Journal articles on the topic 'Reflectance'
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1
Ahmad, Noraini, Sabarinah Sh Ahmad, and Anuar Talib. "Surface Reflectance for Illuminance Level Control in Daylit Historical Museum Gallery under Tropical Sky Conditions." Advanced Materials Research 610-613 (December 2012): 2854–58. http://dx.doi.org/10.4028/www.scientific.net/amr.610-613.2854.
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Malaysia has tropical sky conditions, receiving plenty of natural light throughout the year. Natural light fluctuates greatly and it can be rather tricky to provide good distribution of daylight throughout an interior space and this prompts the need for strategic daylight control programme in a historic museum gallery. Surface reflectance is a significant design consideration, particularly with regards to how light is distributed throughout an interior space. Research on how the internal surfaces reflectances are controlled for long-term preservation of museum exhibits is still lacking for tropical skies conditions. The study aims to assess the internal surface reflectance contribution at a west facing daylit historical museum gallery through in-situ measurements and simulation model assessment. The results obtained in these experiments are visually compared with the existing surface reflectance values through simulation modelling. The results show new knowledge on light damage issues. The results also highlight daylighting distributions control and light exposure limits through realistic predictions’ images and reflectance’s alterations. The study confirms that surface reflectances can be a control mechanism for preventive conservation in the historical museum gallery.
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Hedley, John, Maryam Mirhakak, Adam Wentworth, and Heidi Dierssen. "Influence of Three-Dimensional Coral Structures on Hyperspectral Benthic Reflectance and Water-Leaving Reflectance." Applied Sciences 8, no. 12 (December 19, 2018): 2688. http://dx.doi.org/10.3390/app8122688.
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Shading and inter-reflections created by the three-dimensional coral canopy structure play an important role on benthic reflectance and its propagation above the water. Here, a plane parallel model was coupled with a three-dimensional radiative transfer canopy model, incorporating measured coral shapes and hyperspectral benthic reflectances, to investigate this question under different illumination and water column conditions. Results indicated that a Lambertian treatment of the bottom reflectance can be a reasonable assumption if a variable shading factor is included. Without flexibility in the shading treatment, nadir view bottom reflectances can vary by as much as ±20% (or ±9% in above-water remote sensing reflectance) under solar zenith angles (SZAs) up to 50°. Spectrally-independent shading factors are developed for benthic coral reflectance measurements based on the rugosity of the coral. In remote sensing applications, where the rugosity is unknown, a shading factor could be incorporated as an endmember for retrieval in the inversion scheme. In dense coral canopies in clear shallow waters, the benthos cannot always be treated as Lambertian, and for large solar-view angles the bi-directional reflectance distribution functions (BRDF) hotspot propagated to above water reflectances can create up to a 50% or more difference in water-leaving reflectances, and discrepancies of 20% even for nadir-view geometries.
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Lu, Xiaomei, Yongxiang Hu, Yuekui Yang, Mark Vaughan, Zhaoyan Liu, Sharon Rodier, William Hunt, Kathy Powell, Patricia Lucker, and Charles Trepte. "Laser pulse bidirectional reflectance from CALIPSO mission." Atmospheric Measurement Techniques 11, no. 6 (June 8, 2018): 3281–96. http://dx.doi.org/10.5194/amt-11-3281-2018.
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Abstract. This paper presents an innovative retrieval method that translates the CALIOP land surface laser pulse returns into the surface bidirectional reflectance. To better analyze the surface returns, the CALIOP receiver impulse response and the downlinked samples' distribution at 30 m vertical resolution are discussed. The saturated laser pulse magnitudes from snow and ice surfaces are recovered based on information extracted from the tail end of the surface signal. The retrieved snow surface bidirectional reflectance is compared with reflectance from both CALIOP cloud-covered regions and MODIS BRDF–albedo model parameters. In addition to the surface bidirectional reflectance, the column top-of-atmosphere bidirectional reflectances are calculated from the CALIOP lidar background data and compared with the bidirectional reflectances derived from WFC radiance measurements. The retrieved CALIOP surface bidirectional reflectance and column top-of-atmosphere bidirectional reflectance results provide unique information to complement existing MODIS standard data products and are expected to have valuable applications for modelers.
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Leckie, D. G., D. P. Ostaff, P. M. Teillet, and G. Fedosjevs. "Spectral Characteristics of Tree Components of Balsam Fir and Spruce Damaged by Spruce Budworm." Forest Science 35, no. 2 (June 1, 1989): 582–600. http://dx.doi.org/10.1093/forestscience/35.2.582.
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Abstract Spectral reflectances from 360 to 1100 nm at 5 nm intervals in 6 nm bands were measured with a laboratory spectrometer for samples of the components of balsam fir and white spruce trees defoliated by the spruce budworm. These components included current-year needles, 1-year-old needles, 2-year and older needles, budworm feeding debris, twigs, bark, and lichen. Current-year needles had significantly higher reflectances than older needles in the green and yellow parts of the spectrum. Feeding debris, which is visually red, had a smooth spectral curve of increasing reflectance with wavelength. The greatest difference between needles and feeding debris was in the short near-infrared wavelengths and at the chlorophyll absorption maximum near 670 nm. The reflectance of twigs and bark changed with age and exposure to weathering. Variability in their reflectance was large. There were no distinct narrow band features of twig or feeding debris reflectance, which would be characteristic of defoliation. Lichen is highly reflective, and its presence on branches of defoliated trees will greatly alter branch reflectance characteristics. Changes in spectral reflectance of trees throughout the various stages of a spruce budworm outbreak depend on a complex interrelationship of the reflectances of individual components which, in turn, are complex and changing. For. Sci. 35(2):582-600.
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Winther, Jan-Gunnar. "Spectral bi-directional reflectance of snow and glacier ice measured in Dronning Maud Land, Antarctica." Annals of Glaciology 20 (1994): 1–5. http://dx.doi.org/10.3189/1994aog20-1-1-5.
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Visible and near-infrared spectral reflectances of snow and superimposed ice were measured in Dronning Maud Land, Antarctica, during the 1992-93 austral summer. Spectral-reflectance curves of both snow and superimposed ice remain high ( > 80%) in the visible region. A pronounced decrease in reflectance appears in the near-infrared, especially for superimposed ice. Superimposed ice with a 1 cm thick surface layer of ice-bound snow crystals had a considerably higher reflectance than superimposed ice containing only a few snow crystals. Furthermore, these data prove that snow and superimposed ice reflect solar radiation specularly and suggest that the anisotropy strengthens with increasing wavelengths. Integrated in-situ reflectances corresponding to Landsat TM bands 1-4 show that TM band 1 is least affected, whereas TM band 4 is most affected by anisotropy. Furthermore, the anisotropy increases with increasing off-nadir viewing angles up to an angle corresponding to 90°-θs(θs= solar elevation). For a 15° off-nadir sensor-observation angle, the average snow reflectance for TM bands 1--4 is about 10% higher than at nadir. Similarly, the apparent reflectance can be more than 50% higher than the nadir reflectance for larger observation angles. Consequently, if satellite-derived reflectances are going to be considered as absolute values, a topographic-correction model is needed to correct for the effects of anisotropy.
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Winther, Jan-Gunnar. "Spectral bi-directional reflectance of snow and glacier ice measured in Dronning Maud Land, Antarctica." Annals of Glaciology 20 (1994): 1–5. http://dx.doi.org/10.1017/s0260305500016141.
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Visible and near-infrared spectral reflectances of snow and superimposed ice were measured in Dronning Maud Land, Antarctica, during the 1992-93 austral summer. Spectral-reflectance curves of both snow and superimposed ice remain high ( > 80%) in the visible region. A pronounced decrease in reflectance appears in the near-infrared, especially for superimposed ice. Superimposed ice with a 1 cm thick surface layer of ice-bound snow crystals had a considerably higher reflectance than superimposed ice containing only a few snow crystals. Furthermore, these data prove that snow and superimposed ice reflect solar radiation specularly and suggest that the anisotropy strengthens with increasing wavelengths. Integrated in-situ reflectances corresponding to Landsat TM bands 1-4 show that TM band 1 is least affected, whereas TM band 4 is most affected by anisotropy. Furthermore, the anisotropy increases with increasing off-nadir viewing angles up to an angle corresponding to 90°-θs(θs= solar elevation). For a 15° off-nadir sensor-observation angle, the average snow reflectance for TM bands 1--4 is about 10% higher than at nadir. Similarly, the apparent reflectance can be more than 50% higher than the nadir reflectance for larger observation angles. Consequently, if satellite-derived reflectances are going to be considered asabsolutevalues, a topographic-correction model is needed to correct for the effects of anisotropy.
