent resolution cells in one set share the same speckle covariance matrix, while that at two adjacent spatial cells separated in the two sets often have different speckle covariance matrices. The BP-CGMM is validated by a mass of measured high-resolution sea clutter data. Moreover, under the BP-CGMM, a detection method based on batch test is given to detect sea-surface small targets, which is composed of scene segmentation, by the aid of Bayesian threshold and morphological filtering, and adaptive generalized likelihood ratio test linear-threshold detector (GLRT-LTD) separately in each set. The detection method is verified by measured data with small targets under test. The experimental results show that it attains better detection performance than the adaptive GLRT-LTD under the CGM of sea clutter.

Plant diversity safeguards wetland ecosystem functions, stability, and resilience, but is threatened by habitat loss and degradation. Remote sensing could support the cost-effective management of biodiversity by providing consistent and frequent data at large scales. While identifying individual species from remote sensing datasets with low spatial and spectral resolution is challenging, studies can focus on factors known to correlate with or promote diversity. We tested the predictive potential of such factors — maximum annual greenness as an indicator of productivity, texture (i.e., spatial arrangement of grey tones) as a proxy for habitat heterogeneity, and spatial autocorrelation — across a dataset of 1115 wetlands in the conterminous United States surveyed by the EPA's National Wetland Condition Assessment. We used multivariate linear regressions to test whether spectral and spatial metrics derived from two open-source datasets — NASA's Landsat 5 TM and 7 ETM+ (30 m, 16-day revisit) and USDA's National Agriculture Inventory Program (1 m, biennial) — can predict wetland plant diversity and richness. Individual texture metrics showed different sensitivity to vegetation evenness, growth form, and spatial distribution and could together predict 35–36% of site variation in richness and diversity. This highlights the impact of habitat heterogeneity on species diversity and spectral variability. While maximum annual greenness and texture metrics had similar predictive capacity, their interactions and combined effects improved the fit of linear models by 11–14%, demonstrating their complementarity. Best results were achieved when including distance-based Moran's Eigenvector Maps (dbMEMs) describing spatial relations among sites at multiple scales and reflecting the role of spatially structured factors (e.g., climate, topography, dispersal) on diversity. Together greenness, texture, and dbMEMs could predict 59% of plant richness and 50% of plant diversity across the entire dataset and up to 71% of the richness of least disturbed sites. These results show the potential of open-source remote sensing datasets to monitor biodiversity resources at a large scale and prioritize the protection and field monitoring of wetlands. [ABSTRACT FROM AUTHOR]

To identify areas of high biodiversity and prioritize conservation efforts, it is crucial to understand the drivers of species richness patterns and their scale dependence. While classified land cover products are commonly used to explain bird species richness, recent studies suggest that unclassified remote-sensed images can provide equally good or better results. In our study, we aimed to investigate whether unclassified multispectral data from Landsat 8 can replace image classification for bird diversity modeling. Moreover, we also tested the Spectral Variability Hypothesis. Using the Atlas of Breeding Birds in the Czech Republic 2014-2017, we modeled species richness at two spatial resolutions of approx. 131 km 2 (large squares) and 8 km 2 (small squares). As predictors of the richness, we assessed 1) classified land cover data (Corine Land Cover 2018 database), 2) spectral heterogeneity (computed in three ways) and landscape composition derived from unclassified remote-sensed reflectance and vegetation indices. Furthermore, we integrated information about the landscape types (expressed by the most prevalent land cover class) into models based on unclassified remote-sensed data to investigate whether the landscape type plays a role in explaining bird species richness. We found that unclassified remote-sensed data, particularly spectral heterogeneity metrics, were better predictors of bird species richness than classified land cover data. The best results were achieved by models that included interactions between the unclassified data and landscape types, indicating that relationships between bird diversity and spectral heterogeneity vary across landscape types. Our findings demonstrate that spectral heterogeneity derived from unclassified multispectral data is effective for assessing bird diversity across the Czech Republic. When explaining bird species richness, it is important to account for the type of landscape and carefully consider the significance of the chosen spatial scale., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Author(s).)

