Effects of heavy metals on the absorbance and reflectance spectra of plants

Abstract.

Published work on the reflectance of vegetation growing over soil mineralizations is reviewed. Experimental work was carried out on several species grown in a glasshouse and was extended to a pilot field study. In the laboratory studies, the most general effects of Cd, Cu, Pb or Zn were growth inhibition. A detailed study of the leaf pigments of pea plants showed that the chl a/chl b ratio (chl=chlorophyll) decreased under conditions of Cd or Cu stress but showed little effect with Pb or Zn. However, the absorption spectra of chloroplast pigments were not found to show any wavelength shifts with metal treatments, indicating that new spectral forms of chlorophyll were not produced as a stress response. A decrease in the total chlorophyll content of leaf tissue (fresh weight basis) was correlated with an increase in visible-wavelength leaf reflectance (R) of pea plants. R at infrared wavelengths of 0.85 μm, 1.65 μm and 2.20 μm decreased in metal-treated plants, compared with controls. Although experiments with other species, and a review of published literature, indicate that reflectance effects are dependent on species, phase of growth cycle and environment, the existence of correlations between R at certain wavelengths and the metal concentrations to which roots are exposed was confirmed using oak trees growing naturally in the area of a copper-arsenic mineralization in south-west England. Metal (Cu or As) concentrations in the soil were strongly negatively correlated (p > 99 per cent) with R at 1.65 μm and 2.20 μm, and positively correlated (p > 95 per cent) with R at 0.660 μm, in close agreement with the experiments on pea plants. The inclusion of the relevant infrared bands on Earth resource survey instruments is likely to enhance their usefulness for detecting heavy metal stress in plants.     

Variability of high-resolution crop reflectance spectra

Abstract

High-spectral-resolution reflectance spectra from ground and helicopter measurements of agricultural crops and soils were analyzed to determine spectral variability in the visible and near-infrared (0 4-2 38 μm), using a procedure previously applied to thermal infrared emittance spectra of the atmosphere and to reflectance spectra of soil samples. Five spectral basis functions were sufficient to describe separately the ground and helicopter data, six or, at most, seven are sufficient to describe the pooled data. Thus, five to seven relatively broad band measurements, together with basis functions developed in this analysis, are sufficient to describe the variability of both data sets, to within differences that are probably associated with the measurement process and instrument noise.     

重金属捕集剂二甲基二硫代氨基甲酸对6种重金属螯合固化性能的量子化学研究

为探讨二甲基二硫代氨基甲酸盐螯合重金属离子的作用机理,本文采用密度泛函理论,在B3LYP/6-31++G（d,p）和B3LYP/LanL2DZ混合基组水平上,分别计算了二甲基二硫代氨基甲酸离子（DDC^-）和铬、铜、钴、锌、铁、镉6种重金属离子形成配合物的前线轨道能级、配位能△E、考虑基组重叠误差后的配位能△E_BSSE、零点振动能校正后的配位能△E_ZPE及自然电荷分布。研究结果表明:上述二甲基二硫代氨基甲酸配合物的稳定性与能级差△ε及配位能△E_BSSE、△E_ZPE的绝对值密切相关,△ε及△E_BSSE、△E_ZPE的绝对值越大,配合物越稳定。6种二甲基二硫代氨基甲酸重金属配合物的稳定性由大到小的顺序为:[CrDDC]²⁺>[CuDDC]⁺>[CoDDC]⁺>[ZnDDC]⁺>[FeDDC]⁺>[CdDDC]⁺。在形成配合物的过程中,电子从配体DDC^-流向重金属离子,电荷转移越多,配位能的绝对值越大。     