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Liao, Hsien-Shun, Ya-Kang Huang, Jian-Yuan Syu-Gu, and En-Te Hwu. "Real-Time Reflectance Measurement Using an Astigmatic Optical Profilometer." Sensors 22, no. 16 (August 19, 2022): 6242. http://dx.doi.org/10.3390/s22166242.
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An astigmatic optical profilometer with a commercial optical pickup head provides benefits, such as high resolution, compact size, and low cost. To eliminate artifacts caused by complex materials with different reflectances, a z-axis modulation mode is proposed to obtain quantitative surface morphology by measuring S curves on all image pixels. Moreover, the slope of the linear region in the S curve shows a positive relationship with the surface reflectance. However, the slope was calculated using an offline curve fitting method, which did not allow real-time reflectance imaging. Furthermore, quantitative reflectance data were unavailable because of the lack of calibration. In this study, we propose a novel method for real-time reflectance imaging by measuring the amplitude of a focus error signal (FES). The calibration results displayed a linear relationship between the FES amplitude and reflectance. The reflectance image of a grating sample with chrome patterns on a glass substrate demonstrates accurate reflectance measurements with a micrometer spatial resolution.
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Gene, Jinhwa, Min Yong Jeon, and Sun Do Lim. "Reflectometers for Absolute and Relative Reflectance Measurements in the Mid-IR Region at Vacuum." Sensors 21, no. 4 (February 7, 2021): 1169. http://dx.doi.org/10.3390/s21041169.
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We demonstrated spectral reflectometers for two types of reflectances, absolute and relative, of diffusely reflecting surfaces in directional-hemispherical geometry. Both are built based on the integrating sphere method with a Fourier-transform infrared spectrometer operating in a vacuum. The third Taylor method is dedicated to the reflectometer for absolute reflectance, by which absolute spectral diffuse reflectance scales of homemade reference plates are realized. With the reflectometer for relative reflectance, we achieved spectral diffuse reflectance scales of various samples including concrete, polystyrene, and salt plates by comparing against the reference standards. We conducted ray-tracing simulations to quantify systematic uncertainties and evaluated the overall standard uncertainty to be 2.18% (k = 1) and 2.99% (k = 1) for the absolute and relative reflectance measurements, respectively.
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Henniger, Hans, Friedrich J. Bohn, Kim Schmidt, and Andreas Huth. "A New Approach Combining a Multilayer Radiative Transfer Model with an Individual-Based Forest Model: Application to Boreal Forests in Finland." Remote Sensing 15, no. 12 (June 12, 2023): 3078. http://dx.doi.org/10.3390/rs15123078.
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To understand forest dynamics under today’s changing environmental conditions, it is important to analyze the state of forests at large scales. Forest inventories are not available for all regions, so it is important to use other additional methods, e.g., remote sensing observations. Increasingly, remotely sensed data based on optical instruments and airborne LIDAR are becoming widely available for forests. There is great potential in analyzing these measurements and gaining an understanding of forest states. In this work, we combine the new-generation radiative transfer model mScope with the individual-based forest model FORMIND to generate reflectance spectra for forests. Combining the two models allows us to account for species diversity at different height layers in the forest. We compare the generated reflectances for forest stands in Finland, in the region of North Karelia, with Sentinel-2 measurements. We investigate which level of forest representation gives the best results and explore the influence of different calculation methods of mean leaf parameters. For the majority of the forest stands, we generated good reflectances with all levels of forest representation compared to the measured reflectance. Good correlations were also found for the vegetation indices (especially NDVI with R2=0.62). This work provides a forward modeling approach for relating forest reflectance to forest characteristics. With this tool, it is possible to analyze a large set of forest stands with corresponding reflectances. This opens up the possibility to understand how reflectance is related to succession and different forest conditions.
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Yamada, Takatoshi, Makoto Hisa, and Masataka Hasegawa. "Optical properties of vertically aligned graphene sheets." MRS Advances 2, no. 02 (2017): 77–82. http://dx.doi.org/10.1557/adv.2017.16.
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ABSTRACT We have developed deposition of vertically aligned graphene sheets on Cu foils by surface wave microwave plasma CVD and the transfer from Cu foil to quartz substrate to evaluate optical reflectances and transmittances of the inherent vertical aligned graphene sheets. Both reflectance and transmittance spectra are almost independent of incident angles in the range between 300 and 800nm. The reflectance is lower than 0.067%, which is lower than those of the commercial black alumite plate. The transmittances are less than the detection limit of the system. It is considered that the obtained low reflectance is attributed to the unique structure of the vertically aligned graphene sheets.
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Takeuchi, Nozomu. "Temporal and spatial variations in spectral reflectance and characteristics of surface dust on Gulkana Glacier, Alaska Range." Journal of Glaciology 55, no. 192 (2009): 701–9. http://dx.doi.org/10.3189/002214309789470914.
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AbstractSpectral reflectances in the visible to near-infrared wavelength range (350–1050 nm) were measured on the surface of Gulkana Glacier, Alaska Range, Alaska, USA, at six different elevations from May to September 2001. The measurements showed variable spectral reflectances on the glacier surface, and the spectra changed over time and elevation. The spectra in May were those of a typical wet snow surface: the reflectance ranged approximately from 0.4 to 0.8, and generally decreased as the wavelength increased. As snowmelt proceeded, the reflectance gradually fell, and specific absorptions appeared in the spectrum at wavelength ranges of 400–600 and 670–680 nm, corresponding to a red snow surface due to snow algal bloom. As the ice surface was exposed, the spectrum finally shifted to a lower (0.1–0.4) and flat reflectance curve, typical of an ice surface contaminated with dust. Analyses of the dust on the glacier surface showed that its quantity and characteristics changed spatially and seasonally and were correlated with spectral albedo. The results showed that the temporal and spatial variations in spectral reflectance on this glacier are due not only to physical properties of the glacier surface, but also to biogenic materials on the surface (e.g red-colored snow algal cells and cryoconite).
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Sogacheva, L., P. Kolmonen, T. H. Virtanen, E. Rodriguez, A. M. Sundström, and G. de Leeuw. "Determination of land surface reflectance using the AATSR dual-view capability." Atmospheric Measurement Techniques Discussions 7, no. 7 (July 23, 2014): 7451–94. http://dx.doi.org/10.5194/amtd-7-7451-2014.
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Abstract. In this study, a method is presented to retrieve the surface reflectance using reflectance measured at the top of the atmosphere for the two views provided by the Along-Track Scanning Radiometer (AATSR). In the first step, the aerosol optical depth (AOD) is obtained using the AATSR dual view algorithm (ADV) by eliminating the effect of the surface on the measured radiances. Hence the AOD is independent of surface properties and can thus be used in the second step to provide the aerosol part of the atmospheric correction which is needed for the surface reflectance retrieval. The method is applied to provide monthly maps of both AOD and surface reflectance at two wavelengths (555 and 659 nm) for the whole year of 2007. The results are validated vs. surface reflectance provided by the AERONET-based Surface Reflectance Validation Network (ASRVN). Correlation coefficients are 0.8 and 0.9 for 555 and 659 nm, respectively. The standard deviation is 0.001 for both wavelengths and the absolute error is less than 0.02. Pixel-by-pixel comparison with MODIS (MODerate resolution Imaging Spectrometer) monthly averaged surface reflectances show a good correlation (0.91 and 0.89 for 555 and 659 nm, respectively) with some (up to 0.05) overestimation by ADV over bright surfaces. The difference between the ADV and MODIS retrieved surface reflectance is smaller than ±0.025 for 68.3% of the collocated pixels at 555 nm and 79.9% of the collocated pixels at 659 nm. An application of the results over Australia illustrates the variation of the surface reflectances for different land cover types. The validation and comparison results suggest that the algorithm can be successfully used for the both AATSR and ATSR-2 (which has characteristics similar to AATSR) missions, which together cover 17 years period of measurements (1995–2012), as well as a prototype for The Sea and Land Surface Temperature Radiometer (SLSTR) to be launched in 2015 onboard the Sentinel-3 satellite.
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Aleksić, Nikoleta. "Modeling of geothermal evolution of sedimentary rocks in East Herzegovina based on vitrinite reflectance." Tehnika 76, no. 6 (2021): 747–55. http://dx.doi.org/10.5937/tehnika2106747a.
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This paper presents the first results of the geothermal evolution modeling in East Herzegovina based on vitrinite reflectance calculations and measurements. Modeling of burial and geothermal was performed using "SimpleMat" software with well known kinetic model of vitrinite reflectance - EASY % Ro. By fitting the calculated reflectance values with mean measured vitrinite reflectances, it was concluded that there was erosion of some 900 m in the area, and that first possible petroleum generation could have started some 100 Ma ago. According to final calibration model that includes additional thickness and subsequent erosion of Paleogene sequence, the Upper Triassic sediments should have maturity from 0.70 to 1.1 % Rr, Lower Jurassic from 0.62 to 0.70 % Rr, whereas Upper Cretaceous sediments should have values from 0.40 to 0.60 % Rr, which is in accordance with measured vitrinite reflectance in 23 samples. Assuming that beginning of oil window in the East Herzegovina correspond to the vitrinite reflectance of 0.50 % Rr, all analyzed Mesozoic samples are at the initial stage of catagenesis ("oil window"), while Cenozoic sediments are at the stage of diagenesis.