Because of their peculiar but intriguing photophysical properties, peridinin–chlorophyll–protein complexes (PCPs), the peripheral light-harvesting antenna complexes of photosynthetic dinoflagellates have been unique targets of multidimensional theoretical and experimental investigations over the last few decades. The major light-harvesting chlorophyll a (Chl a) pigments of PCP are hypothesized to be spectroscopically heterogeneous. To study the spectral heterogeneity in terms of electrostatic parameters, we, in this study, implemented Stark fluorescence spectroscopy on PCP isolated from the dinoflagellate Amphidinium carterae. The comprehensive theoretical modeling of the Stark fluorescence spectrum with the help of the conventional Liptay formalism revealed the simultaneous presence of three emission bands in the fluorescence spectrum of PCP recorded upon excitation of peridinin. The three emission bands are found to possess different sets of electrostatic parameters with essentially increasing magnitude of charge-transfer character from the blue to redder ones. The different magnitudes of electrostatic parameters give good support to the earlier proposition that the spectral heterogeneity in PCP results from emissive Chl a clusters anchored at a different sites and domains within the protein network. [ABSTRACT FROM AUTHOR]

Plant spectral diversity – how plants differentially interact with solar radiation – is an integrator of plant chemical, structural, and taxonomic diversity that can be remotely sensed. We propose to measure spectral diversity as spectral variance, which allows the partitioning of the spectral diversity of a region, called spectral gamma (γ) diversity, into additive alpha (α; within communities) and beta (β; among communities) components. Our method calculates the contributions of individual bands or spectral features to spectral γ‐, β‐, and α‐diversity, as well as the contributions of individual plant communities to spectral diversity. We present two case studies illustrating how our approach can identify 'hotspots' of spectral α‐diversity within a region, and discover spectrally unique areas that contribute strongly to β‐diversity. Partitioning spectral diversity and mapping its spatial components has many applications for conservation since high local diversity and distinctiveness in composition are two key criteria used to determine the ecological value of ecosystems. [ABSTRACT FROM AUTHOR]

Covering 30%–40% of the terrestrial surface, grasslands are important hosts of biodiversity, crucial for nutrient cycles and carbon sequestration. However, these ecosystems face a pressing threat in the form of biodiversity loss, which can disrupt their functioning and resilience. Addressing this challenge requires effective monitoring of biodiversity changes on large scales. Remote sensing emerges as a valuable tool in this endeavour, enabling the assessment of grassland biodiversity through the analysis of vegetation patterns, species composition, and ecosystem health over extensive areas. According to the spectral variation hypothesis (SVH), the link between pixel-to-pixel spectral variation and species diversity in remote sensing images can be used to retrieve plant diversity based on spectral data. Nevertheless, the transferability of the proposed relation across ecosystem types, seasons and spatial resolutions remains unclear. The absence of comprehensive data has hindered systematic assessments of the SVH so far, which would ideally incorporate coherent sets of diversity estimates from remote sensing data and in-situ plant diversity measurements. With this study, we present a combined approach that brings together trait data from field measurements, simulations of spatial species distributions and radiative transfer models for a systematic and in-depth analysis of the SVH in temperate grasslands. Based on simulated grassland communities with different diversity levels, we assessed the spectral-to-species diversity relationship across (1) three temperate grassland types, (2) three seasons and, (3) five spatial resolutions (from 10 m to 0.2 m pixel size). We used the mean Euclidean distance and Rao's Q as measures for spectral diversity and different biodiversity indices to describe the species and trait diversity of the simulated grassland communities. Based on 45000 simulated grassland communities in five different spatial resolutions, we found that the spectral-to-species diversity relationship is not stable across grassland types and seasons, despite the spectral diversity metric used. Correlations with spectral diversity were inconsistent for the different applied diversity indices and no single index outperformed the others. Spectral diversity was mainly driven by the spatial resolution (i.e. pixel size) of the image and not by species richness (SR) or functional trait diversity (FD) per se. Our results further underline that the link between SR and FD is not always prominent in plant communities and the basic assumption of the SVH is fulfilled only under certain conditions. Consequently, we argue that FD, which is an important driver of the spectral signature of a plant community, is not inevitably linked to the number of present species in an image. We conclude that the interplay of SR and FD is crucial for the expression of the spectral-to-species diversity relationship. This study clearly underlines the context-dependency of the SVH and we point out that, although of promising value for distinct ecosystems, it is not universally applicable in grasslands. • Pixel-to-pixel spectral variation is often treated as biodiversity indicator. • We present a systematic test of the spectral variation hypothesis in grasslands. • Grassland simulations and radiative transfer models were used to bridge the data lack. • We observe that spectral diversity is mainly driven by spatial resolution. • Species richness is not necessarily linked to optical trait diversity. [ABSTRACT FROM AUTHOR]

