Spectral Comparison Research Articles

The Steklov spectrum and coarse discretizations of manifolds with boundary

We consider the class of compact n-dimensional Riemannian manifolds with cylindrical boundary, Ricci curvature bounded below by a given constant and injectivity radius bounded below by a positive constant, away from the boundary. For a manifold M of this class, we introduce a notion of discretization, leading to a graph with boundary which is roughly isometric to M, with constants depending only on the dimension and bounds on curvature and injectivity radius. In this context, we prove a uniform spectral comparison inequality between the Steklov eigenvalues of the manifold M and those of its discretization. Some applications to the construction of sequences of surfaces with boundary of fixed length and with arbitrarily large Steklov spectral gap are given. In particular, we obtain such a sequence for surfaces with connected boundary. The applications are based on the construction of graph-like surfaces which are obtained from sequences of graphs with good expansion properties.

Matrix-assisted laser desorption/ionization tandem mass spectrometry for identification of organic tattoo pigments in inks and tissue samples.

With regard to the increasing number of tattooed people, legal regulations for tattoo inks were implemented across Europe-aiming for higher consumer safety. To control the laws' abidance, analytical methods are needed to identify banned ingredients from the given negative lists. Since specific organic pigments are often associated with tattoo side effects, their identification in tattoo inks as well as in biological samples is of great importance. Particularly, poorly soluble organic pigments are challenging to detect. In the past, matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) was reported as a promising tool for organic pigment identification. Here, we present a MALDI tandem mass spectrometry (MS/MS) approach to increase identification specificity and sensitivity in the process based on pigment fragment ions which is of special importance in tissue samples. For further verification of pigment identities, alkali metal cation attachment was used. Sample preparation was optimized and included mechanical disruption followed by the application as dried droplets with the matrices α-cyano-4-phenylcinnamic acid and sinapinic acid as well as ethanol. Pigments were identified by spectral comparison to reference libraries containing 40 pigments and following a decision tree. Additionally, successful pigment identification in biological samples was carried out. The implemented automated MALDI-MS and -MS/MS acquisitions make the hereby proposed pigment identification suitable for routine application.

Antimutagenic activity of compounds isolated from Ajuga bracteosa Wall ex. Benth against EMS induced mutagenicity in mice.

Ajuga bracteosa Wall ex. Benth. (Lamiaceae) has been reported to possess many biological activities including antibacterial, antifungal, antispasmodic and antioxidant activity but there is no report as such on its mutagenic and/or anti-mutagenic activity. The aim of the present study was to isolate compounds from the methanol extract of the aerial parts of Ajuga bracteosa and determine their anti-mutagenic activity against the mutagen, EMS in animal model mice. The study was undertaken in order to corroborate the traditional use of the plant Ajuga bracteosa. The compounds were isolated from the methanol extract of the aerial parts of Ajuga bracteosa using silica gel column chromatography. Structural elucidation of the isolated compounds was done using spectral data analysis and comparison with literature. High performance liquid chromatography (HPLC) was used for the qualitative and quantitative determination of the isolated compounds in the crude methanol extract. The isolated compounds and standard drug were evaluated in vivo for antimutagenic activity against EMS induced mutagenicity taking mice as model organism by micronucleus and chromosomal aberration tests. Four major compounds were identified as 1) 14, 15-dihydroajugapitin 2) β- Sitosterol 3) Stigmasterol and 4) 8-O-acetylharpagide. A quick and sensitive HPLC method was developed for qualitative and quantitative determination of three isolated marker compounds from Ajuga bracteosa. 14, 15-dihydroajugapitin reduced the micronuclei by 85.10%, followed by β- Sitosterol (72.3%) while as 8-O-acetylharpagide reduced the micronuclei by 46%. It is therefore evident from the present study that the plant contains rich source of anticancer and antimutagenic drugs.