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Wolters, Erwin, Carolien Toté, Sindy Sterckx, Stefan Adriaensen, Claire Henocq, Jérôme Bruniquel, Silvia Scifoni, and Steffen Dransfeld. "iCOR Atmospheric Correction on Sentinel-3/OLCI over Land: Intercomparison with AERONET, RadCalNet, and SYN Level-2." Remote Sensing 13, no. 4 (February 11, 2021): 654. http://dx.doi.org/10.3390/rs13040654.
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To validate the iCOR atmospheric correction algorithm applied to the Sentinel-3 Ocean and Land Color Instrument (OLCI), Top-of-Atmosphere (TOA) observations over land, globally retrieved Aerosol Optical Thickness (AOT), Top-of-Canopy (TOC) reflectance, and Vegetation Indices (VIs) were intercompared with (i) AERONET AOT and AERONET-based TOC reflectance simulations, (ii) RadCalNet surface reflectance observations, and (iii) SYN Level 2 (L2) AOT, TOC reflectance, and VIs. The results reveal that, overall, iCOR’s statistical and temporal consistency is high. iCOR AOT retrievals overestimate relative to AERONET, but less than SYN L2. iCOR and SYN L2 TOC reflectances exhibit a negative bias of ~−0.01 and −0.02, respectively, in the Blue bands compared to the simulations. This diminishes for RED and NIR, except for a +0.02 bias for SYN L2 in the NIR. The intercomparison with RadCalNet shows relative differences < ±6%, except for bands Oa02 (Blue) and Oa21 (NIR), which is likely related to the reported OLCI “excess of brightness”. The intercomparison between iCOR and SYN L2 showed R2 = 0.80–0.93 and R2 = 0.92–0.96 for TOC reflectance and VIs, respectively. iCOR’s higher temporal smoothness compared to SYN L2 does not propagate into a significantly higher smoothness for TOC reflectance and VIs. Altogether, we conclude that iCOR is well suitable to retrieve statistically and temporally consistent AOT, TOC reflectance, and VIs over land surfaces from Sentinel-3/OLCI observations.
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Phan, Thu Thi Thanh, Rikimaru Atsushi, Kenta Sakata, Kazuyoshi Takahashi, and Junki Abe. "Estimation of rice vegetation coverage from DVI of Landsat 7 and 8 data." Science and Technology Development Journal 19, no. 2 (June 30, 2016): 138–45. http://dx.doi.org/10.32508/stdj.v19i2.678.
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Monitoring of rice growth is a requirement for high quality rice production. In addtion to plant height, number stem and rice leaf color, vegetation coverage (VC) which represents for percentage of ground covered by rice plant is also considered as an important index to validate rice growth. Thus, the study is to estimate rice vegetation coverage from difference vegetation index (DVI) calculated from reflectance of near-infrared and red band of Landsat 7 and 8 images. The field observations of the reflectance and the VC were carried out in two paddy rice varieties in 2013. Paddy field reflectance was observed by spectrometer Ocean Optics SD2000. The photos of paddies were taken from the height of 1 m by a digital camera in order to calculate the VC. The reflectances of paddy field corresponding to red and near-infrared bands of Landsat 7 and 8 were calculated from the field observation data. Satellite reflectance was also converted from pixel value of Landsat images. According to the data analysis, VC rapidly increased in two fields and got saturation status (VC>90%) at 65 days after transplanting (DAT) in the early July. DVI was approximately 25% when VC saturated. Additionally, DVI had strong correlation with VC with high determination coefficient (r2 =0.9) when VC was less than 90%. Thus, VC were computed from DVI, calculated from reflectances of Landsat images, using a regression model of VC and DVI. From the result of comparison between the estimated and computed VC, the possibility of estimating VC from DVI calculated from Landsat reflectance is confirmed.
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Wilkins, R. W. T., J. R. Wilmshurst, G. Hladky, M. V. Ellacott, and C. P. Buckingham. "THE SUPPRESSION OF VITRINITE REFLECTANCE IN SOME NORTH WEST SHELF WELLS: BARROW-1, JUPITER-1 AND FLAMINGO-1." APPEA Journal 32, no. 1 (1992): 300. http://dx.doi.org/10.1071/aj91024.
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The sediments of the North West Shelf pose several problems for the accurate determination of thermal maturity by vitrinite reflectance. There are some serious discrepancies between the results of different workers; in some wells there is a surprisingly small increase of reflectance with depth, and it is sometimes difficult to honour these data in thermal maturity modelling. There appear to be two major sources of error in the reflectance data. These are firstly, the effect known as 'suppression' of vitrinite reflectance, and secondly, the difficulty of identifying the vitrinite population in dispersed organic matter.These problems may be addressed by the fluorescence alteration technique which is closely related to vitrinite reflectance but has two special advantages. Firstly, it depends on an analysis of the fluorescence alteration response of a small representative population of organic matter in which the individual macerals need not be identified. Secondly, anomalous vitrinites with suppressed vitrinite reflectance are readily characterized, and the corrected equivalent reflectances determined.The technique has been tested on three North West Shelf petroleum exploration wells, Barrow-1, Jupiter-1 and Flamingo-1. Major discrepancies between measured and equivalent vitrinite reflectance appear to originate in part from the difficulty of identifying the vitrinite population in dispersed organic matter from marine sediments. There is also evidence of suppression of vitrinite reflectance in most samples from Barrow-1, in the Flamingo Group and Plover Formation of Flamingo-1, and in the upper part of the Mungaroo Formation of Jupiter-1.A model is proposed to facilitate the assessment of measured vitrinite reflectance data from Carnarvon or Bonaparte Basin wells. Suppression effects are likely to have influenced measured vitrinite reflectance results from wells for which the strongest data are obtained from the Lower Cretaceous fluvio-deltaic Barrow Group sediments or their equivalents.
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Knaeps, Els, David Doxaran, Ana Dogliotti, Bouchra Nechad, Kevin Ruddick, Dries Raymaekers, and Sindy Sterckx. "The SeaSWIR dataset." Earth System Science Data 10, no. 3 (August 14, 2018): 1439–49. http://dx.doi.org/10.5194/essd-10-1439-2018.
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Abstract. The SeaSWIR dataset consists of 137 ASD (Analytical Spectral Devices, Inc.) marine reflectances, 137 total suspended matter (TSM) measurements and 97 turbidity measurements gathered at three turbid estuarine sites (Gironde, La Plata, Scheldt). The dataset is valuable because of the high-quality measurements of the marine reflectance in the Short Wave InfraRed I region (SWIR-I: 1000–1200 nm) and SWIR-II (1200–1300 nm) and because of the wide range of TSM concentrations from 48 up to 1400 mg L−1. The ASD measurements were gathered using a detailed measurement protocol and were subjected to a strict quality control. The SeaSWIR marine reflectance is characterized by low reflectance at short wavelengths (<450 nm), peak reflectance values between 600 and 720 nm and significant contributions in the near-infrared (NIR) and SWIR-I parts of the spectrum. Comparison of the ASD water reflectance with simultaneously acquired reflectance from a three-radiometer system revealed a correlation of 0.98 for short wavelengths (412, 490 and 555 nm) and 0.93 for long wavelengths (686, 780 and 865 nm). The relationship between TSM and turbidity (for all sites) is linear, with a correlation coefficient of 0.96. The SeaSWIR dataset has been made publicly available (https://doi.org/10.1594/PANGAEA.886287).
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Leshkevich, George A., Donald W. Deering, Thomas F. Eck, and Suraiya P. Ahmad. "Diurnal Patterns of the Bi-Directional Reflectance of Fresh-Water Ice." Annals of Glaciology 14 (1990): 153–57. http://dx.doi.org/10.3189/s0260305500008478.
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To improve the interpretation of surface cryospheric albedo from satellite sensor data, diurnal measurements of the spectral bi-directional reflectance of a commonly-found fresh-water ice type were made, from which hemispherical reflectance can be derived. The purpose of this study is to document its clear-sky, bi-directional reflectance characteristics in the visible (650–670 nm) and near-infrared (810–840 nm) region, assess the diurnal nature of the reflectance, and quantify the surface anisotropy. Bi-directional reflectances of the re-frozen slush ice measured show a spectral dependence and change significantly with solar zenith angle. Considerable variation occurs at each view angle and among view angles throughout the day. Although diurnal reflectance patterns were similar in both bands, magnitudes varied greatly, being highest in the visible and lowest in the near-infrared region. With the exception of peak saturated (specular) values in the forward scatter direction, bi-directional reflectance was generally highest in the morning when the surface and the illumination were most diffuse in character. The exitance (πN) computed from nadir radiance (N) is compared to the measured hemispheric exitance (M). The πN/M ratios, an index of anisotropy, reveal an anisotropy that increases with increasing solar zenith angle and is more pronounced in the near-infrared region.
