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Advancing the PROSPECT-5 Model to Simulate the Spectral Reflectance of Copper-Stressed Leaves
摘要： This paper proposes a modified model based on the PROSPECT-5 model to simulate the spectral reflectance of copper-stressed leaves. Compared with PROSPECT-5, the modified model adds the copper content of leaves as one of input variables, and the specific absorption coefficient related to copper (Kcu) was estimated and fixed in the modified model. The specific absorption coefficients of other biochemical components (chlorophyll, carotenoid, water, dry matter) were the same as those in PROSPECT-5. Firstly, based on PROSPECT-5, we estimated the leaf structure parameters (N), using biochemical contents (chlorophyll, carotenoid, water, and dry matter) and the spectra of all the copper-stressed leaves (samples). Secondly, the specific absorption coefficient related to copper (Kcu) was estimated by fitting the simulated spectra to the measured spectra using 22 samples. Thirdly, other samples were used to verify the effectiveness of the modified model. The spectra with the new model are closer to the measured spectra when compared to that with PROSPECT-5. Moreover, for all the datasets used for validation and calibration, the root mean square errors (RMSEs) from the new model are less than that from PROSPECT-5. The differences between simulated reflectance and measured reflectance at key wavelengths with the new model are nearer to zero than those with the PROSPECT-5 model. This study demonstrated that the modified model could get more accurate spectral reflectance from copper-stressed leaves when compared with PROSPECT-5, and would provide theoretical support for monitoring the vegetation stressed by copper using remote sensing.
关键词： vegetation remote sensing,leaf,PROSPECT,reflectance model,copper,spectra
更新于2025-09-23 15:23:52
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Detection of peanut leaf spots disease using canopy hyperspectral reflectance
摘要： Leaf spot is one of the most destructive diseases, which has a significant impact on the peanut production. Detecting leaf spot via spectral measurement and analysis is a possible alternative to traditional methods in detecting the spatial distribution of this disease. In this study, we identified sensitive bands and derived hyperspectral vegetation index specific to leaf spot detection. Hyperspectral canopy reflectance spectra of peanut cultivars susceptibilities to leaf spot were measured at two experimental sites in 2017. The normalized difference spectral index (NDSI) was derived based on their correlation with disease index (DI) in the leaf spectrum between 325 nm and 1075 nm. The results showed that canopy spectral reflectance decreased significantly in the near-infrared regions (NIR) as DI increased (r < -0.90). The spectral index for detecting leaf spot in peanut were LSI: (NDSI (R938, R761)) with R2 values of up to 0.68 for the regression model. The high fit between the observed and estimated values indicates that the DI detecting model based on the index could be used in peanut leaf spot detection in the absence of other stresses causing unhealthy symptoms. The results of this study show that it will provide a reliable, effective and accurate method for detecting leaf spot diseases in peanut through the analysis of hyperspectral data in the future.
关键词： Vegetation index,Disease index,Arachis hypogaea L.,Canopy hyperspectral reflectance
更新于2025-09-23 15:23:52
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Monte Carlo based model for diffuse reflectance from turbid media for the diagnosis of epithelial dysplasia
摘要： Diffuse reflectance from biological tissue has been widely used in diagnostic oncology for characterizing biochemical and morphological changes in epithelial tissue. However, computational complexity and time consumption involved in the extraction of absorption and scattering properties of tissues from diffuse reflectance reduce its potentiality for the effective diagnosis in a clinical setup. In this regard, a simple and accurate empirical equation for diffuse reflectance from a turbid medium was developed. A diffuse reflectance lookup table was generated using Monte Carlo simulations of all the optical properties typical of soft tissues in the visible and near infrared region of the spectrum for a semi-infinite medium. The generated lookup table was used to extract an empirical equation for diffuse reflectance using the surface fitting method. The proposed equation was tested with simulations and tissue phantom validation studies. The accuracy of the proposed empirical equation is tenfold higher than the diffusion approximation method. The uniqueness of the present method lies in its reliability even at extremities.
关键词： turbid medium,empirical model,Monte Carlo,epithelial dysplasia,diffuse reflectance
更新于2025-09-23 15:23:52
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Promising red emission from functionalized Polypyrrole/CaTiO3:Eu3+ nano-composites for photonic applications
摘要： CaTiO3:Eu3+ luminescent nanoparticles (NPs) and Ppy/CaTiO3:Eu3+ nanocomposites (NCs) are synthesized via combustion and solution casting techniques respectively and their structural and optical properties are investigated. The powder X-ray diffraction patterns of the as-formed products show single orthorhombic phase. The crystallite size measurement is assessed utilizing Scherrer's technique and observed to be in the range of 40–45 nm. The impact of Eu3+ ions on luminescence properties of the produced nanophosphors is examined the outcomes are given in detail. The phosphors displayed splendid red emission at 398 nm excitation. The emission peaks observed at 540, 593, 615, 653, 696 and 706 nm (5D0→7Fj = 0, 1, 2, 3, 4, 5) are assigned to Eu3+ ions transitions. The electronic transition equivalent to 5D0→7F2 (615 nm) is robust than the magnetic dipole transition 5D0→7F1 of Eu3+ ions (596 nm). The CIE chromaticity co-ordinates are ascertained from emanation spectra, the obtained values are very close to NTSC standard value of red emission. Hence, the present phosphors are exceedingly valuable for display applications. The obtained results demonstrate that Ppy-assisted solution casting is an effective methodology for the synthesis of rare-earth doped CaTiO3:Eu3+ nanocomposites (NCs).