Isolation and Identification of Compounds from the Leaf Extract of Melaleuca alternifolia

Introduction: Melaleuca alternifolia also known as Tea tree oil belonging to family Myrtaceae. This plant has diverse and therapeutic uses in traditional herbal medicine for treating Skin care, First Aid, Household Cleaning, Hair care, Aromatherapy, Feminine care, Chronic illness, and Dental care in Australia. Method: The methanolic extract of Melaleuca alternifolia family Myrtaceae was subjected for Soxhlet extraction in round bottomed flask with petroleum ether. The petroleum ether extracted leaf powder was dried and once again subjected to Soxhlet extraction successively with different solvents viz, chloroform, ethyl acetate and methanol. Result: The IR spectra showed characteristic absorption bands at 3421 cm-1 indicating the presence of a OH group, at 1691cm-1 for C=O group, 2848 cm-1. The 1HNMR spectra showed a triplet signal at δ 10.44, 9.48, 13.21 showing the presence of OH group and Carboxylic acid. The 13C NMR spectra showed signals at δ 16.28 for a methyl carbon, δ 29.89 for a methylene carbon, The ESI-negative mode mass spectrum showed pseudo molecular ions at m/z 515 for [M+] ion. Conclusion: Based on spectral analysis and comparison of the spectral data with literature values, the compounds were identified as 3,3’dimethylellagic acid and its aglycone portion with some little impurity.

Chemometric Methods to Quantify 1D and 2D NMR Spectral Differences Among Similar Protein Therapeutics.

NMR spectroscopy is an emerging analytical tool for measuring complex drug product qualities, e.g., protein higher order structure (HOS) or heparin chemical composition. Most drug NMR spectra have been visually analyzed; however, NMR spectra are inherently quantitative and multivariate and thus suitable for chemometric analysis. Therefore, quantitative measurements derived from chemometric comparisons between spectra could be a key step in establishing acceptance criteria for a new generic drug or a new batch after manufacture change. To measure the capability of chemometric methods to differentiate comparator NMR spectra, we calculated inter-spectra difference metrics on 1D/2D spectra of two insulin drugs, Humulin R® and Novolin R®, from different manufacturers. Both insulin drugs have an identical drug substance but differ in formulation. Chemometric methods (i.e., principal component analysis (PCA), 3-way Tucker3 or graph invariant (GI)) were performed to calculate Mahalanobis distance (D M) between the two brands (inter-brand) and distance ratio (D R) among the different lots (intra-brand). The PCA on 1D inter-brand spectral comparison yielded a D M value of 213. In comparing 2D spectra, the Tucker3 analysis yielded the highest differentiability value (D M=305) in the comparisons made followed by PCA (D M=255) then the GI method (D M=40). In conclusion, drug quality comparisons among different lots might benefit from PCA on 1D spectra for rapidly comparing many samples, while higher resolution but more time-consuming 2D-NMR-data-based comparisons using Tucker3 analysis or PCA provide a greater level of assurance for drug structural similarity evaluation between drug brands.

Spectral characterization and comparison of humic acids isolated from some European lignites

Humic acids isolated from seven lignite samples from six European coal basins were characterized using spectral methods and elemental analysis and compared with each other. X-ray photoelectron spectroscopy and fluorescence spectrometry are not commonly used for the investigation of lignite humic acids, although they may provide relevant information. Comparison of the examined lignite humic acids shows that they are very similar to each other in chemical nature regarding the at least degree of aromaticity, molecular weight, and the distribution of functional groups. Fluorophores of lignite humic acids lie within the A region with typical maxima centred in the range 255–265/460–510 nm. EEM spectra have the character of fingerprints for humic acids, and lignites (as the starting material). In this work, the capacity of lignite as a parent source of humic acids for agricultural applications is appreciated mainly on the base of extractability and ash content.

