Differences In Reflectance Spectra Research Articles

A spectral analysis of common boreal ground lichen species

Lichens dominate a significant part of the Earth's land surface, and are valuable bioindicators of various environmental changes. In the northern hemisphere, the largest lichen biomass is in the woodlands and heathlands of the boreal zone and in tundra. Despite the global coverage of lichens, there has been only limited research on their spectral properties in the context of remote sensing of the environment. In this paper, we report spectral properties of 12 common boreal lichen species. Measurements of reflectance spectra were made in laboratory conditions with a standard spectrometer (350–2500 nm) and a novel mobile hyperspectral camera (400–1000 nm) which was used in a multiangular setting. Our results show that interspecific differences in reflectance spectra were the most pronounced in the ultraviolet and visible spectral range, and that dry samples always had higher reflectance than fresh (moist) samples in the shortwave infrared region. All study species had higher reflectance in the backward scattering direction compared to nadir or forward scattering directions. Our results also reveal, for the first time, that there is large intraspecific variation in reflectance of lichen species. This emphasizes the importance of measuring several replicates of each species when analyzing lichen spectra. In addition, we used the data in a spectral clustering analysis to study the spectral similarity between samples and species, and how these similarities could be linked to different physical traits or phylogenetic closeness of the species. Overall, our results suggest that spectra of some lichen species with large ground coverage can be used for species identification from high spatial resolution remote sensing imagery. On the other hand, for lichen species growing as small assemblages, mobile hyperspectral cameras may offer a solution for in-situ species identification. The spectral library collected in this study is available in the SPECCHIO Spectral Information System.

Detection of postharvest quality loss in broccoli by means of non-colorimetric reflection spectroscopy and hyperspectral imaging

Broccoli is a highly perishable vegetable. In academia, shelf life of broccoli is generally monitored using colorimetric devices based on diffuse reflection. However, actual quality and storability of a single broccoli curd after harvest remains uncertain before changes are noticed by the human eye. The aim of the present study was to evaluate broccoli quality loss during storage based on differences in reflectance spectra and to judge quality stages prior to color changes. Reflection spectra of broccoli harvested throughout one cultivation period in northern Germany (June–September) and stored at 16°C and 95% relative humidity for four days were analyzed by principal component analysis (PCA). Apart from an overall increase of reflection in the visible range, changes of the spectral signature were limited to the red edge region. Quality and storability of broccoli could sufficiently be rated by the help of the normalized difference vegetation index (NDVI) and the inflection point of the red edge region, respectively. The inflection point was more sensitive to quality changes, while the NDVI was additionally influenced by differences in fertilizer application during cultivation. Analysis of hyperspectral images of broccoli curds showed an increase in both means and variance of Euclidean distances during storage. This applied to the overall VIS spectrum but was most prominent in the range of 530–650nm. The variation could adequately be demonstrated by the help of composite images, when reflection intensities of three different wavelengths (530, 590, and 650nm) were placed as RGB image channels. Means of Euclidean distances were highly correlated with means of the colorimetric parameter b∗ (R2=0.92). Detected variation within the images was most likely based on different senescence status of single florets. However, classification procedures failed to sort the derived information into image classes because reflection intensity increased rather gradually. Further examinations at lower storage temperatures are required in order to clarify if early quality losses might be sooner detected by Euclidean distances in hyperspectral images compared to CIELAB-readings.

Fusion of Difference Images for Change Detection Over Urban Areas

As a result of urbanization, land use/land cover classes in urban areas are changing rapidly, and this trend increased in the recent years. Change information detected from multi-temporal remote sensing images can thus help to understand urban development and to effectively support urban planning. Differences in reflectance spectra, easily obtained by multi-temporal remote sensing images, are important indicators to characterize these changes. Although many algorithms were proposed to generate difference images, the results are usually greatly inconsistent. In order to integrate the merits of different algorithms to recognize spectral changes, fusion techniques merging multiple difference images are proposed and implemented in this paper. Feature and decision level fusion are used to combine simple change detectors, and to build an automatic change detection procedure. The proposed approach is tested with multi-temporal CBERS and HJ-1 images, and experimental results demonstrate its effectiveness and reliability. By integrating different change information, the appropriate fusion method can be selected according to the specific application in order to minimize the omission or the commission errors.

Hyperspectral imaging techniques for rapid identification of Arabidopsis mutants with altered leaf pigment status.

The spectral reflectance signature of living organisms provides information that closely reflects their physiological status. Because of its high potential for the estimation of geomorphic biological parameters, particularly of gross photosynthesis of plants, two-dimensional spectroscopy, via the use of hyperspectral instruments, has been widely used in remote sensing applications. In genetics research, in contrast, the reflectance phenotype has rarely been the subject of quantitative analysis; its potential for illuminating the pathway leading from the gene to phenotype remains largely unexplored. In this study, we employed hyperspectral imaging techniques to identify Arabidopsis mutants with altered leaf pigment status. The techniques are comprised of two modes; the first is referred to as the ‘targeted mode’ and the second as the ‘non-targeted mode’. The ‘targeted’ mode is aimed at visualizing individual concentrations and compositional parameters of leaf pigments based on reflectance indices (RIs) developed for Chls a and b, carotenoids and anthocyanins. The ‘non-targeted’ mode highlights differences in reflectance spectra of leaf samples relative to reference spectra from the wild-type leaves. Through the latter approach, three mutant lines with weak irregular reflectance phenotypes, that are hardly identifiable by simple observation, were isolated. Analysis of these and other mutants revealed that the RI-based targeted pigment estimation was robust at least against changes in trichome density, but was confounded by genetic defects in chloroplast photorelocation movement. Notwithstanding such a limitation, the techniques presented here provide rapid and high-sensitive means to identify genetic mechanisms that coordinate leaf pigment status with developmental stages and/or environmental stress conditions.

