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WorldView-2 sensor for the detection of hematite and goethite in tropical soils
摘要： The objective of this work was to simulate the bands of the WorldView-2 sensor from laboratory specters, in order to study its potential to detect iron oxides, besides proposing a spectral index based on the depth of the spectral feature (RHGtPf). The iron index (IFe) and the hematite index (IHm), developed by Madeira Netto for bands of Landsat TM-5 sensor, were adjusted for WorldView-2 to test the potential of the new yellow band. The results showed that the yellow band degrades to 2% compared to the red one. This is due to fact that mineral quantification and identification are in the absorption feature, not in the reflectance one, and it is only improved in the visualization of color. A new spectral index, the RHGtPF, based on the depth feature with the continuum-removed spectra, was proposed, since the new bands of the WorldView-2 sensor – the coastal blue and yellow bands – allow a better individualization of the absorption features for goethite and hematite separately. The new index is statistically similar to the ratio Hm / Gt + Hm; however, it is not similar to the mineralogical relation obtained with Munsell colors.
关键词： mineralogical relation,spectral indices,remote sensing,spectral feature depth
更新于2025-09-04 15:30:14
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Multi-resolution Image Fusion in Remote Sensing () || Introduction
摘要： One of the major achievements of human beings is the ability to record observational data in the form of photographs, a science which dates back to 1826. Humans have always tried to reach greater heights (treetops, mountains, platforms, and so on) to observe phenomenon of interest, to decide on habitable places, farming and such other activities. Curiosity motivates human beings to take photographs of the earth from elevated platforms. In the initial days of photography, balloons, pigeons, and kites were used to capture such photographs. With the invention of the aircraft in 1903, the ?rst aerial photograph on a stable platform was made possible in 1909 [120]. In the 1960s and 1970s, the primary platform that was used to carry remote sensing instruments shifted from aircraft to satellites [120]. It was during this period that the word ‘remote sensing’ replaced the frequently used word ‘aerial photograph’. Satellites can cover wider land space than planes and can monitor areas on a regular basis.
关键词： image fusion,remote sensing,satellites,aerial photograph,hyper-spectral images,multi-spectral images,panchromatic image
更新于2025-09-04 15:30:14
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Multi-resolution Image Fusion in Remote Sensing () || Literature Review
摘要： In many remote sensing applications, the spatial information of a fused image is as important as the spectral information. In other words, it is necessary to have images that have the spectral resolution of multi-spectral (MS) images and the spatial resolution of a panchromatic image. A sensor with spatial and spectral resolution, at the same time is hardly feasible [139]. The coarse spatial resolution of MS images is the result of a trade off due to physical and technical constraints. The quantity of light energy which arrives onto the detector is proportional to the width of its spectral range and hence, is smaller in the MS sensor than in the Pan sensor. It is therefore necessary to increase the energy that impinges onto the MS detector to obtain acceptable signal-to-noise ratio. However, this is not possible due to technological limitations. Further, if the MS images had high spatial resolution, the amount of data to transmit would be larger. The difficulties in on-board storage and data transmission to the ground also restrict the spatial resolution of MS images. This makes the remote sensing satellite sensors acquire MS images with low spatial resolution and the Pan image with high spatial resolution. Thus, the MS images have high spectral but low spatial resolution and the Pan image has high spatial but low spectral resolution.
关键词： image fusion,remote sensing,spectral resolution,spatial resolution,multi-spectral images,panchromatic image,Pan-sharpening
更新于2025-09-04 15:30:14
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Spectral domain optical coherence tomography as an adjunctive tool for screening Beh?et uveitis
摘要： Background This study investigated the association of central macular thickness (CMT) and macular volume (MV) with severity of Behc?et uveitis in the absence of macular edema (ME). Methods This retrospective, interventional study included a total 131 treatment-na?ve Behc?et patients with varying degree of uveitis in the absence of ME. The mean CMT and MV were obtained by spectral domain optical coherence tomography (SD ODT). The patients were classified according to the anatomical classification of Behc?et uveitis. The main outcome measure was comparison of mean CMT and MV with the types of Behc?et uveitis. Results Sixty patients (45.8%) with no uveitis, 41 patients (31.3%) with anterior uveitis, 18 patients (13.7%) with posterior uveitis, and 12 patients (9.2%) with panuveitis. The mean CMT were 261.6±22.2 μm in no uveitis, 268.1±17.8 μm in anterior uveitis, 306.4±32.9 μm in posterior uveitis, and 300.4±44.0 μm in panuveitis (P < 0.001). The mean MV was 8.7±0.3 mm3 in those without uveitis, 8.8±0.3 mm3 in anterior uveitis, 9.9±1.1 mm3 in those with posterior uveitis, and 9.7±0.4 mm3 in panuveitis (P < 0.001). Types of Behc?et uveitis was the only significant factor correlated with the mean CMT (B = 18.170, β = 0.408, P < 0.001) and the mean MV (B = 0.328, β = 0.652, P < 0.001). Conclusions The mean CMT and MV were significantly thicker in the Behc?et uveitis with posterior involvement. SD OCT can be used for an adjunctive tool for screening Behc?et uveitis, especially for the presence of posterior involvement.