Plant diversity (PD) plays an important role in maintaining the healthy function of an ecosystem through affecting the productivity, stability, and nutrient utilization of a terrestrial ecosystem. Remote sensing is a vital way to monitor the status and changes of PD. Most of the existing methods rely on a field botany survey to construct a statistical relationship between PD and remote sensing observations. However, a field botany survey is too costly to be applied widely. In this study, we constructed a new remote sensing index of PD (RSPD), combining the spectral variation hypothesis and productivity hypothesis. Concretely, the RSPD integrated the multi-band spectral reflectance and several spectral greenness, moisture, and red-edge vegetation indices with the principles of Shannon information entropy and Euclidean distance. The RSPD was evaluated by comparing the classical coefficient of variation (CV) method and the Shannon and Simpson diversity indices based on vegetation classification results. Two cases were selected, where Case I was in Beijing and Case II was located in part of Huai’an, China. Sentinel-2 data in three years of 2016, 2018, and 2020 and higher-resolution Pléiades-1 data in 2018 were also utilized. The results demonstrate that: (1) the RSPD is basically consistent with the CV in spatiotemporal variation; (2) the RSPD outperforms the CV as compared with Shannon and Simpson diversity indices that are based on vegetation classification results with Sentinel-2 and Pléiades-1 data; (3) the RSPD outperforms the CV as compared with visual interpretations with Google Earth image. The suggested index can reflect the richness and evenness of plant species, which is inherent in its calculation formula. Moreover, it has a great potential for large-scale regional and long-term series monitoring.

The emergence of the spectral variation hypothesis (SVH) has gained widespread attention in the remote sensing community as a method for deriving biodiversity information from remotely sensed data. SVH states that spectral heterogeneity on remotely sensed imagery reflects environmental heterogeneity, which in turn is associated with high species diversity and, therefore, could be useful for characterizing landscape biodiversity. However, the effect of phenology has received relatively less attention despite being an important variable influencing plant species spectral responses. The study investigated (i) the effect of phenology on the relationship between spectral heterogeneity and plant species diversity and (ii) explored spectral angle mapper (SAM), the coefficient of variation (CV) and their interaction effect in estimating species diversity. Stratified random sampling was adopted to survey all tree species with a diameter at breast height of > 10 cm in 90 × 90 m plots distributed throughout the study site. Tree species diversity was quantified by the Shannon diversity index (H′), Simpson index of diversity (D2) and species richness (S). SAM and CV were employed on Landsat-8 data to compute spectral heterogeneity. The study applied linear regression models to investigate the relationship between spectral heterogeneity metrics and species diversity indices across four phenological stages. The results showed that the end of the growing season was the most ideal phenological stage for estimating species diversity, following the SVH concept. During this period, SAM and species diversity indices (S, H′, D2) had an r2 of 0.14, 0.24, and 0.20, respectively, while CV had an r2 of 0.22, 0.22, and 0.25, respectively. The interaction of SAM and CV improved the relationship between the spectral data and H′ and D2 (from r2 of 0.24 and 0.25 to r2 of 0.32 and 0.28, respectively) at the end of the growing season. The two spectral heterogeneity metrics showed differential sensitivity to components of plant diversity. SAM had a high relationship with H′ followed by D2 and then a lower relationship with S throughout the different phenological stages. Meanwhile, CV had a higher relationship with D2 than other plant diversity indices and its relationship with S and H′ remained similar. Although the coefficient of determination was comparatively low, the relationship between spectral heterogeneity metrics and species diversity indices was statistically significant (p < 0.05) and this supports the assertion that SVH could be implemented to characterize plant species diversity. Importantly, the application of SVH should consider (i) the choice of spectral heterogeneity metric in line with the purpose of the SVH application since these metrics relate to components of species diversity differently and (ii) vegetation phenology, which affects the relationship that spectral heterogeneity has with plant species diversity.