AN APPROACH TO INVASIVE AND NON-INVASIVE QUALITY ASSESSMENT ON PLUMS WITH EDIBLE COATINGS

The effects of edible coatings on the shelf life of plums (Prunus salicina Lindl. 'Sapphire') were studied using Semperfresh with/without 0.2% sorbitol as plasticizer. The plums were stored at 20°C and 85% relative humidity. Changes in mass loss, firmness, colour (L * , a * and hue angle), soluble solids content (SSC), pH, titratable acidity, ethylene, CO 2 , malondialdehyde (MDA), and VIS/NIR reflectance spectra were recorded at 2-day intervals. Edible coating with Semperfresh was effective in delaying the increase of pH and MDA and the loss of titratable acidity and L * . The incorporation of sorbitol revealed beneficial effects on flesh firmness after 4 d of storage. However, no significant difference was found in mass loss, SSC, a * , ethylene and CO 2 . Fruit ripening during the experimental period was measurable in the VIS (350-750 nm) and NIR (750-1400 nm) wavelength ranges due to decrease in the fruit chlorophyll content and also water loss, respectively. No differences in reflectance spectra of coated and uncoated plums were observed.

The use of Vis‐NIR spectral reflectance for determining root density: evaluation of ryegrass roots in a glasshouse trial

SummaryThis paper reports the use of visible/near‐infrared reflectance spectroscopy (Vis‐NIRS) to predict pasture root density. A population of varying grass root densities was created by growing Moata ryegrass (Lolium multiflorum Lam.) for 72 days in pots of Ramiha silt loam (Allophanic) and Manawatu fine sandy loam (Recent Fluvial) (60 pots for each soil) differentially fertilized with nitrogen (N) and phosphorus (P) in a glass house experiment. At harvest, the reflectance spectra (350–2500 nm) from flat sectioned horizontal soil slices (1.3 cm depth), taken from 57 selected pots, were recorded using a portable spectroradiometer (ASD FieldSpec Pro, Boulder, CO). Root densities within each of the soil slices were measured using a wet sieving technique. A large variation in root densities (0.46–5.02 mg dry root cm−3) was obtained from the glass house experiment as plant growth responded to the different soils and rates of N and P fertilizer treatment. Pots of the Manawatu soil contained greater ryegrass root densities (1.76–5.02 mg dry root cm−3) than pots of the Ramiha soil (0.46–3.84 mg dry root cm−3). Each soil had visually distinct reflectance spectra in the range 470–2440 nm, but different root masses produced relatively small differences in reflectance spectra. The first two principal components (PC1 and PC2) of a principal component analysis of the first derivative of the spectral reflectance accounted for 71.3% of the spectral variance and clearly separated the Ramiha and Manawatu soils. PC1, which accounted for 58.4% of the spectral variance, was also well correlated to root density. Partial least squares regression (PLSR) of the first derivative of the 10 nm spaced spectral data against measured root densities produced calibration models that allowed quantitative estimates of root densities (without removing outlier, r2 cross‐validation = 0.78, ratio of prediction to deviation (RPD) = 2.14, root mean squares error of cross‐validation (RMSECV) = 0.60 mg cm−3; with removing outliers, r2 cross‐validation = 0.85, RPD = 2.63, RMSECV = 0.47 mg cm−3). The study indicated that spectral reflectance measurement has the potential to quantify root density in soils.

Alteration of hydrovolcanic basaltic ash: Observations with visible and near‐infrared spectrometry

Ash of basaltic composition that is produced by hydrovolcanic activity occurs frequently on Earth and may be much more widespread on Mars. Altered basaltic tephras from tuff rings and tuff cones across the Basin and Range were examined using visible and near infrared (Vis/IR) reflectance spectrometry and a variety of other techniques. It was found that Vis/IR Spectrometry is sensitive to subtle changes in the hydration and oxidation state of these tephras. Hydration produces an increase in overall reflectance with gradual development of water and hydroxyl absorptions at 1.4 μm and 1.9 μm. The oxidation of basaltic tephras can be observed spectrally through changes in the position and slope of the Fe3+ ‐ O2− charge transfer edge, inflections on that edge due to ferric oxide minerals and changes in the position and depth of the 1 μm iron crystal‐field band. Significantly in the tuffs examined, ferrous and ferric iron minerals produce one composite absorption feature rather than two resolvable bands. Different styles of alteration were noted between thinly bedded tuff ring deposits emplaced by high energy, largely dry, pyroclastic surge and massively bedded tuff cone deposits emplaced by wetter, lower energy pyroclastic flow. The former class of tephras become hydrated and only moderately oxidized with some limited development of dioctahedral smectite clay minerals and minimal palagonitization. The latter class of tephras are highly palagonitized which implies a high degree of hydration and oxidation. In fact, in the most highly altered tephras, all the Fe2+ that is initially in the volcanic glass is converted to Fe3+ within nanophase and bulk ferric oxide phases in the palagonite. There is also more extensive development in the tuff cone beds of zeolite and phyllosilicate minerals. The differences in reflectance spectra of altered basaltic tephras can be traced back to initial differences in the water/magma ratio extant at the volcanic vent; thus, Vis/IR spectrometry holds the potential to be used as a tool for investigations into the volcanic history and paleoclimate of volcanic terrains.