Variability of biome reflectance directional signatures as seen by POLDER

Reflectance measurements acquired with the spaceborne POLDER instrument are used to analyze the variability of land surface directional signatures as a function of vegetation cover type. The reflectance directional signatures are quantified by the three parameters of a modified version of the Ross-Li reflectance model. The variability of the estimated parameters with respect to the seven MODIS biome classes was found to be higher within the classes than between classes, with the exception of the desert targets that show more isotropic reflectances. A limited number of standard BRDFs (typically 5 in the red and near infrared) capture most of the variability of the directional reflectance measurements, supporting the idea that different land surfaces have similar directional signatures. Over vegetation targets, they are characterized by a strong increase toward backscattering and much smaller variations in forward directions. The results express the diversity in structural situations within a given biome class and indicate that, at the resolution of the POLDER sensor, i.e. a few kilometers, the BRDF contains little information on the dominant vegetation type. We show that standard directional signatures may be used to correct the reflectance measurements for directional effects with an RMS error on the order of 0.011 in the red and 0.015 in the near infrared.     

Computer simulation of the skin reflectance spectra

The reflectance spectra of the human skin in visible and near-infrared (NIR) spectral region have been calculated using the Monte Carlo technique, and the specular and internal reflection on the medium surface is taken into account. Skin is represented as a complex inhomogeneous multi-layered highly scattering and absorbing medium. The model takes into account variations in spatial distribution of blood, index of blood oxygen saturation, volume fraction of water and chromophores content. The simulation of the skin tissues optical properties and skin reflectance spectra are discussed. Comparison of the results of simulation and in vivo experimental results are given.     

Fourth derivative analysis of Red Sea coral reflectance spectra

Reflectance spectra of coral colonies and associated sand and rubble were obtained over the fringing reefs of Eilat, Israel using two GER 1500 radiometers. The overall spectral response curve of Red Sea corals displayed the same three inflection points reported for Pacific corals, with notable differences between in vitro and in situ measurements. Fourth derivative analysis of relatively pure spectra (filling the sensor's field of view) allowed for differentiation of coral and non-coral targets with 95–99% accuracy. The characteristic peaks revealed by the fourth derivative match those obtained on Hawaiian corals.     

Spectral reflectance changes accompanying a post-fire recovery sequence in a subarctic spruce lichen woodland

A sequence of burned surfaces aged 0, 1, 2, 25 and 80 years was investigated regarding changes in the spectral distribution of reflected light. Controls were introduced to isolate diurnal and seasonal effects. The results show gradually increasing reflectance with increasing age of burn. With the establishment of vegetation a new set of absorption and reflectance criteria are established substantially altering the spectral characteristics. The apparent effect of a mature forest canopy is ambiguous. Diffuse and overcast conditions reduce the reflectance for all surfaces. Further work is suggested to reinforce results for surfaces with low sampling replication.     

Spectral unmixing of normalized reflectance data for the deconvolution of lichen and rock mixtures

In subarctic regions the ubiquitous presence of rock encrusting lichens compromises the ability to map the reflectance signatures of minerals from imaging spectrometer data. The use of lichen as an endmember in spectral mixture analysis (SMA) may overcome these limitations. Because lichens rarely completely occupy the Instantaneous Field of View (IFOV), it is difficult to define a lichen endmember from an image using visual or automated endmember extraction tools. Spectral similarity of various crustose/foliose lichen species in the short wave infrared (SWIR) suggests that spectral unmixing of rock and lichens may be successfully accomplished using a single lichen endmember for this spectral range. We report the use of a spectral normalization method to minimize differences in SWIR reflectance between five lichen species (U. torrefacta, R. bolanderi, R. geminatum, R. geographicum, A. cinerea). When the normalization is applied to reflectance spectra from 2000-2400 nm acquired for a lichen encrusted quartzite rock sample we show that only a single lichen endmember is required to account for the lichen contribution in the observed mixtures. In contrast, two such endmembers are required when the normalization is not applied to the reflectance data. We illustrate this point using examples where endmembers are extracted manually and automatically, and compare the SMA results against abundances estimated from digital photography. For both the reflectance and normalized reflectance data, SMA results correlate well (R²>0.9) with abundances estimated from digital photography. The use of normalized reflectance implies that any field/laboratory lichen spectrum can be selected as the lichen endmember for SMA of airborne/spaceborne imagery.     