A colorimetric Pb2+ chemosensor: Rapid naked-eye detection, high selectivity, theoretical insights, and applications

A novel colorimetric chemosensor (MRN1) was designed and synthesized by incorporating the azobenzene disperse dye-based signalling unit and tridentate chelating moiety into a single molecule. MRN1 showed a selective and sensitive colorimetric sensing ability for Pb2+ ion by changing color from light yellow to magenta in an aqueous media. Detailed spectral investigations, mass spectrometry, and comparison (MRN2) studies provided corroborative evidence in support of 1: 1 association between MRN1 and Pb2+. The drastically red-shifted absorption spectrum of MRN1 upon addition of Pb2+ was proposed to be metal-to-ligand charge-transfer (MLCT) and intramolecular charge transfer (ICT) through the experimental results and density functional theory (DFT/TDDFT) calculations. Using this methodology, MRN1 could be used as a practical and visible test strip for Pb2+. MRN1 could also be used as a preliminary sensor for monitoring Pb2+ adsorbed in living Daphnia magna using an optical microscope.

Role of dynamical injection locking and characteristic pulse events for low frequency fluctuations in semiconductor lasers.

We investigate the dynamics of semiconductor lasers subject to time-delayed optical feedback from the perspective of dynamical self-injection locking. Based on the Lang-Kobayashi model, we perform an analysis of the well-known Low Frequency Fluctuations (LFFs) in the frequency-intensity plane. Moreover, we investigate a recently found dynamical regime of fragmented LFFs by means of a locking-range analysis, spectral comparison and precursor pulse identification. We show that LFF dynamics can be explained by dynamical optical injection locking due to the delayed optical feedback. Moreover, the fragmented LFFs occur due to a re-injection locking induced by a particular optical pulse structure in the chaotic feedback dynamics. This is corroborated by experiments with a semiconductor laser experiencing delayed feedback from an optical fiber loop. The dynamical nature of the feedback injection results in an eventual loss, but also possible regaining, of the locking, explaining the recently observed phenomenon of fragmented LFFs.

Anti-Inflammatory Lobane and Prenyleudesmane Diterpenoids from the Soft Coral Lobophytum varium.

New lobane-based diterpenoids lobovarols A–D (1–4) and a prenyleudesmane-type diterpenoid lobovarol E (5) along with seven known related diterpenoids (6–12) were isolated from the ethyl acetate extract of a Taiwanese soft coral Lobophytum varium. Their structures were identified on the basis of multiple spectroscopic analyses and spectral comparison. The absolute configuration at C-16 of the known compound 11 is reported herein for the first time. The anti-inflammatory activities of compounds 1–12 were assessed by measuring their inhibitory effect on N-formyl-methionyl-leucyl-phenyl-alanine/cytochalasin B (fMLP/CB)-induced superoxide anion generation and elastase release in human neutrophils. Metabolites 2, 5, and 11 were found to show moderate inhibitory activity on the generation of superoxide anion, while compounds 5, 8, 11, and 12 could effectively suppress elastase release in fMLP/CB-stimulated human neutrophil cells at 10 μM. All of the isolated diterpenoids did not exhibit cytotoxic activity (IC50 > 50 μM) towards a limited panel of cancer cell lines.

Identification of drivers for the metamorphic transition of HIV-1 reverse transcriptase.

Recent structural characterizations of the p51 and p66 monomers have established an important starting point for understanding the maturation pathway of the human immunodeficiency virus (HIV)-1 reverse transcriptase p66/p51 heterodimer. This process requires a metamorphic transition of the polymerase domain leading to formation of a p66/p66' homodimer that exists as a structural heterodimer. To better understand the drivers for this metamorphic transition, we have performed NMR studies of 15N-labeled RT216 - a construct that includes the fingers and most of the palm domains. These studies are consistent with the conclusion that the p66 monomer exists as a spring-loaded complex. Initial dissociation of the fingers/palm : connection complex allows the fingers/palm to adopt an alternate, more stable structure, reducing the rate of reassociation and facilitating subsequent maturation steps. One of the drivers for an initial extension of the fingers/palm domains is identified as a straightening of helix E relative to its conformation in the monomer by eliminating a bend of ∼50° near residue Phe160. NMR and circular dichroism data also are consistent with the conclusion that a hydrophobic surface of palm domain that becomes exposed after the initial dissociation, as well as the intrinsic conformational preferences of the palm domain C-terminal segment, facilitates the formation of the β-sheet structure that is unique to the active polymerase subunit. Spectral comparisons based on 15N-labeled constructs are all consistent with previous structural conclusions based on studies of 13C-methyl-labeled constructs.