关键词： Diffuse reflectance,Microbial activity,Nanocomposites,Color diagrams,Polypyrrole
更新于2025-09-23 15:23:52
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A spectroscopic method for quick evaluation of tint strength and tint tone of titania (rutile) pigment and factors affecting them
摘要： Titanium dioxide (TiO2) manufacturing industries measure optical properties such as brightness, colour, tint strength, tint tone, gloss, scatter coefficient, and others to ensure the quality of the product. Product characterization and process control generally focus on the optical properties, which determine its quality. In this work, titania rutile pigment with varying tint strength and tint tone is analyzed and a correlation is established between particle size and the optical properties such as tint strength and tint tone. It is observed that optical properties of titania pigment depends on the particle size as well as particle size distribution. A relatively faster evaluation of tint strength and tint tone can be made using the reflectance and particle size measurements. Analytical samples were prepared by ultrasonic dispersion of pigment in water containing calgon as dispersing agent. To verify the accuracy of the method, pigment tint strength and tint tone obtained from this study are compared with those resulting from traditional analysis. The results showed that the new method is viable.
关键词： optical properties,tint strength,reflectance,titania pigment,tint tone
更新于2025-09-23 15:23:52
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Reflectance confocal microscopy margin mapping and monitoring of an amelanotic melanoma <i>in situ</i> of the ear
摘要： In situ amelanotic melanoma represents a diagnostic challenge for clinicians. Poor demarcation of these lesions often results in repeated therapeutic intervention until appropriate clearance has been achieved. Reflectance confocal microscopy (RCM) is a noninvasive bedside imaging modality which allows real-time visualisation, to a near-histological level, of the epidermis and reticular dermis. We present a case of an amelanotic melanoma in situ in which reflectance confocal microscopy margin mapping allowed for demarcation of the melanocytic proliferation and targeted therapeutic intervention with topical imiquimod. Reflectance confocal microscopy was further utilised for noninvasive assessment of therapeutic response.
关键词： margin mapping,reflectance confocal microscopy,amelanotic melanoma
更新于2025-09-23 15:23:52
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Synthesis and characterization of a series of new green solar heat-reflective pigments: Cr-doped BiPO4 and its effect on the aging resistance of PMMA (Poly(methyl methacrylate))
摘要： A series of new green Cr-doped BiPO4 materials were synthesized by hydrothermal method and first used as solar heat-reflective pigments. XRD, FTIR, FE-SEM and HR-TEM analyses confirm that the phase structure was transformed from low-temperature monoclinic phase (LTMP) to hydrated hexagonal phase (HP), the particle size decreased and the morphology changed from irregular prism-shaped to rod-shaped, which all attributed to the incorporation of Cr3+ ions. Moreover, the valance of chromium ions was also confirmed by XPS. Color and ultraviolet-visible-near-infrared (UV–Vis–NIR) analysis indicate that different hues of green were obtained in these solid solutions and they possessed high NIR reflectance (> 83%) and solar reflectance (> 86%) in total NIR region. Meanwhile, the reason of decrease in NIR reflectance of doped samples was also analyzed, which mainly due to the decrease of free carrier concentration. TG-DTA and corrosion resistance tests prove that these pigments have excellent thermal and chemical stability. Compared with pure PMMA and the existing reports on pigmented PMMA, the NIR reflectance of PMMA pigmented with Cr-doped BiPO4 pigments have been greatly improved and have good coloring performance. The NIR solar reflectance of PMMA colored with Bi0.85Cr0.15PO4 in shortwave NIR region reaches up to 77.83%, an increase of nearly 52%. Heat aging test shows that Cr-doped BiPO4 pigments significantly improve the aging resistance of PMMA. In conclusion, these pigments have potential to become plastic colorants to increase the NIR reflectance and aging resistance of plastics.