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Leshkevich, George A., Donald W. Deering, Thomas F. Eck, and Suraiya P. Ahmad. "Diurnal Patterns of the Bi-Directional Reflectance of Fresh-Water Ice." Annals of Glaciology 14 (1990): 153–57. http://dx.doi.org/10.1017/s0260305500008478.
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To improve the interpretation of surface cryospheric albedo from satellite sensor data, diurnal measurements of the spectral bi-directional reflectance of a commonly-found fresh-water ice type were made, from which hemispherical reflectance can be derived. The purpose of this study is to document its clear-sky, bi-directional reflectance characteristics in the visible (650–670 nm) and near-infrared (810–840 nm) region, assess the diurnal nature of the reflectance, and quantify the surface anisotropy. Bi-directional reflectances of the re-frozen slush ice measured show a spectral dependence and change significantly with solar zenith angle. Considerable variation occurs at each view angle and among view angles throughout the day. Although diurnal reflectance patterns were similar in both bands, magnitudes varied greatly, being highest in the visible and lowest in the near-infrared region. With the exception of peak saturated (specular) values in the forward scatter direction, bi-directional reflectance was generally highest in the morning when the surface and the illumination were most diffuse in character. The exitance (πN) computed from nadir radiance (N) is compared to the measured hemispheric exitance (M). The πN/M ratios, an index of anisotropy, reveal an anisotropy that increases with increasing solar zenith angle and is more pronounced in the near-infrared region.
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Tominaga, Shoji, and Hideaki Sakai. "Spectral Reflectance Estimation from Camera Responses Using Local Optimal Dataset." Journal of Imaging 9, no. 2 (February 17, 2023): 47. http://dx.doi.org/10.3390/jimaging9020047.
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A novel method is proposed to estimate surface-spectral reflectance from camera responses using a local optimal reflectance dataset. We adopt a multispectral imaging system that involves an RGB camera capturing multiple images under multiple light sources. A spectral reflectance database is utilized to locally determine the candidates to optimally estimate the spectral reflectance. The proposed estimation method comprises two stages: (1) selecting the local optimal reflectance dataset and (2) determining the best estimate using only the local optimal dataset. In (1), the camera responses are predicted for the respective reflectances in the database, and then the prediction errors are calculated to select the local optimal dataset. In (2), multiple methods are used; in particular, the Wiener and linear minimum mean square error estimators are used to calculate all statistics, based only on the local optimal dataset, and linear and quadratic programming methods are used to solve optimization problems with constraints. Experimental results using different mobile phone cameras show that the estimation accuracy has improved drastically. A much smaller local optimal dataset among spectral reflectance databases is enough to obtain the optimal estimates. The method has potential applications including fields of color science, image science and technology, computer vision, and graphics.
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Sogacheva, L., P. Kolmonen, T. H. Virtanen, E. Rodriguez, A. M. Sundström, and G. de Leeuw. "Determination of land surface reflectance using the AATSR dual-view capability." Atmospheric Measurement Techniques 8, no. 2 (February 22, 2015): 891–906. http://dx.doi.org/10.5194/amt-8-891-2015.
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Abstract. In this study, a method is presented to retrieve the surface reflectance using the radiances measured at the top of the atmosphere for the two views provided by the Advanced Along-Track Scanning Radiometer (AATSR). In the first step, the aerosol optical depth (AOD) is obtained using the AATSR dual-view algorithm (ADV) by eliminating the effect of the surface on the measured radiances. Hence the AOD is independent of surface properties and can thus be used in the second step to provide the aerosol part of the atmospheric correction which is needed for the surface reflectance retrieval. The method is applied to provide monthly maps of both AOD and surface reflectance at two wavelengths (555 and 659 nm) for the whole year of 2007. The results are validated versus surface reflectance provided by the AERONET-based Surface Reflectance Validation Network (ASRVN). Correlation coefficients are 0.8 and 0.9 for 555 and 659 nm, respectively. The standard deviation is 0.001 for both wavelengths and the absolute error is less than 0.02. Pixel-by-pixel comparison with MODIS (Moderate Resolution Imaging Spectrometer) monthly averaged surface reflectances show a good correlation (0.91 and 0.89 for 555 and 659 nm, respectively) with somewhat higher values (up to 0.05) obtained by ADV over bright surfaces. The difference between the ADV- and MODIS-retrieved surface reflectances is smaller than ±0.025 for 68.3% of the collocated pixels at 555 nm and 79.9% of the collocated pixels at 659 nm. An application of the results over Australia illustrates the variation in the surface reflectances for different land cover types. The validation and comparison results suggest that the algorithm can be successfully used for both the AATSR and ATSR-2 (which has characteristics similar to AATSR) missions, which together cover a 17-year period of measurements (1995–2012), as well as a prototype for the Sea and Land Surface Temperature Radiometer (SLSTR) planned to be launched in the fall of 2015 onboard the Sentinel-3 satellite.
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Hidaka, Hironori, Yusuke Monno, and Masatoshi Okutomi. "Spectral Reflectance Estimation Using Projector with Unknown Spectral Power Distribution." Color and Imaging Conference 2020, no. 28 (November 4, 2020): 205–9. http://dx.doi.org/10.2352/issn.2169-2629.2020.28.32.
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A lighting-based multispectral imaging system using an RGB camera and a projector is one of the most practical and low-cost systems to acquire multispectral observations for estimating the scene's spectral reflectance information. However, existing projector-based systems assume that the spectral power distribution (SPD) of each projector primary is known, which requires additional equipment such as a spectrometer to measure the SPD. In this paper, we present a method for jointly estimating the spectral reflectance and the SPD of each projector primary. In addition to adopting a common spectral reflectance basis model, we model the projector's SPD by a low-dimensional model using basis functions obtained by a newly collected projector's SPD database. Then, the spectral reflectances and the projector's SPDs are alternatively estimated based on the basis models. We experimentally show the performance of our joint estimation using a different number of projected illuminations and investigate the potential of the spectral reflectance estimation using a projector with unknown SPD.
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Lee, Hongtak, and JongMin Yeom. "Hyperspectral Irradiance Data for a Comparison and an Analysis of Optical Satellite Spectral Observation: Based on Seogwipo Forest Flux Tower." GEO DATA 1, no. 1 (December 31, 2019): 7–12. http://dx.doi.org/10.22761/dj2019.01.01.002.
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Comparison with ground-truth data is essential for developing and applying remote sensing algorithm towards the Earth surface. Unfortunately, major sources of domestic ground-truth data are depending on field- campaign with limited period because of insufficient all-time observation facilities within a domestic region. Korea Aerospace Research Institute, KARI, is planning to construct and operate surface observation tower to provide remote sensing infrastructure. This study was conducted as a pilot program of the observation tower construction and targeted to observe surface reflectance. The observation was made for about 21 months from May 2017. Two hyper-spectroradiometers were installed on top of a forest flux tower at Mt. Halla to measure hyperspectral up/down-welling irradiance, and surface reflectance was derived simply from their ratio. The derived surface reflectance was compared to surface reflectance values estimated from LANDSAT8 VNIR images, and the two surface reflectances coincided while showing effectiveness of the derived surface reflectance. The data acquired from this study would be able to provide background information for the expected surface observation tower, as well as actual ground-truth data for remote sensing application upon Mt. Halla area.
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Leppänen, Leena, and Anna Kontu. "Analysis of QualitySpec Trek Reflectance from Vertical Profiles of Taiga Snowpack." Geosciences 8, no. 11 (November 6, 2018): 404. http://dx.doi.org/10.3390/geosciences8110404.
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Snow microstructure is an important factor for microwave and optical remote sensing of snow. One parameter used to describe it is the specific surface area (SSA), which is defined as the surface-area-to-mass ratio of snow grains. Reflectance at near infrared (NIR) and short-wave infrared (SWIR) wavelengths is sensitive to grain size and therefore also to SSA through the theoretical relationship between SSA and optical equivalent grain size. To observe SSA, the IceCube measures the hemispherical reflectance of a 1310 nm laser diode from the snow sample surface. The recently developed hand-held QualitySpec Trek (QST) instrument measures the almost bidirectional spectral reflectance in the range of 350–2500 nm with direct contact to the object. The geometry is similar to the Contact Probe, which was previously used successfully for snow measurements. The collected data set includes five snow pit measurements made using both IceCube and QST in a taiga snowpack in spring 2017 in Sodankylä, Finland. In this study, the correlation between SSA and a ratio of 1260 nm reflectance to differentiate between 1260 nm and 1160 nm reflectances is researched. The correlation coefficient varied between 0.85 and 0.98, which demonstrates an empirical linear relationship between SSA and reflectance observations of QST.