Two new sesquarterpenoids from the bark of Cryptomeria japonica

Two new sesquarterpenoids, i.e. ferrugicadinol A (1) and ferrugicryptomeridiol (3), and one known sesquarterpenoid, ferrugicadinol (2) were isolated from the bark of Cryptomeria japonica D. Don. Their structures were identified by extensive spectral analysis and comparison with the data of known analogues.

An extensive VLT/X-shooter library of photospheric templates of pre-main sequence stars

Studies of the formation and evolution of young stars and their disks rely on the knowledge of the stellar parameters of the young stars. The derivation of these parameters is commonly based on comparison with photospheric template spectra. Furthermore, chromospheric emission in young active stars impacts the measurement of mass accretion rates, a key quantity to study disk evolution. Here we derive stellar properties of low-mass pre-main sequence stars without disks, which represent ideal photospheric templates for studies of young stars. We also use these spectra to constrain the impact of chromospheric emission on the measurements of mass accretion rates. The spectra in reduced, flux-calibrated, and corrected for telluric absorption form are made available to the community. We derive the spectral type for our targets by analyzing the photospheric molecular features present in their VLT/X-Shooter spectra by means of spectral indices and comparison of the relative strength of photospheric absorption features. We also measure effective temperature, gravity, projected rotational velocity, and radial velocity from our spectra by fitting them with synthetic spectra with the ROTFIT tool. The targets have negligible extinction and spectral type from G5 to M8. We perform synthetic photometry on the spectra to derive the typical colors of young stars in different filters. We measure the luminosity of the emission lines present in the spectra and estimate the noise due to chromospheric emission in the measurements of accretion luminosity in accreting stars. We provide a calibration of the photospheric colors of young PMS stars as a function of their spectral type in a set of standard broad-band optical and near-infrared filters. For stars with masses of ~ 1.5Msun and ages of ~1-5 Myr, the chromospheric noise converts to a limit of measurable mass accretion rates of ~ 3x10^-10 Msun/yr.

Validation and Peak Purity Assessment of RP-HPLC Method for Simultaneous Estimation of Amitriptyline HCl, Chlordiazepoxide and Comparison with Spectrophotometry

Purpose : The study was performed with the aim to design a Simple, precise and economical RP-HPLC method have been developed for simultaneous estimation of amitriptyline HCl and chlordiazepoxide in pharmaceutical formulation. Approach : RP-HPLC was developed using WATERS C18 250 mm × 4.6 mm (5 μm) column, utilizing a mobile phase of methanol: acetonitrile: 0.2 M orthophosphoric acid, pH 4.5 (adjusted with triethylamine) 56:24:20 ml (with a flow rate of 1ml/min) and U.V detection was carried out at 240nm. Optimization of this method was carried out as a function of mobile phase composition, pH and flow rate. Peak purity was assessed by spectral comparison method. Findings : RP-HPLC method shows linearity in the range of for 0.05-1.6 μg/ml and 0.01-0.32μg/ml amitriptyline HCl and chlordiazepoxide respectively. The LOD and LOQ values for amitriptyline HCl were 0.0250μg/ml and 0.0759 μg/ml and 0.0045 μg/ml and 0.0135 μg/ml for chlordiazepoxide. The results of % purity was found to be 99.97 ± 0.58 % w/w and 99.29 ± 0.59 % w/w for HPLC method and 98.87 ± 0.03 % w/w and 98.81 ± 1.04 % w/w for first derivative spectrophotometric method for amitriptyline HCl and chlordiazepoxide respectively. Conclusion : Results of descriptive statistics studies conclude that RP-HPLC method found to be more sensitive and convenient than first derivative spectrophotometric method.