Grasslands represent a significant source of biodiversity that is important to monitor over large extents. The Spectral Variation Hypothesis (SVH) assumes that the Spectral Heterogeneity (SH) measured from remote sensing data can be used as a proxy for species diversity. Here, we argue the hypothesis that the grassland’s species differ in their phenology and, hence, that the temporal variations can be used in addition to the spectral variations. The purpose of this study is to attempt verifying the SVH in grasslands using the temporal information provided by dense Satellite Image Time Series (SITS) with a high spatial resolution. Our method to assess the spectro-temporal heterogeneity is based on a clustering of grasslands using a robust technique for high dimensional data. We propose new SH measures derived from this clustering and computed at the grassland level. We compare them to the Mean Distance to Centroid (MDC). The method is experimented on 192 grasslands from southwest France using an intra-annual multispectral SPOT5 SITS comprising 18 images and using single images from this SITS. The combination of two of the proposed SH measures—the within-class variability and the entropy—in a multivariate linear model explained the variance of the grasslands’ Shannon index more than the MDC. However, there were no significant differences between the predicted values issued from the best models using multitemporal and monotemporal imagery. We conclude that multitemporal data at a spatial resolution of 10 m do not contribute to estimating the species diversity. The temporal variations may be more related to the effect of management practices. [ABSTRACT FROM AUTHOR]

No consensus has been yet achieved among Life Cycle Assessment (LCA) practitioners on how to assess the impact on biodiversity due to land uses and land use changes, in particular with regard to agricultural areas. In the domain of nature conservation and landscape ecology, spectral heterogeneity (SH) derived from remotely sensed imagery is considered a viable proxy for species diversity detection. The assessment rationale is based on the ‘spectral variation hypothesis’: the higher the spectral variability, the higher the ecological heterogeneity and species community diversity, occupying different niches. Our hypothesis is that SH can be effective to improve or complement current Life Cycle Impact Assessment−LCIA practice on biodiversity loss evaluation driven by land use. Hence, we aim here to explore this assumption by computing SH at a local scale of crops cultivation in Southern Alps (Trentino province, Italy), and then combining this information with land use over 30 years. We observe and analyse the relationships between land cover maps and habitat heterogeneity at different time and spatial resolutions. This allows us to argue about the robustness of SH to be a potential surrogate of environmental nuances for species variability detection in LCIA. [ABSTRACT FROM AUTHOR]

Measuring heterogeneity in satellite imagery is an important task to deal with. Most measures of spectral diversity have been based on Shannon Information theory. However, this approach does not inherently address different scales, ranging from local (hereafter referred to alpha diversity) to global scales (gamma diversity). The aim of this paper is to propose a method for measuring spectral heterogeneity at multiple scales based on rarefaction curves. An algorithmic solution of rarefaction applied to image pixel values (Digital Numbers, DNs) is provided and discussed.

Grasslands represent a significant source of biodiversity that is important to monitor over large extents. The Spectral Variation Hypothesis (SVH) assumes that the Spectral Heterogeneity (SH) measured from remote sensing data can be used as a proxy for species diversity. Here, we argue the hypothesis that the grassland’s species differ in their phenology and, hence, that the temporal variations can be used in addition to the spectral variations. The purpose of this study is to attempt verifying the SVH in grasslands using the temporal information provided by dense Satellite Image Time Series (SITS) with a high spatial resolution. Our method to assess the spectro-temporal heterogeneity is based on a clustering of grasslands using a robust technique for high dimensional data. We propose new SH measures derived from this clustering and computed at the grassland level. We compare them to the Mean Distance to Centroid (MDC). The method is experimented on 192 grasslands from southwest France using an intra-annual multispectral SPOT5 SITS comprising 18 images and using single images from this SITS. The combination of two of the proposed SH measures—the within-class variability and the entropy—in a multivariate linear model explained the variance of the grasslands’ Shannon index more than the MDC. However, there were no significant differences between the predicted values issued from the best models using multitemporal and monotemporal imagery. We conclude that multitemporal data at a spatial resolution of 10 m do not contribute to estimating the species diversity. The temporal variations may be more related to the effect of management practices.

Abstract: Maps based on classified Earth observation (EO) imagery have been used to model biodiversity, but errors associated with the classification process itself and the resulting discretization of land cover may ultimately limit such efforts. Among other issues, discrete land cover maps can often be costly to produce and validate. Alternatively, the original continuous spectral information in EO imagery can be used. The primary objective of this study was to compare predictors based on continuous and discrete information derived from Landsat TM imagery for modeling biodiversity in agricultural landscapes. In 46 landscapes throughout Eastern Ontario, Canada, landscape metrics (mean field size, the percentage of landscape in agriculture, and crop diversity) derived from a discrete image classification, along with several measures of crop productivity based on the continuous Normalized Difference Vegetation Index (NDVI), were used as predictors of field-based measures of species diversity for birds, butterflies, and plants. Using an Information-Theoretic approach for model-averaging and inference, we compared and interpreted the magnitude and direction of model-averaged coefficients, model evidence ratios, and overall fit of model-averaged predictions. Our findings indicate that when using Landsat TM imagery in agricultural environments, models using predictors derived from continuous information consistently outranked models based on discrete information derived from classified imagery. [Copyright &y& Elsevier]