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Steinke, J. M., and A. P. Shepherd. "Reflectance measurements of hematocrit and oxyhemoglobin saturation." American Journal of Physiology-Heart and Circulatory Physiology 253, no. 1 (July 1, 1987): H147—H153. http://dx.doi.org/10.1152/ajpheart.1987.253.1.h147.
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Fiberoptic oximeters measure oxyhemoglobin saturation from the optical reflectance of whole blood, but the calibration of such oximeters is hematocrit dependent. Therefore, using photon-diffusion theory and an empirical approach, we have developed a new reflectance method that determines hematocrit and correspondingly corrects the oxyhemoglobin-saturation measurement. Our method employs four fiber-optic light guides, a photodetector, and three inexpensive light-emitting diodes (one with emissions at 660 nm and two at 813 nm). Hematocrit is determined from the ratio of reflectances from the differently spaced emitting fibers at 813 nm and is used to correct the 813-660 nm measurement of oxyhemoglobin saturation. In red cell suspensions, the mean difference between reflectance measurements of hematocrit and conventional determinations was only 2.09% (r = 0.99), and when compared with conventional gasometric measurements of oxyhemoglobin saturation, the reflectance method yielded the same calibration curve for different hematocrits and gave a mean difference of only 2.67%. Although the technique is demonstrated with a cuvette appropriate for an extracorporeal circulation in animal experiments, it could possibly be further developed for fiber-optic catheter oximeters.
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Creamer, Rebecca, Soumaila Sanogo, Osama A. El-Sebai, Jared Carpenter, and Robert Sanderson. "Kaolin-based Foliar Reflectant Affects Physiology and Incidence of Beet Curly Top Virus but not Yield of Chile Pepper." HortScience 40, no. 3 (June 2005): 574–76. http://dx.doi.org/10.21273/hortsci.40.3.574.
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Kaolin reflectant treatments have been shown to reduce stress due to the environment, pests, and pathogens in many plants. We tested the effect of kaolin on yield, beet curly top virus (BCTV) incidence, and physiological parameters (measured as hyperspectral reflectance) of field-grown chile pepper (Capsicum annuum L.) in southern New Mexico. Curly top incidence was significantly lower in kaolin-treated chile blocks than untreated blocks. Peppers treated with the kaolin-reflectant showed significantly less water stress and higher photochemical reflectance than untreated plants during active growth periods. Treated plants had significantly higher levels of chlorophyll a and higher reflectance than untreated plants. Yield from treated plants was not significantly different from that from untreated plants. We did not detect any deleterious effects on peppers due to application of kaolin. Kaolin treatments suppressed beet curly top virus on chile and reduced water stress parameters during the hottest months of the growing season, suggesting that it would be useful in New Mexico chile production in years with moderate disease pressure.
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Christopher, S. A. "Simulation of GOES-R ABI aerosol radiances using WRF-CMAQ: a case study approach." Atmospheric Chemistry and Physics Discussions 13, no. 7 (July 12, 2013): 18713–48. http://dx.doi.org/10.5194/acpd-13-18713-2013.
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Abstract. The primary focus of this paper is to simulate visible and near-infrared reflectances of the GOES-R Advanced Baseline Imager (ABI) for cases of high aerosol loading containing regional haze and smoke over the eastern United States. The simulations are performed using the Weather Research and Forecasting (WRF), Sparse Matrix Operator Kernel Emissions (SMOKE), and Community Multiscale Air Quality (CMAQ) models. Geostationary satellite-derived biomass burning emissions are also included as an input to CMAQ. Using the CMAQ aerosol concentrations and Mie calculations, radiance is computed from the discrete ordinate atmospheric radiative transfer model. We present detailed methods for deriving aerosol extinction from WRF and CMAQ outputs. Our results show that the model simulations create a realistic set of reflectance in various aerosol scenarios. The simulated reflectance provides distinct spectral features of aerosols which is then compared to data from the Moderate Resolution Imaging Spectroradiometer (MODIS). We also present a simple technique to synthesize green band reflectance (which will not be available on the ABI), using the model-simulated blue and red band reflectance. This study is an example of the use of air quality modeling in improving products and techniques for Earth observing missions.
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Hudspith, Victoria A., Claire M. Belcher, Jennifer Barnes, Carolyn B. Dash, Ryan Kelly, and Feng Sheng Hu. "Charcoal reflectance suggests heating duration and fuel moisture affected burn severity in four Alaskan tundra wildfires." International Journal of Wildland Fire 26, no. 4 (2017): 306. http://dx.doi.org/10.1071/wf16177.
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Wildfires are anticipated to increase in frequency and extent in the Arctic tundra. In the unprecedented 2010 fire season, 37 tundra fires burned 435 km2 of the Noatak National Preserve, Alaska. We sampled sixteen soil monoliths from four of these burned areas, which based on microsite burn severity assessments ranged from scorched to moderate–high. Surface charcoals were later studied using reflectance microscopy, as charcoal reflectance may semiquantitatively indicate the duration of heating experienced by a given fuel. Here, the combination of high fuel moisture contents and rapid consumption of fine tussock fuels likely resulted in short fire residence times across the four burned areas, giving an overall low median charcoal reflectance for the entire assemblage (0.82%Romedian). The low charcoal reflectances of the ground fuels provide further evidence for limited heat transference to the organic soil (bryophytes, 0.57 ± 0.17%Romedian; duff and litter, 0.83 ± 0.33%Romedian). The range of observed microsite burn severities is therefore likely attributable to localised variations in above- and ground fuel moisture contents resulting in heterogeneously burned fuels. Consequently, charcoal reflectance is able to provide additional information about current fire behaviour that may improve our understanding of tussock–shrub tundra fires in the future.
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Ito, Y., and Y. Otsuki. "Localization of Apoptotic Cells in the Human Epidermis by an In Situ DNA Nick End-labeling Method Using Confocal Reflectant Laser Microscopy." Journal of Histochemistry & Cytochemistry 46, no. 6 (June 1998): 783–86. http://dx.doi.org/10.1177/002215549804600613.
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We describe an immunohistochemical method that allows the detection of apoptotic cells in human epidermis by use of confocal laser reflectance and antibody-immunogold-silver complexes. For this purpose, the site of free 3′-OH DNA ends was detected by the reflectance from heavy metal products (anti-digoxigenin antibody-immunogold-silver complexes) instead of 3, 3′ -diaminobenzidine (DAB) reaction products in the conventional in situ nick end-labeling of DNA strand breaks (ISEL) technique. Localization of double-stranded DNA was demonstrated by the autofluorescence of methyl green. The ISEL technique using confocal reflectant laser microscopy (CRLM) clearly showed the most intense reflectance in the nuclei of granular cells, in contrast to only a weaker reflectance in those of basal cells. On the other hand, the extent of autofluorescence of methyl green was significantly more intense in the nuclei of basal cells and showed a reciprocal relation to that of the reflectance. Therefore, granular cells were most prone to apoptosis and did not contain double-stranded DNA, as indicated by the lack of stainability with methyl green. In addition, this method demonstrating the simultaneous localization of both free 3′-OH DNA ends and double-stranded DNA proved to have a wide range of applications, including the study of other DNA autolytic processes.
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Aas, E., N. K. H⊘jerslev, and J. H⊘kedal. "Conversion of sub-surface reflectances to above-surface MERIS reflectance." International Journal of Remote Sensing 30, no. 21 (October 16, 2009): 5767–91. http://dx.doi.org/10.1080/01431160902744803.
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Roskovensky, J. K., and K. N. Liou. "Simultaneous Determination of Aerosol and Thin Cirrus Optical Depths over Oceans from MODIS Data: Some Case Studies." Journal of the Atmospheric Sciences 63, no. 9 (September 1, 2006): 2307–23. http://dx.doi.org/10.1175/jas3747.1.