关键词： Behc?et uveitis,macular volume,posterior involvement,spectral domain optical coherence tomography,central macular thickness
更新于2025-09-04 15:30:14
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Using MOD09 Data to Produce a Natural-color Image from the Blue-lacked Multispectral Remote Sensing Data
摘要： Because of atmospheric effects, some satellite sensors cover only two visual spectral bands (green and red bands) in addition to bands in the near-infrared to thermal-infrared regions, and lack a blue band. As a result, a natural-color image cannot be obtained, as the blue band is necessary in combining red, green, and blue to produce natural color. This greatly affects the application of remote sensing in many areas such as virtual reality, terrain simulation, and visual interpretation. In this study, the MODIS land surface product (MOD09) was used as reference imagery from which to select pixel samples, and a non-linear regression analysis model—a back-propagation artificial neural network (BPN)—was used to fit the spectral reflectance relationship among the blue band and red, green, and near-infrared bands. Landsat TM/MSS, ZY1-02C and SPOT blue bands were then simulated with the trained fitting model, and a natural-color image was output. The experiment result shows that the MOD09 samples trained BPN model well simulated the blue band of a multispectral image and even more informative blue band, more importantly; it can eliminate the influence of the atmospheric for the blue band to some degree. With the simulated blue band, a more realistic and informative natural-color image was acquired.
关键词： MOD09,ZY1-02C,Spectral fitting,Natural-color,SPOT
更新于2025-09-04 15:30:14
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Characterisation and improvement of <i>j</i>(O<sup>1</sup>D) filter radiometers
摘要： Atmospheric O3 → O(1D) photolysis frequencies j (O1D) are crucial parameters for atmospheric photochemistry because of their importance for primary OH formation. Filter radiometers have been used for many years for in situ field measurements of j (O1D). Typically the relationship between the output of the instruments and j (O1D) is non-linear because of changes in the shape of the solar spectrum dependent on solar zenith angles and total ozone columns. These non-linearities can be compensated for by a correction method based on laboratory measurements of the spectral sensitivity of the filter radiometer and simulated solar actinic flux density spectra. Although this correction is routinely applied, the results of a previous field comparison study of several filter radiometers revealed that some corrections were inadequate. In this work the spectral characterisations of seven instruments were revised, and the correction procedures were updated and harmonised considering recent recommendations of absorption cross sections and quantum yields of the photolysis process O3 → O(1D). Previous inconsistencies were largely removed using these procedures. In addition, optical interference filters were replaced to improve the spectral properties of the instruments. Successive determinations of spectral sensitivities and field comparisons of the modified instruments with a spectroradiometer reference confirmed the improved performance. Overall, filter radiometers remain a low-maintenance alternative of spectroradiometers for accurate measurements of j (O1D) provided their spectral properties are known and potential drifts in sensitivities are monitored by regular calibrations with standard lamps or reference instruments.
关键词： atmospheric photochemistry,photolysis frequencies,spectral sensitivity,correction factors,filter radiometers
更新于2025-09-04 15:30:14
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The spectral signature of cloud spatial structure in shortwave irradiance
摘要： We found that cloud spatial structure manifests itself as spectral signature in shortwave irradiance fields – specifically in transmittance and net horizontal photon transport in the visible and near-ultraviolet wavelength range. In this paper, we demonstrate this through radiative transfer calculations with cloud imagery from a field experiment, and show that such three-dimensional effects may occur on scales up to 60 kilometers. Neglecting net horizontal photon transport leads to a transmittance bias on the order of ±12-19% even at the relatively coarse spatial resolution of 20 kilometers, and of more than ±50% for 1 kilometer. This poses a problem for radiative energy budget estimates from space because the bias for any pixel depends on its spatial context in a non-trivial way. The key for solving this problem may lie in the spectral dimension, since we found a robust correlation between the magnitude of net horizontal photon transport (H) and its spectral dependence (slope). It is scale-invariant and holds for the entire pixel population of a domain. This was at first surprising given the large degree of spatial inhomogeneity, but seems to be valid for any cloud field. We prove that the underlying physical mechanism for this phenomenon is molecular scattering in conjunction with cloud inhomogeneity. On this basis, we developed a simple parameterization through a single parameter ??, which quantifies the characteristic spectral signature of spatial heterogeneities. In a companion paper, we will show that it is accompanied by spectral radiance perturbations, which can be detected from multi-spectral imagers and may be translated into bias reductions for cloud radiative effect estimates in the future.