Here we report the remarkable anatomy of the eye of the Eastern Pale Clouded yellow butterfly, Colias erate. An ommatidium of C. erate bears nine photoreceptors, R1-9, which together form a tiered and fused rhabdom. The distal tier of the rhabdom consists of the rhabdomeral microvilli of R1-4 photoreceptors, R5-8 photoreceptors contribute the proximal tier, and the R9 photoreceptor adds a few microvilli at the base. In transverse sections, four spots of red pigment surrounding the rhabdom are evident in the ventral region of the eye. The red pigment acts as a strong red filter for the proximal photoreceptors. The arrangement of the pigment spots distinguishes the ommatidia into three types: trapezoidal (type I), square (type II) and rectangular (type Ill). In all types of ommatidia, the distal and the proximal tiers of the rhabdom are divided by a strong constriction, clearly to enhance the filtering effect of the red pigment. The ommatidial heterogeneity can also be observed by optical measurements. The eye shine, resulting from tapetal reflections, peaks in type I ommatidia at 660nm, and in type II and III ommatidia at 730nm. The far-redpeaking eye shine indicates that C. erate has far-red-sensitive photoreceptors. Type I ommatidia fluoresce under violet excitation, implying the presence of a violet-absorbing pigment that acts as a short-wavelength filter. [ABSTRACT FROM AUTHOR]

Measuring heterogeneity in satellite imagery is an important task to deal with. Most measures of spectral diversity have been based on Shannon Information theory. However, this approach does not inherently address different scales, ranging from local (hereafter referred to alpha diversity) to global scales (gamma diversity). The aim of this paper is to propose a method for measuring spectral heterogeneity at multiple scales based on rarefaction curves. An algorithmic solution of rarefaction applied to image pixel values (Digital Numbers, DNs) is provided and discussed. [ABSTRACT FROM AUTHOR]

Abstract: We have used phosphorescence from erythrosin B to characterize the molecular mobility and dynamic heterogeneity in dry films of amorphous lactose and lactitol from −25 to 120 °C. The phosphorescence emission spectra red-shifted and broadened with temperature in both sugars, indicating that both the rate of dipolar relaxation and the extent of inhomogeneous broadening increased dramatically at higher temperature. Phosphorescence intensity decays were well fit using a stretched exponential decay model; the rate constant for non-radiative quenching due to collisions with the matrix was calculated from the lifetimes. Arrhenius plots of this rate were non-linear, increasing very gradually at low and dramatically at high temperatures in both sugars. The rate of quenching was significantly lower in a 1:1 (wt/wt) mixture of lactose/lactitol in both the glass and the melt, providing strong evidence that specific interactions within the mixture lowered the matrix mobility. The lifetimes varied systematically with emission wavelength in both matrixes; analysis of the temperature dependence indicated that the activation energy for non-radiative quenching of the triplet state varied somewhat with emission wavelength. Time-resolved emission spectra collected as a function of delay time following pulsed excitation exhibited significant shifts to higher energy as a function of time. These data support a photophysical model in which erythrosin B molecules are distributed among matrix sites that vary such that blue-emitting sites with slower rates of matrix dipolar relaxation also have slower rates of molecular collisions. The amorphous matrixes of lactose and lactitol in both the glass and the melt state are thus characterized by dynamic site heterogeneity in which different sites vary in terms of their overall molecular mobility. [Copyright &y& Elsevier]

Abstract: We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in thin films of either maltose or maltitol to investigate the physical properties of these amorphous pure sugar matrixes. Intensity decays collected as a function of emission wavelength over the range from 640 to 720nm were analyzed using a stretched exponential kinetic model in which the lifetime (τ) and the stretching exponent (β) were the physically relevant parameters. The lifetimes varied systematically with emission wavelength in both matrixes. Analysis of the temperature dependence of the lifetime at each wavelength provided an estimate of the activation energy for nonradiative quenching of the triplet state; the activation energy also varied with emission wavelength. In addition, time-resolved emission spectra exhibited a blue shift with time following excitation. These data support a photophysical model in which probes are distributed among sites that vary in terms of overall molecular mobility and in which sites with lower rates of dipolar relaxation also have lower rates of collisional quenching of the erythrosin triplet state. The amorphous matrix of both maltose and maltitol in both the glass and the melt state is thus characterized by dynamic site heterogeneity in which different sites vary in terms of their overall molecular mobility. [Copyright &y& Elsevier]