Two emission turn-on optical chemosensors for cysteine detection using up-conversion nanocrystals as excitation host: Synthesis, characterization and performance

In this paper, two rhodamine derived chemosensors were synthesized for cysteine optical recognition. Up-conversion NaYF4:Yb3+/Er3+ nanocrystals were modified as hydrophilic ones by α-cyclodextrin (α-CD) and used as excitation host, hoping to improve photostability of our chemosensors. Spectral analysis and emission decay lifetime comparison suggested that there was an efficient energy transfer between our excitation host and chemosensors. Job’s plot analysis indicated a simple recognition mechanism with binding stoichiometry of 1:1. Chemosensor emission was increased with increasing cysteine concentration, showing good selectivity and linear sensing response. The correlation between sensing performance and chemosensor molecular structure was discussed. Sulfur substituent effect improved selectivity of chemosensors.

Isolation, purification and identification of antioxidants from Lepidium latifolium extracts

Antioxidant potencies of an ethanolic extract and its components from Lepidium latifolium were investigated. In this study, we found that the ethyl acetate soluble fraction of L. latifolium was a rich source of antioxidant, resulting from its high total phenolic content. To determine the antioxidant components of the ethyl acetate fraction, a bioassay-guided fractionation approach using 1,1-diphenyl-2-picrylhydrazyl, 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulfonate), and ferric reducing antioxidant power assays were conducted. Nine compounds were isolated and their structures were identified by MS and NMR spectral data and comparison to reported data. They are Quercetin-3-O-β-d-sophoroside-7-O-α-l-rhamnoside (1), Apetalumoside B6 (2), Kaempferol-3-O-β-d-glucopyranosyl-(1-2)-β-d-glucopyranoside-7-O-β-d-glucopyranoside (3), Kaempferol-7-O-α-l-rhamnopyranoside (4), Kaempferol-3-O-β-d-glucopyranoside-7-O-α-l-rhamnopyranoside (5), Kaempferol-3-O-(2-O-feruloyl-β-d-glucopyranosyl-(1-2)-β-d-glucopyranoside)-7-O-glucopyranoside (6), Kaempferol-3-O-β-d-sophoroside-7-O-α-l-rhamnoside (7), Kaempferol-3-O-robinoside-7-O-(2″″-(E)-feruloyl)-sophoroside (8), Quercetin-3-O-(2,6-di-O-β-d-glucopyranosyl)-β-d-glucopyranoside-7-O-α-l-rhamnopyranoside (9), compounds 1, 2, 4, and 8 had potent free radical scavenging activity. The IC50 values of these compounds were 9.8–12.3 and 7.4–31.4 μg/mL in DPPH and ABTS assays, respectively. The results indicate that L. latifolium is a potential natural source of antioxidants to treat several diseases related to oxidant by-products of human metabolism.

Improved spectral comparisons of paleoclimate models and observations via proxy system modeling: Implications for multi-decadal variability