Effects of lichens on the reflectance spectra of granitic rock surfaces

The objective of this study was to determine the effect of lichen cover on the spectral reflectance characteristics of granitic rocks. Rock samples collected from bedrock exposures and talus slopes were granodiorite, tonalite, granite, and quartz-diorite. The lichens found on these rocks varied in color, i.e., black, dark brown, medium gray, olive-green, yellow-green, green, orange, and orange-red. The visible and near infrared reflectance spectra (400–1100 nm) of the rock and lichen samples show that lichens can affect the rock's spectra. These changes are dependent on the reflectance contrast between the rock surface and the lichen covering.     

A multi-angle spectrometer for automatic measurement of plant canopy reflectance spectra

The paper describes the design and operation of a multi-angle spectrometer (MAS) for automatic measurement of near-field spectral reflectances of plant canopies at hourly intervals. A novel feature of the instrument is a rotating periscope connected to a spectrometer via a fiber optic cable. Canopy reflectances are calculated for multiple view azimuths, at a single zenith angle from measurements of spectrometer dark current, incoming solar irradiance and reflected radiances. Spectral measurements are made between 300 and 1150 nm wavelength at a band-to-band spacing of 3 nm, and a bandwidth (full-width, half maximum) of 10 nm. Preliminary data analysis showed that the canopy reflectance model of Kuusk [Kuusk, A. (1995). A fast, invertible canopy reflectance model. Remote Sensing of Environment 51, 342-350] reproduced the observed large differences in visible and near-infrared (NIR) reflectances, but the model was unable to predict quantitatively the observed variations in the measured reflectance spectra with azimuth, particularly in the NIR. Discrepancies between model and measurements are likely due to the inhomogeneous nature of the forest canopy in contrast to the assumption of a uniformly absorbing turbid medium in the model. Measurements using the MAS can be used to investigate directional dependences of reflectance indices and for testing BRDF models used to separate geometrical and plant physiological contributions to the reflectance signals. The MAS provides continuous sampling of reflectance indices which can be compared with canopy properties such as chlorophyll content and photosynthetic capacity.     

Retrieval of chlorophyll concentration from leaf reflectance spectra using wavelet analysis

The dynamics of foliar chlorophyll concentrations have considerable significance for plant-environment interactions, ecosystem functioning and crop growth. Hyperspectral remote sensing has a valuable role in the monitoring of such dynamics. This study focussed upon improving the accuracy of chlorophyll quantification by applying wavelet analysis to reflectance spectra. Leaf-scale radiative transfer models were used to generate very large spectral data sets with which to develop and rigorously test refinements to the approach and compare it with existing spectral indices. The results demonstrated that by decomposing leaf spectra, the resultant wavelet coefficients can be used to generate accurate predictions of chlorophyll concentration, despite wide variations in the range of other biochemical and biophysical factors that influence leaf reflectance. Wavelet analysis outperformed predictive models based on untransformed spectra and a range of spectral indices. The paper discusses the possibilities for further refining the wavelet approach and for extending the technique to the sensing of a variety of vegetation properties at a range of spatial scales.     

电化学传感器在水质重金属检测中的应用

中国工业快速发展伴随而来的水质重金属污染问题正日益影响着人们的正常生活,寻求快速准确的水质重金属检测方法是十分迫切的.众多水质检测传感器中,电化学传感器具有检测灵敏、操作简单、成本低、便携等优势,在水质重金属检测领域占据了十分重要地位,拥有广阔的前景.本文重点介绍了用于水质重金属检测的几种电化学传感器,包括它们的构造、分类及其检测原理.并对应用于水质重金属检测的电流型电化学传感器和电位型电化学传感器进行了详细说明,介绍了阳极溶出伏安法和离子选择性电极法在内的几种电化学分析方法,以及近年来相关研究的现状.     