Plant diversity (PD) plays an important role in maintaining the healthy function of an ecosystem through affecting the productivity, stability, and nutrient utilization of a terrestrial ecosystem. Remote sensing is a vital way to monitor the status and changes of PD. Most of the existing methods rely on a field botany survey to construct a statistical relationship between PD and remote sensing observations. However, a field botany survey is too costly to be applied widely. In this study, we constructed a new remote sensing index of PD (RSPD), combining the spectral variation hypothesis and productivity hypothesis. Concretely, the RSPD integrated the multi-band spectral reflectance and several spectral greenness, moisture, and red-edge vegetation indices with the principles of Shannon information entropy and Euclidean distance. The RSPD was evaluated by comparing the classical coefficient of variation (CV) method and the Shannon and Simpson diversity indices based on vegetation classification results. Two cases were selected, where Case I was in Beijing and Case II was located in part of Huai'an, China. Sentinel-2 data in three years of 2016, 2018, and 2020 and higher-resolution Pléiades-1 data in 2018 were also utilized. The results demonstrate that: (1) the RSPD is basically consistent with the CV in spatiotemporal variation; (2) the RSPD outperforms the CV as compared with Shannon and Simpson diversity indices that are based on vegetation classification results with Sentinel-2 and Pléiades-1 data; (3) the RSPD outperforms the CV as compared with visual interpretations with Google Earth image. The suggested index can reflect the richness and evenness of plant species, which is inherent in its calculation formula. Moreover, it has a great potential for large-scale regional and long-term series monitoring. [ABSTRACT FROM AUTHOR]

The emergence of the spectral variation hypothesis (SVH) has gained widespread attention in the remote sensing community as a method for deriving biodiversity information from remotely sensed data. SVH states that spectral heterogeneity on remotely sensed imagery reflects environmental heterogeneity, which in turn is associated with high species diversity and, therefore, could be useful for characterizing landscape biodiversity. However, the effect of phenology has received relatively less attention despite being an important variable influencing plant species spectral responses. The study investigated (i) the effect of phenology on the relationship between spectral heterogeneity and plant species diversity and (ii) explored spectral angle mapper (SAM), the coefficient of variation (CV) and their interaction effect in estimating species diversity. Stratified random sampling was adopted to survey all tree species with a diameter at breast height of > 10 cm in 90 × 90 m plots distributed throughout the study site. Tree species diversity was quantified by the Shannon diversity index (H′), Simpson index of diversity (D2) and species richness (S). SAM and CV were employed on Landsat-8 data to compute spectral heterogeneity. The study applied linear regression models to investigate the relationship between spectral heterogeneity metrics and species diversity indices across four phenological stages. The results showed that the end of the growing season was the most ideal phenological stage for estimating species diversity, following the SVH concept. During this period, SAM and species diversity indices (S, H′, D2) had an r2 of 0.14, 0.24, and 0.20, respectively, while CV had an r2 of 0.22, 0.22, and 0.25, respectively. The interaction of SAM and CV improved the relationship between the spectral data and H′ and D2 (from r2 of 0.24 and 0.25 to r2 of 0.32 and 0.28, respectively) at the end of the growing season. The two spectral heterogeneity metrics showed differential sensitivity to components of plant diversity. SAM had a high relationship with H′ followed by D2 and then a lower relationship with S throughout the different phenological stages. Meanwhile, CV had a higher relationship with D2 than other plant diversity indices and its relationship with S and H′ remained similar. Although the coefficient of determination was comparatively low, the relationship between spectral heterogeneity metrics and species diversity indices was statistically significant (p < 0.05) and this supports the assertion that SVH could be implemented to characterize plant species diversity. Importantly, the application of SVH should consider (i) the choice of spectral heterogeneity metric in line with the purpose of the SVH application since these metrics relate to components of species diversity differently and (ii) vegetation phenology, which affects the relationship that spectral heterogeneity has with plant species diversity. [ABSTRACT FROM AUTHOR]