关键词： Green pigments,Cr-doped BiPO4,Aging resistance,NIR reflectance,PMMA
更新于2025-09-23 15:23:52
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Resonance reflection of light by ordered silicon nanopillar arrays with the vertical p-n junction
摘要： Silicon nanopillar (Si NP) arrays with the axial p-n junction were formed and investigated. A method to fabricate Si NP ordered arrays by means of electron beam lithography using the negative electron resist and reactive ion etching is presented. The effect of strong resonance light scattering – change of the color of separate Si NPs - was demonstrated. One or several minima were registered in the measured reflection spectra. Thereat, the position of reflection minimum was changed with a change in Si NP diameter. A shift of the minimum position towards the longer wavelength spectral region with an increase in Si NP diameter was observed. A shift of the position of minima to the shorter wavelength spectral region with a decrease in Si NP pitch in microarrays with the same Si NP diameter was observed. The quantitative divergence in the position of reflection minima in Si NPs with calculated dependencies for Mie resonances was found. High photosensitivity of Si NP arrays with axial p-n junction to visible and near IR light was discovered. So, these structures may be used for selective photonic sensors.
关键词： reflectance spectra,silicon nanopillars,electrophysical properties,reactive ion etching,electron beam lithography
更新于2025-09-23 15:23:52
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Large-Area Gap Filling of Landsat Reflectance Time Series by Spectral-Angle-Mapper Based Spatio-Temporal Similarity (SAMSTS)
摘要： Landsat time series commonly contain missing observations, i.e., gaps, due to the orbit and sensing geometry, data acquisition strategy, and cloud contamination. A spectral-angle-mapper (SAM) based spatio-temporal similarity (SAMSTS) gap-filling algorithm is presented that is designed to fill small and large area gaps in Landsat data, using one year or less of data and without using other satellite data. Each gap pixel is filled by an alternative similar pixel that is located in a non-missing region of the image. The alternative similar pixel locations are identified by comparison of reflectance time series using a SAM metric revised to be adaptive to missing observations. A time series segmentation-and-clustering approach is used to increase the search efficiency. The SAMSTS algorithm is demonstrated using six months of Landsat 8 Operational Land Imager (OLI) reflectance time series over three 150 × 150 km (5000 × 5000 30 m pixels) areas in California, Minnesota and Kansas. The three areas contain different land cover types, especially crops that have different phenology and abrupt changes due to agricultural harvesting, which make gap filling challenging. Fillings on simulated gaps, which are equivalent to 36% of 5000 × 5000 images in each test area, are presented. The gap filling accuracy is assessed quantitatively, and the SAMSTS algorithm is shown to perform better than the simple closest temporal pixel substitution gap filling approach and the sinusoidal harmonic model-based gap filling approach. The SAMSTS algorithm provides gap-filled data with five-band reflective-wavelength root-mean-square differences less the 0.02, which is comparable to the OLI reflectance calibration accuracy.
关键词： Landsat,reflectance,time series,spectral angle mapper,gap filling
更新于2025-09-23 15:23:52
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A Novel Tilt Correction Technique for Irradiance Sensors and Spectrometers On-Board Unmanned Aerial Vehicles
摘要： In unstable atmospheric conditions, using on-board irradiance sensors is one of the only robust methods to convert unmanned aerial vehicle (UAV)-based optical remote sensing data to reflectance factors. Normally, such sensors experience significant errors due to tilting of the UAV, if not installed on a stabilizing gimbal. Unfortunately, such gimbals of sufficient accuracy are heavy, cumbersome, and cannot be installed on all UAV platforms. In this paper, we present the FGI Aerial Image Reference System (FGI AIRS) developed at the Finnish Geospatial Research Institute (FGI) and a novel method for optical and mathematical tilt correction of the irradiance measurements. The FGI AIRS is a sensor unit for UAVs that provides the irradiance spectrum, Real Time Kinematic (RTK)/Post Processed Kinematic (PPK) GNSS position, and orientation for the attached cameras. The FGI AIRS processes the reference data in real time for each acquired image and can send it to an on-board or on-cloud processing unit. The novel correction method is based on three RGB photodiodes that are tilted 10° in opposite directions. These photodiodes sample the irradiance readings at different sensor tilts, from which reading of a virtual horizontal irradiance sensor is calculated. The FGI AIRS was tested, and the method was shown to allow on-board measurement of irradiance at an accuracy better than ±0.8% at UAV tilts up to 10° and ±1.2% at tilts up to 15°. In addition, the accuracy of FGI AIRS to produce reflectance-factor-calibrated aerial images was compared against the traditional methods. In the unstable weather conditions of the experiment, both the FGI AIRS and the on-ground spectrometer were able to produce radiometrically accurate and visually pleasing orthomosaics, while the reflectance reference panels and the on-board irradiance sensor without stabilization or tilt correction both failed to do so. The authors recommend the implementation of the proposed tilt correction method in all future UAV irradiance sensors if they are not to be installed on a gimbal.
关键词： unmanned aerial vehicle,UAV,irradiance,reflectance factor,tilt stabilization,drone
更新于2025-09-23 15:23:52