水质重金属检测技术研究进展

水质重金属检测技术的发展对治理水质污染工作具有十分重要的意义.对近年来水质重金属检测技术方法以及该领域的研究进展进行综述,主要介绍了原子吸收光谱法、原子荧光光谱法,电感耦合等离子体法,紫外-可见分光光度法,高效液相色谱法,电化学分析法和生物检测法,对这些技术的工作原理、仪器和特点等方面进行阐述,比其在水质重金属检测过程中的利与弊进行探讨,最后对该领域的研究方向进行了展望.     

Estimating sulphide ore grade in broken rock using visible/infrared hyperspectral reflectance spectra

The field of hyperspectral remote sensing has developed rapidly for widespread mineral mapping from airborne platforms. The purpose of the current study was to examine whether hyperspectral spectrometry (0.35-2.5 w m) can be used in an underground mining environment for mapping the grade of sulphide ore in rock faces, hand specimens and core logging. Naturally broken samples of barren and ore-bearing rocks were collected from mines in the Sudbury Basin, Ontario, and dry and wet reflectance were measured. The sulphide minerals exhibit a one-sided absorption band at short wavelengths known as a conductance band. The hydroxyl-bearing silicates exhibit a triple absorption feature near 2.3 w m. Two ratios, one describing the conductance band and one describing the hydroxyl band, can be used to separate high grade ores (>20-25% sulphides) from barren and lower grade rocks. The conductance band ratio can also be used to estimate the concentration of chalcopyrite alone, - 15% chalcopyrite, absolute. Errors are proportional to the concentration of pyrrhotite and pentlandite. Errors can be reduced if total sulphides are estimated by other means, which a parallel study indicates is possible using thermal reflectance wavelengths. The study indicates that there is a high potential to use hyperspectral tools to grade sulphide ores.     

Identification and mapping of minerals in drill core using hyperspectral image analysis of infrared reflectance spectra

A Portable Infrared Mineral Analyzer II (PIMA II) field spectrometer was used to measure infrared reflectance spectra (1·3-2·5 μm) of split drill core at 1 cm intervals in both the along-core and cross-core directions. These data were formatted into an image cube similar to that acquired by an imaging spectrometer with 600 spectral channels, and multi-spectral and hyperspectral analysis techniques were used for analysis. Colour images and enhancements provided visual displays of the spectral information, while real-time digital extraction of individual spectra allowed identification of minerals. Absorption band-depth mapping and spectral classification were used to map the spatial distribution of specific minerals in the core. Linear spectral unmixing provided estimated mineral abundances. Analysis results demonstrate that multi-spectral and hyperspectral image analysis methods can be used to produce detailed mineralogical maps of drill core. They suggest that the concepts and analytical techniques developed for analysis of hyperspectral image data can be applied to field and laboratory spectra in a variety of disciplines, and raise the question of the use of hyperspectral scanners in the laboratory.     

Exploring the potential of leaf reflectance spectra for retrieving the leaf maximum carboxylation rate

The maximum carboxylation rate (V_cmax) is a key photosynthetic parameter that is determined by the leaf biochemistry and environmental conditions. Numerous studies have shown that plant biochemical, physiological and structural parameters can be estimated from reflectance spectra. Therefore, it is reasonable to assume that V_cmax can be spectrally determined. Here, we investigate the potential of leaf reflectance spectra for retrieving the maximum carboxylation rate of leaves. Measurements of leaf reflectance, carbon dioxide (CO₂) response curves, leaf chlorophyll-a + b (chl-a + b) etc., were made on 80 crop, shrub and tree leaves. Then, the leaf V_cmax,25 was linked to leaf biochemistry and spectral reflectance. A reliable relationship, with a coefficient of determination (R²) value of 0.75, was found between the leaf chl-a + b content and V_cmax,25. The leaf V_cmax,25 values were also significantly correlated with chl-a + b-sensitive spectral indices with the highest R² value that was found being 0.83 for the ratio spectral index (RSI) using reflectances at 1089 nm and 695 nm. Finally, multiple stepwise regression (MSR) and a partial least-squares regression (PLSR) modelling approach were used to estimate V_cmax,25 from leaf reflectances. The results confirmed that V_cmax,25 can be reliably estimated from leaf reflectance spectra and give an R² value >0.80. These findings show that leaf chl-a + b can be used as a proxy for leaf V_cmax,25 and that leaf V_cmax,25 can be spectrally determined using leaf reflectance data.     