关键词： cloud spatial structure,molecular scattering,shortwave irradiance,spectral signature,radiative transfer,cloud radiative effect,horizontal photon transport
更新于2025-09-04 15:30:14
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Spectral analysis of atmospheric composition: application to surface ozone model-measurement comparisons
摘要： Models of atmospheric composition play an essential role in our scientific understanding of atmospheric processes and in providing policy strategies to deal with societally relevant problems such as climate change, air quality and ecosystem degradation. The fidelity of these models needs to be assessed against observations to ensure that errors in model formulations are found and that model limitations are understood. A range of approaches are necessary for these comparisons. Here, we apply a spectral analysis methodology for this comparison. We use the Lomb-Scargle Periodogram, a method similar to a Fourier transform, but better suited to dealing with the gapped data sets typical of observational data. We apply this methodology to long-term hourly ozone observations and the equivalent model (GEOS-Chem) output. We show that the spectrally transformed observational data shows a distinct power spectrum with regimes indicative of meteorological processes (weather, macroweather) and specific peaks observed at the daily and annual timescales together with corresponding harmonic peaks at half, third etc. of these frequencies. Model output shows corresponding features. A comparison between the amplitude and phase of these peaks introduces a new comparison methodology between model and measurements. We focus on the amplitude and phase of diurnal and seasonal cycles and present observational/model comparisons and discuss model performance. We find large biases notably for the seasonal cycle in the mid-latitude northern hemisphere where the amplitudes are generally overestimated by up to 16 ppb, and phases are too late on the order of 1-5 months. This spectral methodology can be applied to a range of model-measurement applications and is highly suitable for Multimodel Intercomparison Projects (MIPs).
关键词： Lomb-Scargle Periodogram,ozone,spectral analysis,GEOS-Chem,model-measurement comparisons,atmospheric composition
更新于2025-09-04 15:30:14
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Mapping terrestrial oil spill impact using machine learning random forest and Landsat 8 OLI imagery: a case site within the Niger Delta region of Nigeria
摘要： Terrestrial oil pollution is one of the major causes of ecological damage within the Niger Delta region of Nigeria and has caused a considerable loss of mangroves and arable croplands since the discovery of crude oil in 1956. The exact extent of landcover loss due to oil pollution remains uncertain due to the variability in factors such as volume and size of the oil spills, the age of oil, and its effects on the different vegetation types. Here, the feasibility of identifying oil-impacted land in the Niger Delta region of Nigeria with a machine learning random forest classifier using Landsat 8 (OLI spectral bands) and Vegetation Health Indices is explored. Oil spill incident data for the years 2015 and 2016 were obtained from published records of the National Oil Spill Detection and Response Agency and Shell Petroleum Development Corporation. Various health indices and spectral wavelengths from visible, near-infrared, and shortwave infrared bands were fused and classified using the machine learning random forest classifier to distinguish between oil-free and oil spill–impacted landcover. This provided the basis for the identification of the best variables for discriminating oil polluted from unpolluted land. Results showed that better results for discriminating oil-free and oil polluted landcovers were obtained when individual landcover types were classified separately as opposed to when the full study area image including all landcover types was classified at once. Similarly, the results also showed that biomass density plays a significant role in the characterization and classification of oil contaminated and oil-free pixels as tree cover areas showed higher classification accuracy compared to cropland and grassland.
关键词： Spectral bands,Vegetation health indices,Variable importance,Random forest,Oil spill,Landcover
更新于2025-09-04 15:30:14
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Quantum communication improved by spectral entanglement and supplementary chromatic dispersion
摘要： Implementations of many quantum communication protocols require sources of photon pairs. However, optimization of the properties of these photons for speci?c applications is an open problem. We theoretically demonstrate the possibility of extending the maximal distance of secure quantum communication when a photon pair source and standard ?bers are used in a scenario where Alice and Bob do not share a global time reference. It is done by manipulating the spectral correlation within a photon pair and by optimizing chromatic dispersion in transmission links. Contrary to typical expectations, we show that in some situations the secure communication distance can be increased by introducing some extra dispersion.
关键词： quantum communication,secure communication distance,chromatic dispersion,photon pairs,spectral entanglement
更新于2025-09-04 15:30:14