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Abstract The importance of separating thin cirrus and aerosols from satellite remote sensing to produce broader and more accurate fields for the determination of respective radiative forcings is highlighted. This has been accomplished through the development of a new methodology for retrieving both thin cirrus and aerosol optical depths simultaneously over oceans from the Moderate Resolution Imaging Spectroradiometer (MODIS) data. This method employs a procedure to quantify and remove the thin cirrus contribution to the observed reflectance through a correlation of visible and 1.38-μm reflectances so that the aerosol signal can be extracted. Aerosol optical depths are then retrieved through comparisons with the simulated reflectances created a priori. Using the aerosol optical depth along with the specific viewing geometry and surface reflectance as pointers to locations in a lookup table of modeled reflectances, cirrus optical depth and an effective ice crystal size can be retrieved. An iterative scheme has been created that uses the retrieved effective cirrus ice crystal size to account for the effect that the particle size distribution has on the correlation of visible and 1.38-μm reflectance. Retrievals of both aerosol and thin cirrus optical depths over the Atmospheric Radiation Measurement (ARM) Tropical Western Pacific (TWP) site of Nauru performed on a limited number of cases have proven to be consistent with values determined from ground measurements. Also, comparisons with the MODIS aerosol retrievals over a broad area of ocean have highlighted the potential usefulness of this procedure in increasing the amount of potential aerosol information recovered and removing the ever-present thin cirrus contamination.
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Lindberg, James D. "Absolute diffuse reflectance from relative reflectance measurements." Applied Optics 26, no. 14 (July 15, 1987): 2900. http://dx.doi.org/10.1364/ao.26.002900.
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Bacour, Cédric, François-Marie Bréon, Louis Gonzalez, Ivan Price, Jan-Peter Muller, and Anne Straume. "Simulating Multi-Directional Narrowband Reflectance of the Earth’s Surface Using ADAM (A Surface Reflectance Database for ESA’s Earth Observation Missions)." Remote Sensing 12, no. 10 (May 23, 2020): 1679. http://dx.doi.org/10.3390/rs12101679.
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The ADAM (A Surface Reflectance Database for ESA’s Earth Observation Missions) product (a climatological database coupled to its companion calculation toolkit) enables users to simulate realistic hyperspectral and directional global Earth surface reflectances (i.e., top-of-canopy/bottom-of-atmosphere) over the 240–4000 nm spectral range (at 1-nm resolution) and in any illumination/observation geometry, at 0.1° × 0.1° spatial resolution for a typical year. ADAM aims to support the preparation of optical Earth observation missions as well as the design of operational processing chains for the retrieval of atmospheric parameters by characterizing the expected surface reflectance, accounting for its anisotropy. Firstly, we describe (1) the methods used in the development of the gridded monthly ADAM climatologies (over land surfaces: monthly means of normalized reflectances derived from MODIS observations in seven spectral bands for the year 2005; over oceans: monthly means over the 1999–2009 period of chlorophyll content from SeaWiFS and of wind speed from SeaWinds), and (2) the underlying modeling approaches of ADAM toolkit to simulate the spectro-directional variations of the reflectance depending on the assigned surface type. Secondly, we evaluate ADAM simulation performances over land surfaces. A comparison against POLDER multi-spectral/multi-directional measurements for year 2008 shows reliable simulation results with root mean square differences below 0.027 and R2 values above 0.9 for most of the 14 land cover IGBP classes investigated, with no significant bias identified. Only for the “Snow and ice” class is the performance lower pointing to a limitation of climatological data to represent actual snow properties. An evaluation of the modeled reflectance in the specific backscatter direction against CALIPSO data reveals that ADAM tends to overestimate (underestimate) the so-called “hot-spot” by a factor of about 1.5 (1.5 to 2) for barren (vegetated) surfaces.
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Ma, Xu, and Yong Liu. "A Modified Geometrical Optical Model of Row Crops Considering Multiple Scattering Frame." Remote Sensing 12, no. 21 (November 2, 2020): 3600. http://dx.doi.org/10.3390/rs12213600.
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The canopy reflectance model is the physical basis of remote sensing inversion. In canopy reflectance modeling, the geometric optical (GO) approach is the most commonly used. However, it ignores the description of a multiple-scattering contribution, which causes an underestimation of the reflectance. Although researchers have tried to add a multiple-scattering contribution to the GO approach for forest modeling, different from forests, row crops have unique geometric characteristics. Therefore, the modeling approach originally applied to forests cannot be directly applied to row crops. In this study, we introduced the adding method and mathematical solution of integral radiative transfer equation into row modeling, and on the basis of improving the overlapping relationship of the gap probabilities involved in the single-scattering contribution, we derived multiple-scattering equations suitable for the GO approach. Based on these modifications, we established a row model that can accurately describe the single-scattering and multiple-scattering contributions in row crops. We validated the row model using computer simulations and in situ measurements and found that it can be used to simulate crop canopy reflectance at different growth stages. Moreover, the row model can be successfully used to simulate the distribution of reflectances (RMSEs < 0.0404). During computer validation, the row model also maintained high accuracy (RMSEs < 0.0062). Our results demonstrate that considering multiple scattering in GO-approach-based modeling can successfully address the underestimation of reflectance in the row crops.
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Dumont, Marie, Frederic Flin, Aleksey Malinka, Olivier Brissaud, Pascal Hagenmuller, Philippe Lapalus, Bernard Lesaffre, et al. "Experimental and model-based investigation of the links between snow bidirectional reflectance and snow microstructure." Cryosphere 15, no. 8 (August 20, 2021): 3921–48. http://dx.doi.org/10.5194/tc-15-3921-2021.
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Abstract. Snow stands out from materials at the Earth’s surface owing to its unique optical properties. Snow optical properties are sensitive to the snow microstructure, triggering potent climate feedbacks. The impacts of snow microstructure on its optical properties such as reflectance are, to date, only partially understood. However, precise modelling of snow reflectance, particularly bidirectional reflectance, are required in many problems, e.g. to correctly process satellite data over snow-covered areas. This study presents a dataset that combines bidirectional reflectance measurements over 500–2500 nm and the X-ray tomography of the snow microstructure for three snow samples of two different morphological types. The dataset is used to evaluate the stereological approach from Malinka (2014) that relates snow optical properties to the chord length distribution in the snow microstructure. The mean chord length and specific surface area (SSA) retrieved with this approach from the albedo spectrum and those measured by the X-ray tomography are in excellent agreement. The analysis of the 3D images has shown that the random chords of the ice phase obey the gamma distribution with the shape parameter m taking the value approximately equal to or a little greater than 2. For weak and intermediate absorption (high and medium albedo), the simulated bidirectional reflectances reproduce the measured ones accurately but tend to slightly overestimate the anisotropy of the radiation. For such absorptions the use of the exponential law for the ice chord length distribution instead of the one measured with the X-ray tomography does not affect the simulated reflectance. In contrast, under high absorption (albedo of a few percent), snow microstructure and especially facet orientation at the surface play a significant role in the reflectance, particularly at oblique viewing and incidence.
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Owda, Amani Yousef, Neil Salmon, Alexander J. Casson, and Majdi Owda. "The Reflectance of Human Skin in the Millimeter-Wave Band." Sensors 20, no. 5 (March 8, 2020): 1480. http://dx.doi.org/10.3390/s20051480.
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The millimeter-wave band is an ideal part of the electromagnetic radiation to diagnose human skin conditions because this radiation interacts only with tissue down to a depth of a millimetre or less over the band range from 30 GHz to 300 GHz. In this paper, radiometry is used as a non-contact sensor for measuring the human skin reflectance under normal and wet skin conditions. The mean reflectance of the skin of a sample of 50 healthy participants over the (80–100) GHz band was found to be ~0.615 with a standard deviation of ~0.088, and an experimental measurement uncertainty of ±0.005. The thinner skin regions of the back of the hand, the volar forearms and the inner wrist had reflectances 0.068, 0.068 and 0.062 higher than the thicker skin regions of the palm of the hand, the dorsal forearm and the outer wrist skin. Experimental measurements of human skin reflectance in a normal and a wet state on the back of the hand and the palm of the hand regions indicated that the mean differences in the reflectance before and after the application of water were ~0.078 and ~0.152, respectively. These differences were found to be statistically significant as assessed using t-tests (34 paired t-tests and six independent t-tests were performed to assess the significance level of the mean differences in the reflectance of the skin). Radiometric measurements in this paper show the quantitative variations in the skin reflectance between locations, sexes, and individuals. The study reveals that these variations are related to the skin thickness and water content, a capability that has the potential to allow radiometry to be used as a non-contact sensor to detect and monitor skin conditions such as eczema, psoriasis, malignancy, and burn wounds.
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Zhou, Y., D. Brunner, R. J. D. Spurr, K. F. Boersma, M. Sneep, C. Popp, and B. Buchmann. "Accounting for surface reflectance anisotropy in satellite retrievals of tropospheric NO<sub>2</sub>." Atmospheric Measurement Techniques Discussions 3, no. 3 (May 3, 2010): 1971–2012. http://dx.doi.org/10.5194/amtd-3-1971-2010.