重金属离子的光学检测方法综述

研究了环境和食品中重金属离子的检测方法。介绍了电化学分析法等非光学检测方法,较深入地分析了原子吸收光谱法、原子荧光光度法、原子发射光谱法、紫外可见分光光度法、表面等离子体共振技术测量法、试纸—光电反射测量法、共振光散射技术测量法以及激光诱导击穿光谱法等光学检测方法,给出了重金属离子检测的研究重点与发展方向。     

光纤重金属离子传感器的研制

介绍了光纤维重金属离子传感器的研制情况。该传感器将流动注射分析方法和激光激发荧光光谱技术结合起来 ,融合进光纤传导 ,CCD摄像机等技术。对Cu2 +、Cd2 +、Zn2 +及Ni2 +等重金属离子试验研究结果表明 :检测限要低于德国饮用水标准 ,且线性范围宽     

Variability and classification of remote sensing reflectance spectra in the eastern English Channel and southern North Sea

During spring and summer 2004, intensive field bio-optical campaigns were conducted in the eastern English Channel and southern North Sea to assess the mechanisms regulating the ocean color variability in a complex coastal environment. The bio-optical properties of the sampled waters span a wide range of variability, due to the various biogeochemical and physical processes occurring in this area. In-water hyperspectral remote sensing reflectances (R_rs) were acquired simultaneously with measurements of optically significant parameters at 93 stations. An empirical orthogonal function (EOF) analysis indicates that 74% of the total variance of R_rs is partly explained by particulate backscattering (b_bp), while particulate and dissolved absorption only explain 15% of the ocean color variability. These results confirm, for the first time from in situ backscattering measurements, previous studies performed in other coastal environments. Whereas the amplitude factors of the first EOF mode are well correlated (r = 0.75) with the particulate backscattering coefficient (b_bp), the highest correlation (r = 0.83) is found with the particulate backscattering ratio (b_bp/b_p). This result highlights the fundamental role of the nature of the bulk particulate assemblage in the ocean color variability.An unsupervised hierarchical cluster analysis applied to our data set of normalized R_rs spectra, leads to five spectrally distinct classes. We show that the class-specific mean R_rs spectra significantly differ from one another by their bio-optical properties. Three classes particularly stand out: one class corresponds to a Phaeocystis globosa bloom situation, whereas the two others are associated with water masses dominated by mineral and non-living particles, respectively. Among the different bio-optical parameters, the particulate backscattering ratio, the chlorophyll concentration, and the particulate organic carbon to chlorophyll ratio, are the most class-specific ones. These different results are very encouraging for the inversion of bio-optical parameters from class-specific algorithms.     

纳米材料技术在水环境重金属检测中的应用与发展

近年来,纳米材料技术在水环境重金属检测领域中的应用已经成为重要的研究课题.纳米材料特殊的尺寸使其具有优异的物理、化学和光学性能,许多研究者将其应用在水环境重金属检测领域.本文从纳米材料技术在水环境重金属的光学检测与电化学检测两个方面,对纳米材料技术在水环境重金属检测中的应用做出综述并对其发展给予展望.光学检测方面主要对纳米材料在比色分析法和表面增强拉曼散射法检测水环境重金属中应用进行简要叙述;电化学检测方面则是根据纳米材料结构的不同将其分为零维、一维、二维和三维纳米材料,分别对其在水环境重金属检测中的应用与发展进行综述.