The unprecedented global biodiversity loss has massive implications for the capacity of ecosystems to maintain functions critical to human well‐being, urgently calling for rapid, scalable, and reproducible strategies for biodiversity monitoring, particularly in threatened ecosystems with difficult field access such as wetlands. Remote sensing indicators of spectral variability and greenness may predict the diversity of plant communities based on their optical diversity; however, most evidence is based on narrowband spectral data or terrestrial ecosystems. We investigate how spectral greenness and heterogeneity from publicly available broadband multi‐spectral Landsat satellite imagery explain variation in vegetation diversity across different wetland types, ecoregions, and disturbance levels using 1,138 sites surveyed by U.S. EPA's National Wetland Condition Assessment. We found positive correlations of plant species richness and diversity with indicators of annual maximum spectral greenness and its spatial heterogeneity, explaining up to 43% variation within the global sample, 48% within wetland types or ecoregions, and up to 61% with abiotic covariates. The combined effect of spectral greenness and heterogeneity was stronger than the best‐performing model using climatic, topographic, and edaphic factors alone. When compared among major U.S. watersheds and individual states, the fit of diversity‐greenness models increased when more wetland types were included within the corresponding region's boundaries, up to 61% at the watershed and 77% at the state level, respectively, for diversity models and up to 73% and 80%, respectively, for richness models. Model outliers were characterized by a significantly greater diversity of nonnative species (P < 0.0001), suggesting that changes in model performance and greenness distributions could be used as indicators of shifts in plant community composition, particularly in tidal wetlands making the majority of outliers with significantly lower than predicted diversity. This study represents a first‐time national‐scale effort to use publicly available remote sensing, climatic, and topographic data to predict plant diversity in wetlands, which tend to be understudied compared to terrestrial ecosystems despite being among the most stressed ecosystems on Earth. Our study suggests that multi‐temporal broadband satellite imagery could provide a low‐cost assessment of regional and national wetland biodiversity for prioritization of conservation efforts and early detection of biodiversity loss. [ABSTRACT FROM AUTHOR]

Biodiversity is essential to healthy ecosystem function, influencing productivity and resilience to disturbance. Biodiversity loss endangers essential ecosystem services and risks unacceptable environmental consequences. Global biodiversity observations are needed to provide a better understanding of the distribution of biodiversity, to better identify high priority areas for conservation and to help maintain essential ecosystem goods and services. Traditional in situ biodiversity monitoring is limited in time and space and is usually a costly and time-consuming enterprise. Remote sensing can provide data over a large area in a consistent, objective manner and has been used to detect plant biodiversity in a range of ecosystems, typically based on relating spectral properties to the distribution of habitat, species or functional groups. Recent years have witnessed the emergence of methods using imaging spectroscopy to assess biodiversity via plant traits or spectral information content. However, questions regarding the complex drivers of plant optical properties and the scale dependence of spectral diversity – biodiversity relationship confound diversity monitoring using remote sensing and must first be better understood before these methods can be operationally applied. To address some of these topics, we (1) review the history of remote sensing approaches in biodiversity estimation, summarizing the pros and cons of different methods, (2) illustrate successes and major gaps of remote sensing of biodiversity, and (3) identify promising future directions. We focus on emerging methods using spectral diversity (optical diversity) as a proxy for terrestrial plant diversity that offer to revolutionize the study of diversity in its different dimensions (phylogenetic, taxonomic, and functional diversity) from remote sensing. We also discuss remaining knowledge gaps and ways spectral diversity might be effectively integrated into a global biodiversity monitoring system, bridging a gap between ecology and remote sensing. • We review the history of remote sensing approaches for biodiversity estimation. • We summarize the pros and cons of different methods in remote sensing of plant biodiversity. • A particular focus relates spectral diversity to biodiversity at different scales. • Major gaps are discussed in the context of a global biodiversity monitoring system. [ABSTRACT FROM AUTHOR]

We report measurements of excitation and emission spectra of single, polymer-embedded, perylene dye molecules at room temperature. From these measurements, we can derive the Stokes shift for each single molecule. We determined the distribution of excitation and emission peak energies and, thus, the distribution of single molecule Stokes shifts. Single molecule Stokes shifts have not been recorded to date, and the Stokes shift has often been assumed to be constant in single molecule studies. Our data show that the observed spectral heterogeneity in single molecule emission originates not only from synchronous energetic shifts of the excitation and the emission spectra but also from variations in the Stokes shift, speaking against the assumption of constant Stokes shift.