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Abstract. Surface reflectance is a key parameter in satellite trace gas retrievals in the UV/visible range and in particular for the retrieval of nitrogen dioxide (NO2) vertical tropospheric columns (VTCs). Current operational retrievals rely on coarse-resolution reflectance data and do not account for the generally anisotropic properties of surface reflectance. Here we present a NO2 VTC retrieval that uses MODIS bi-directional reflectance distribution function (BRDF) data at high temporal (8 days) and spatial (1 km×1 km) resolution in combination with the LIDORT radiative transfer model to account for the dependence of surface reflectance on viewing and illumination geometry. The method was applied to two years of NO2 observations from the Ozone Monitoring Instrument (OMI) over Europe. Due to its wide swath, OMI is particularly sensitive to BRDF effects. Using representative BRDF parameters for various land surfaces, we found that in July (low solar zenith angles) and November (high solar zenith angles) and for typical viewing geometries of OMI, differences between MODIS black-sky albedos and surface bi-directional reflectances are of the order of 0–10% and 0–40%, respectively, depending on the position of the OMI pixel within the swath. In the retrieval, black-sky albedo was treated as a Lambertian (isotropic) reflectance, while for BRDF effects we used the kernel-based approach in the MODIS BRDF product. Air Mass Factors were computed using the LIDORT radiative transfer model based on these surface reflectance conditions. Differences in NO2 VTCs based on the Lambertian and BRDF approaches were found to be of the order of 0–3% in July and 0–20% in November with the extreme values found at large viewing angles. The much larger differences in November are partly due to higher solar zenith angles and partly to the choice of a priori NO2 profiles – the latter typically have more pronounced maxima in the boundary layer during the cold season. However, BRDF impacts vary considerably across Europe due to changes in land surface type and increasing solar zenith angles at higher latitude. Finally, we compare BRDF-based NO2 VTCs with those retrieved using the GOME/TOMS Lambertian equivalent reflectance (LER) data set. Our results indicate that the specific choice of albedo data set is even more important than accounting for surface BRDF effects, and this again demonstrates the strong requirement for more accurate surface reflectance data sets.
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Christopher, S. A. "Simulation of GOES-R ABI aerosol radiances using WRF-CMAQ: a case study approach." Atmospheric Chemistry and Physics 14, no. 7 (April 1, 2014): 3183–94. http://dx.doi.org/10.5194/acp-14-3183-2014.
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Abstract. In anticipation of the upcoming GOES-R launch we simulate visible and near-infrared reflectances of the Advanced Baseline Imager (ABI) for cases of high aerosol loading containing regional haze and smoke over the eastern United States. The simulations are performed using the Weather Research and Forecasting (WRF), Sparse Matrix Operator Kernel Emissions (SMOKE), and Community Multiscale Air Quality (CMAQ) models. Geostationary, satellite-derived, biomass-burning emissions are also included as an input to CMAQ. Using the CMAQ aerosol concentrations and Mie calculations, radiance is computed from the discrete ordinate atmospheric radiative transfer model. We present detailed methods for deriving aerosol extinction from WRF and CMAQ outputs. Our results show that the model simulations create a realistic set of reflectances in various aerosol scenarios. The simulated reflectances provide distinct spectral features of aerosols which are then compared to data from the Moderate Resolution Imaging Spectroradiometer (MODIS). We also present a simple technique to synthesize green band reflectance (which will not be available on the ABI), using the model-simulated blue and red band reflectance. This study is an example of the use of air quality modeling in improving products and techniques for Earth-observing missions.
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Mei, L., Y. Xue, G. de Leeuw, T. Holzer-Popp, J. Guang, Y. Li, L. Yang, et al. "Retrieval of aerosol optical depth over land based on a time series technique using MSG/SERIVI data." Atmospheric Chemistry and Physics Discussions 12, no. 2 (February 3, 2012): 4031–71. http://dx.doi.org/10.5194/acpd-12-4031-2012.
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Abstract. A novel approach for the joint retrieval of aerosol optical depth (AOD) and surface reflectance, using Meteosat Second Generation – Spinning Enhanced Visible and Infrared Imagers (MSG/SEVIRI) observations in two solar channels, is presented. The retrieval is based on a time series (TS) technique, which makes use of the two visible bands at 0.6 μm and 0.8 μm in three orderly scan times (15 min interval between two scans) to retrieve the AOD over land. Using the radiative transfer equation for plane-parallel atmospheres two coupled differential equations for the upward and downward fluxes are derived. The boundary conditions for the upward and downward fluxes at the top and at the bottom of the atmosphere are used in these equations to provide an analytic solution for the surface reflectance. To derive these fluxes, the aerosol single scattering albedo (SSA) and asymmetry factor are required to provide a solution. These are provided from a set of six pre-defined aerosol types with the SSA and asymmetry factor (g). We assume one aerosol type for a grid of 1° × 1° and the surface reflectance changes little between two consequent scans. A k approximation was used in the inversion to find the best solution of atmospheric properties and surface reflectance. The algorithm makes use of numerical minimisation routines to obtain the optimal solution of atmospheric properties and surface reflectance by selection of the most suitable aerosol type from pre-defined sets. Also, it is assumed that the surface reflectance is little influenced by aerosol scattering at 1.6 μm and therefore the ratio of surface reflectances in the solar band for two consequent scans can be well-approximated by the ratio of the reflectances at 1.6 μm. A further assumption is that the surface reflectance varies only slightly over a period of 30 min. A detailed analysis of the retrieval results show that it is suitable for AOD retrieval over land. Six Aerosol Robotic Network (AERONET) sites with different surface types were used for detailed analysis and 42 other AERONET sites were used for validation. From 445 collocations representing stable and homogeneous aerosol type, we found that >75% of MSG-retrieved AOD values compared to AERONET observed values with an error envelope of ±0.05 ± 0.15τ and a high correlation (R > 0.86). The AOD datasets derived using the TS method with SEVIRI data was also compared with collocated AOD products derived from the NASA TERRA and AQUA MODIS data using the dark dense vegetation (DDV) method and the Deep Blue algorithms. Using the TS method, AOD could be retrieved for more pixels than with the NASA Deep Blue algorithm. The AOD values derived compare favourably.
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Chen, Guojun, Yue Dong, Pieter Peers, Jiawan Zhang, and Xin Tong. "Reflectance scanning." ACM Transactions on Graphics 33, no. 4 (July 27, 2014): 1–11. http://dx.doi.org/10.1145/2601097.2601180.
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Kowalski, Frank. "Reflectance demonstration." Physics Teacher 31, no. 3 (March 1993): 153. http://dx.doi.org/10.1119/1.2343694.
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Wallace, Michael B., Adam Wax, David N. Roberts, and Robert N. Graf. "Reflectance Spectroscopy." Gastrointestinal Endoscopy Clinics of North America 19, no. 2 (April 2009): 233–42. http://dx.doi.org/10.1016/j.giec.2009.02.008.
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Berets, Susan L., and Milan Milosevic. "Extracting Infrared Absolute Reflectance from Relative Reflectance Measurements." Applied Spectroscopy 66, no. 6 (June 2012): 680–84. http://dx.doi.org/10.1366/11-06560.
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Schamberger, Léa, Audrey Minghelli, Malik Chami, and François Steinmetz. "Improvement of Atmospheric Correction of Satellite Sentinel-3/OLCI Data for Oceanic Waters in Presence of Sargassum." Remote Sensing 14, no. 2 (January 14, 2022): 386. http://dx.doi.org/10.3390/rs14020386.
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The invasive species of brown algae Sargassum gathers in large aggregations in the Caribbean Sea, and has done so especially over the last decade. These aggregations wash up on shores and decompose, leading to many socio-economic issues for the population and the coastal ecosystem. Satellite ocean color data sensors such as Sentinel-3/OLCI can be used to detect the presence of Sargassum and estimate its fractional coverage and biomass. The derivation of Sargassum presence and abundance from satellite ocean color data first requires atmospheric correction; however, the atmospheric correction procedure that is commonly used for oceanic waters needs to be adapted when dealing with the occurrence of Sargassum because the non-zero water reflectance in the near infrared band induced by Sargassum optical signature could lead to Sargassum being wrongly identified as aerosols. In this study, this difficulty is overcome by interpolating aerosol and sunglint reflectance between nearby Sargassum-free pixels. The proposed method relies on the local homogeneity of the aerosol reflectance between Sargassum and Sargassum-free areas. The performance of the adapted atmospheric correction algorithm over Sargassum areas is evaluated. The proposed method is demonstrated to result in more plausible aerosol and sunglint reflectances. A reduction of between 75% and 88% of pixels showing a negative water reflectance above 600 nm were noticed after the correction of the several images.
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Niroumand-Jadidi, Milad, Nima Pahlevan, and Alfonso Vitti. "Mapping Substrate Types and Compositions in Shallow Streams." Remote Sensing 11, no. 3 (January 29, 2019): 262. http://dx.doi.org/10.3390/rs11030262.