The spectral characteristics of paleoclimate observations spanning the last millennium suggest the presence of significant low-frequency (multi-decadal to centennial scale) variability in the climate system. Since this low-frequency climate variability is critical for climate predictions on societally-relevant scales, it is essential to establish whether General Circulation models (GCMs) are able to simulate it faithfully. Recent studies find large discrepancies between models and paleoclimate data at low frequencies, prompting concerns surrounding the ability of GCMs to predict long-term, high-magnitude variability under greenhouse forcing (Laepple and Huybers, 2014a, 2014b). However, efforts to ground climate model simulations directly in paleoclimate observations are impeded by fundamental differences between models and the proxy data: proxy systems often record a multivariate and/or nonlinear response to climate, precluding a direct comparison to GCM output. In this paper we bridge this gap via a forward proxy modeling approach, coupled to an isotope-enabled GCM. This allows us to disentangle the various contributions to signals embedded in ice cores, speleothem calcite, coral aragonite, tree-ring width, and tree-ring cellulose. The paper addresses the following questions: (1) do forward-modeled “pseudoproxies” exhibit variability comparable to proxy data? (2) if not, which processes alter the shape of the spectrum of simulated climate variability, and are these processes broadly distinguishable from climate? We apply our method to representative case studies, and broaden these insights with an analysis of the PAGES2k database (PAGES2K Consortium, 2013). We find that current proxy system models (PSMs) can help resolve model-data discrepancies on interannual to decadal timescales, but cannot account for the mismatch in variance on multi-decadal to centennial timescales. We conclude that, specific to this set of PSMs and isotope-enabled model, the paleoclimate record may exhibit larger low-frequency variability than GCMs currently simulate, indicative of incomplete physics and/or forcings.

Translational Imaging Spectroscopy for Proximal Sensing.

Proximal sensing as the near field counterpart of remote sensing offers a broad variety of applications. Imaging spectroscopy in general and translational laboratory imaging spectroscopy in particular can be utilized for a variety of different research topics. Geoscientific applications require a precise pre-processing of hyperspectral data cubes to retrieve at-surface reflectance in order to conduct spectral feature-based comparison of unknown sample spectra to known library spectra. A new pre-processing chain called GeoMAP-Trans for at-surface reflectance retrieval is proposed here as an analogue to other algorithms published by the team of authors. It consists of a radiometric, a geometric and a spectral module. Each module consists of several processing steps that are described in detail. The processing chain was adapted to the broadly used HySPEX VNIR/SWIR imaging spectrometer system and tested using geological mineral samples. The performance was subjectively and objectively evaluated using standard artificial image quality metrics and comparative measurements of mineral and Lambertian diffuser standards with standard field and laboratory spectrometers. The proposed algorithm provides highly qualitative results, offers broad applicability through its generic design and might be the first one of its kind to be published. A high radiometric accuracy is achieved by the incorporation of the Reduction of Miscalibration Effects (ROME) framework. The geometric accuracy is higher than 1 μpixel. The critical spectral accuracy was relatively estimated by comparing spectra of standard field spectrometers to those from HySPEX for a Lambertian diffuser. The achieved spectral accuracy is better than 0.02% for the full spectrum and better than 98% for the absorption features. It was empirically shown that point and imaging spectrometers provide different results for non-Lambertian samples due to their different sensing principles, adjacency scattering impacts on the signal and anisotropic surface reflection properties.

Integrated active and semi-active control for seat suspension of a heavy duty vehicle

In this article, an integrated active and semi-active seat suspension for heavy duty vehicles is proposed, and its prototype is built; an integrated control algorithm applied measurable variables (suspension relative displacement and seat acceleration) is designed for the proposed seat prototype. In this seat prototype, an active actuator with low maximum force output (70 N), which is insufficient for an active seat suspension to control the resonance vibration, is applied together with a rotary magnetorheological damper. The magnetorheological damper can suppress the high vibration energy in resonance frequency, and then a small active force can further improve the seat suspension performance greatly. The suspension’s dynamic property is tested with a MTS system, and its model is identified based on the testing data. A modified on–off controller is applied for the rotary magnetorheological damper. A [Formula: see text] controller with the compensation of a disturbance observer is used for the active actuator. Considering the energy saving, the control strategy is designed as that only when the magnetorheological damper is in the off state (0 A current), the active actuator will have active force output, or the active actuator is off. Both simulation and experiment are implemented to verify the proposed seat suspension and controller. In the sinusoidal excitations experiment, the acceleration transmissibility of integrated control seat has lowest value in resonance frequency and frequencies above the resonance, when compared with power on (0.7 A current), power off (0 A current) and semi-active control seat. In the random vibration experiment, the root mean square acceleration of integrated control seat suspension has 47.7%, 33.1% and 26.5% reductions when compared with above-mentioned three kinds of seat suspension. The power spectral density comparison indicates that the integrated seat suspension will have good performance in practical application. The integrated active and semi-active seat suspension can fill energy consumption gap between active and semi-active control seat suspension.