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Remote sensing of riverbed compositions could enable advances in hydro-morphological and habitat modeling. Substrate mapping in fluvial systems has not received as much attention as in nearshore, optically shallow inland, and coastal waters. As finer spatial-resolution image data become more available, a need emerges to expand research on the remote sensing of riverbed composition. For instance, research to date has primarily been based on spectral reflectance data from above the water surface without accounting for attenuation by the water-column. This study analyzes the impacts of water-column correction for substrate mapping in shallow fluvial systems (depth < 1 m). To do so, we performed three different experiments: (a) analyzing spectroscopic measurements in a hydraulic laboratory setting, (b) simulating water-leaving radiances under various optical scenarios, and (c) evaluating the potential to map bottom composition from a WorldView-3 (WV3) image of a river in Northern Italy. Following the retrieval of depth and diffuse attenuation coefficient ( K d ), bottom reflectances were estimated using a water-column correction method. The results indicated significant enhancements in streambed maps based on bottom reflectances relative to maps produced from above-water spectra. Accounting for deep-water reflectance, embedded in the water-column correction, was demonstrated to have the greatest impact on the retrieval of bottom reflectance in NIR bands, when the water column is relatively thick (>0.5 m) and/or when the water is turbid. We also found that the WV3’s red-edge band (i.e., 724 nm) considerably improved the characterization of submerged aquatic vegetation (SAV) densities from either above-water or retrieved bottom spectra. This study further demonstrated the feasibility of mapping SAV density classes from a WV3 image of the Sarca River in Italy by retrieving the bottom reflectances.
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Jäkel, E., B. Mey, R. Levy, X. Gu, T. Yu, Z. Li, D. Althausen, B. Heese, and M. Wendisch. "Adaption of the MODIS aerosol retrieval algorithm by airborne spectral surface reflectance measurements over urban areas: a case study." Atmospheric Measurement Techniques Discussions 8, no. 7 (July 16, 2015): 7335–71. http://dx.doi.org/10.5194/amtd-8-7335-2015.
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Abstract. MODIS retrievals of the aerosol optical depth (AOD) are biased over urban areas, where surface reflectance is not well characterized. Since the operational MODIS aerosol retrieval for dark targets assumes fixed spectral slopes to calculate the surface reflectance at 0.47 μm, the algorithm may fail in urban areas with different spectral characteristics of the surface reflectance. To investigate this bias we have implemented variable spectral slopes into the operational MODIS aerosol algorithms of Collection 5 (C5) and C6. The variation of slopes is based on airborne measurements of surface reflectances over the city of Zhongshan, China. AOD retrieval results of the operational and the modified algorithms were compared for a MODIS measurement over Zhongshan. For this case slightly lower AOD values were derived using the modified algorithm. The retrieval methods were additionally applied to MODIS data of the Beijing area for a period between 2010–2014 when also AERONET data were available. A reduction of the differences between the AOD retrieved using the modified C5 algorithm and AERONET was found, whereby the mean difference from 0.31 ± 0.11 for the operational C5 and 0.18 ± 0.12 for the operational C6 where reduced to a mean difference of 0.09 ± 0.18 by using the modified C5 retrieval. Furthermore, the sensitivity of the MODIS AOD retrieval for several surface types was investigated. Radiative transfer simulations were performed to model reflectances at top of atmosphere for predefined aerosol properties. The reflectances were used as input for the retrieval methods. It is shown that the operational MODIS AOD retrieval over land reproduces the AOD reference input of 0.85 for dark surface types [retrieved AOD = 0.87 (C5)]. An overestimation of AOD = 0.99 is found for urban surfaces, whereby the modified C5 algorithm shows a good performance with a retrieved value of AOD = 0.86.
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Cheng, Yen-Ben, Elizabeth M. Middleton, Qingyuan Zhang, Lawrence A. Corp, Jonathan Dandois, and William P. Kustas. "The photochemical reflectance index from directional cornfield reflectances: Observations and simulations." Remote Sensing of Environment 124 (September 2012): 444–53. http://dx.doi.org/10.1016/j.rse.2012.05.030.
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Zhou, Y., D. Brunner, R. J. D. Spurr, K. F. Boersma, M. Sneep, C. Popp, and B. Buchmann. "Accounting for surface reflectance anisotropy in satellite retrievals of tropospheric NO<sub>2</sub>." Atmospheric Measurement Techniques 3, no. 5 (September 1, 2010): 1185–203. http://dx.doi.org/10.5194/amt-3-1185-2010.
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Abstract. Surface reflectance is a key parameter in satellite trace gas retrievals in the UV/visible range and in particular for the retrieval of nitrogen dioxide (NO2) vertical tropospheric columns (VTCs). Current operational retrievals rely on coarse-resolution reflectance data and do not account for the generally anisotropic properties of surface reflectance. Here we present a NO2 VTC retrieval that uses MODIS bi-directional reflectance distribution function (BRDF) data at high temporal (8 days) and spatial (1 km × 1 km) resolution in combination with the LIDORT radiative transfer model to account for the dependence of surface reflectance on viewing and illumination geometry. The method was applied to two years of NO2 observations from the Ozone Monitoring Instrument (OMI) over Europe. Due to its wide swath, OMI is particularly sensitive to BRDF effects. Using representative BRDF parameters for various land surfaces, we found that in July (low solar zenith angles) and November (high solar zenith angles) and for typical viewing geometries of OMI, differences between MODIS black-sky albedos and surface bi-directional reflectances are of the order of 0–10% and 0–40%, respectively, depending on the position of the OMI pixel within the swath. In the retrieval, black-sky albedo was treated as a Lambertian (isotropic) reflectance, while for BRDF effects we used the kernel-based approach in the MODIS BRDF product. Air Mass Factors were computed using the LIDORT radiative transfer model based on these surface reflectance conditions. Differences in NO2 VTCs based on the Lambertian and BRDF approaches were found to be of the order of 0–3% in July and 0–20% in November with the extreme values found at large viewing angles. The much larger differences in November are mainly due to stronger BRDF effects at higher solar zenith angles. To a smaller extent, they are also caused by the typically more pronounced maximum of the NO2 a priori profiles in the boundary layer during the cold season, which make the retrieval more sensitive to radiation changes near the surface. However, BRDF impacts vary considerably across Europe due to differences in land surface type and increasing solar zenith angles at higher latitude. Finally, we compare BRDF-based NO2 VTCs with those retrieved using the GOME/TOMS Lambertian equivalent reflectance (LER) data set. The relative differences are mostly below 15% in July but in November the NO2 VTCs from TOMS/GOME are lower by 20–60%. Our results indicate that the specific choice of albedo data set is even more important than accounting for surface BRDF effects, and this again demonstrates the strong requirement for more accurate surface reflectance data sets.
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Baddeley, Roland, and David Attewell. "The Relationship Between Language and the Environment." Psychological Science 20, no. 9 (September 2009): 1100–1107. http://dx.doi.org/10.1111/j.1467-9280.2009.02412.x.
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The surface reflectance of objects is highly variable, ranging between 4% for, say, charcoal and 90% for fresh snow. When stimuli are presented simultaneously, people can discriminate hundreds of levels of visual intensity. Despite this, human languages possess a maximum of just three basic terms for describing lightness. In English, these are white (or light), black (or dark), and gray. Why should this be? Using information theory, combined with estimates of the distribution of reflectances in the natural world and the reliability of lightness recall over time, we show that three lightness terms is the optimal number for describing surface reflectance properties in a modern urban or indoor environment. We also show that only two lightness terms would be required in a forest or rural environment.
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Fieuzal, Remy, Vincent Bustillo, David Collado, and Gerard Dedieu. "Potential of Sentinel-2 Images for Estimating of Soil Resistivity over Agricultural Fields." Proceedings 24, no. 1 (June 5, 2019): 18. http://dx.doi.org/10.3390/iecg2019-06219.
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The aim of this study is to assess the possibilities of the VNIR (Visible and Near InfraRed) and SWIR (Short Wavelength InfraRed) satellite data for estimating intra-plot patterns of soil electrical resistivity consistent with ground measurements. The methodology is based on optical reflectances that constitute the input variables of random forest, alone or in combination with parameters derived from a digital elevation model (DEM). Over a field located in southwestern France, the results show high level of accuracy for the 0–50 and 0–100 cm soil layers (with R² of 0.69 and 0.59, and a relative RMSE of 18% and 16%, respectively), the performances being lower for the 0–170 cm layer (R² of 0.39, relative RMSE of 20%). The combined use of optical reflectances with parameters derived from the DEM slightly improves the performances, whatever the considered layer. The influence of each reflectance on soil electrical resistivity estimates is finally analyzed, showing that the wavelengths acquired in the SWIR have a relative higher importance than VNIR reflectance.