Application of Abundance Map Reference Data for Spectral Unmixing

Reference data (“ground truth”) maps have traditionally been used to assess the accuracy of classification algorithms. These maps typically classify pixels or areas of imagery as belonging to a finite number of ground cover classes, but do not include sub-pixel abundance estimates; therefore, they are not sufficiently detailed to directly assess the performance of spectral unmixing algorithms. Our research aims to efficiently generate, validate, and apply abundance map reference data (AMRD) to airborne remote sensing scenes. Scene-wide AMRD for this study were generated using the remotely sensed reference data (RSRD) technique, which spatially aggregates classification or unmixing results from fine scale imagery (e.g., 1-m GSD) to co-located coarse scale imagery (e.g., 10-m GSD or larger). Validation of the accuracy of these methods was previously performed for generic 10 m × 10 m coarse scale imagery, resulting in AMRD with known accuracy. The purpose of this paper was to apply this previously validated AMRD to specific examples of airborne coarse scale imagery. Application of AMRD involved three main parts: (1) spatial alignment of coarse and fine scale imagery; (2) aggregation of fine scale abundances to produce coarse scale imagery specific AMRD; and (3) demonstration of comparisons between coarse scale unmixing abundances and AMRD. Spatial alignment was performed using our new scene-wide spectral comparison (SWSC) algorithm, which aligned imagery with accuracy approaching the distance of a single fine scale pixel. We compared simple rectangular aggregation to coarse sensor point-spread function (PSF) aggregation, and found that PSF returned lower error, but that rectangular aggregation more accurately estimated true AMRD at ground level. We demonstrated various metrics for comparing unmixing results to AMRD, including several new techniques which adjust for known error in the reference data itself. These metrics indicated that fully constrained linear unmixing of AVIRIS imagery across all three scenes returned an average error of 10.83% per class and pixel. Our reference data research has demonstrated a viable methodology to efficiently generate, validate, and apply AMRD to specific examples of airborne remote sensing imagery, thereby enabling direct quantitative assessment of spectral unmixing performance.

The role of atmospheric correction algorithms in the prediction of soil organic carbon from Hyperion data

ABSTRACTIn this study, the role of atmospheric correction algorithm in the prediction of soil organic carbon (SOC) from spaceborne hyperspectral sensor (Hyperion) visible near-infrared (vis-NIR, 400–2500 nm) data was analysed in fields located in two different geographical settings, viz. Karnataka in India and Narrabri in Australia. Atmospheric correction algorithms, (1) ATmospheric CORection (ATCOR), (2) Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH), (3) 6S, and (4) QUick Atmospheric Correction (QUAC), were employed for retrieving spectral reflectance from radiance image. The results showed that ATCOR corrected spectra coupled with partial least square regression prediction model, produced the best SOC prediction performances, irrespective of the study area. Comparing the results across study areas, Karnataka region gave lower prediction accuracy than Narrabri region. This may be explained due to difference in spatial arrangement of field conditions. A spectral similarity comparison of atmospherically corrected Hyperion spectra of soil samples with field-measured vis-NIR spectra was performed. Among the atmospheric correction algorithms, ATCOR corrected spectra found to capture the pattern in soil reflectance curve near 2200 nm. ATCOR’s finer spectral sampling distance in shortwave infrared wavelength region compared to other models may be the main reason for its better performance. This work would open up a great scope for accurate SOC mapping when future hyperspectral missions are realized.