A Survey of Shading and Reflectance Models

Since the beginning of computer graphics, three decades ago, a large number of models intended to describe the behaviour of light on a given point of a surface have been proposed. Almost every author uses his own terminology and/or notation. To understand clearly the similarities and the differences between existing models, reformulating them with a unified notation is essential. This has been done by Hall in 1986. This paper is a new survey of shading and reflectance models, including the most recent models. Moreover, after the lengthy enumeration, some original models are proposed, which attempt to include interesting features of previous disjointed work into new formulations.     

Reflectance spectra of RAMI forest stands in Estonia: Simulations and measurements

Simulated reflectance spectra of three mature hemiboreal forests are compared to top-of-canopy reflectance factor from helicopter measurements in the spectral range of 400-1050 nm. Most of the input parameters of the forest reflectance model FRT used in the simulations have been measured in situ. The same data were used in the fourth phase of the Radiation Transfer Model Intercomparison (RAMI). The reasons of the discrepancies between simulated and measured spectra are analyzed.     

1980~2019年北疆积雪时空变化与气候和植被的关系

利用1980~2019年中国长时间序列的AVHRR逐日无云积雪面积产品和气象站实测雪深资料计算积雪日数、积雪初日、积雪终日、积雪期、雪深等积雪物候参数,研究积雪物候的时空分布变化,同时结合ECMWF-ERA5再分析资料和GIMMS NDVI3g数据集分别提取气象因子（气温、降水）和植被因子（返青期、枯黄期、生长期）,探究北疆积雪物候变化对气象因子和植被因子的响应。结果表明：北疆近40 a间的平均积雪日数为81.62 d/a,73%的区域为稳定积雪区,积雪初日在11月、终日在3月,积雪期为每年11月初至次年3月底4月初;空间上呈现不均匀分布,其中阿勒泰山地区、天山地区、大部分塔城盆地和额尔齐斯谷地区为主要积雪区,1980~2019年间北疆积雪覆盖面积比例、积雪日数和积雪期逐年降低,积雪初日基本没变,但积雪终日显著提前;ECMWF-ERA5再分析资料表明1980~2019年北疆积雪期降水量无明显变化,但积雪覆盖面积比例显著降低,说明降雪区雪深可能增加,这与北疆气象站实测雪深逐渐增加结果相吻合;平均气温与积雪期积雪覆盖面积比例、积雪日数、积雪期长度相关性较大,呈现显著负相关,积雪期降水量与积雪物候参数呈现正相关;积雪物候及其气候效应引起北疆自然植被返青期显著提前,植被生长期延长的特征。     

Satellite radar and optical remote sensing for earthquake damage detection: results from different case studies

In case of a seismic event, a fast and draft damage map of the hit urban areas can be very useful, in particular when the epicentre of the earthquake is located in remote regions, or the main communication systems are damaged. Our aim is to analyse the capability of remote sensing techniques for damage detection in urban areas and to explore the combined use of radar (SAR) and optical satellite data. Two case studies have been proposed: Izmit (1999; Turkey) and Bam (2003; Iran). Both areas have been affected by strong earthquakes causing heavy and extended damage in the urban settlements close to the epicentre. Different procedures for damage assessment have been successfully tested, either to perform a pixel by pixel classification or to assess damage within homogeneous extended areas. We have compared change detection capabilities of different features extracted from optical and radar data, and analysed the potential of combining measurements at different frequency ranges. Regarding the Izmit case, SAR features alone have reached 70% of correct classification of damaged areas and 5 m panchromatic optical images have given 82%; the fusion of SAR and optical data raised up to 89% of correct pixel‐to‐pixel classification. The same procedures applied to the Bam test case achieved about 61% of correct classification from SAR alone, 70% from optical data, while data fusion reached 76%. The results of the correlation between satellite remote sensing and ground surveys data have been presented by comparing remotely change detection features averaged within homogeneous blocks of buildings with ground survey data.     

On the reproducibility of field-measured reflectance factors in the context of vegetation studies

This paper describes a study aimed at quantifying uncertainty in field measurements of vegetation canopy hemispherical conical reflectance factors (HCRF). The use of field spectroradiometers is common for this purpose, but the reliability of such measurements is still in question. In this paper we demonstrate the impact of various measurement uncertainties on vegetation canopy HCRF, using a combined laboratory and field experiment employing three spectroradiometers of the same broad specification (GER 1500). The results show that all three instruments performed similarly in the laboratory when a stable radiance source was measured (NEΔL < 1 mW m⁻² sr⁻¹ nm⁻¹ in the range of 400-1000 nm). In contrast, field-derived standard uncertainties (u = SD of 10 consecutive measurements of the same surface measured in ideal atmospheric conditions) significantly differed from the lab-based uncertainty characterisation for two targets: a control (75% Spectralon panel) and a cropped grassland surface. Results indicated that field measurements made by a single instrument of the vegetation surface were reproducible to within ± 0.015 HCRF and of the control surface to within ± 0.006 HCRF (400-1000 nm (± 1σ)). Field measurements made by all instruments of the vegetation surface were reproducible to within ± 0.019 HCRF and of the control surface to within ± 0.008 HCRF (400-1000 nm (± 1σ)). Statistical analysis revealed that even though the field conditions were carefully controlled and the absolute values of u were small, different instruments yielded significantly different reflectance values for the same target. The results also show that laboratory-derived uncertainty quantities do not present a useful means of quantifying all uncertainties in the field. The paper demonstrates a simple method for u characterisation, using internationally accepted terms, in field scenarios. This provides an experiment-specific measure of u that helps to put measurements in context and forms the basis for comparison with other studies.     

Sensitivity of Alpine3D modeled snow cover to modifications in DEM resolution,station coverage and meteorological input quantities

This study presents a comprehensive sensitivity and uncertainty assessment of important input parameters on the Alpine3D modeled snow water equivalent (SWE) for two different alpine catchments. Horizontal resolution of the DEM grid, station coverage and several meteorological input quantities were modified. Decreasing the horizontal resolution from 25 m to 1000 m leads to a 10% higher SWE. Modifications in the spatial coverage of meteorological stations influences the SWE up to 20%. Modifications of meteorological input quantities within some plausible ranges lead to changes in SWE up to 30%. The results demonstrate that Alpine3D input uncertainties are in general in the same range as the typical measurement uncertainty of SWE and the uncertainty of the typical scenario spread of GCM-RCM ensemble runs.     

Assessment of physical work load in epidemiologic studies: concepts,issues and operational considerations

Ergonomic epidemiology is a rapidly increasing field of research providing data on the occurrence of musculoskeletal disorders and possible risk factors. The present paper states, on the basis of a literature overview, that physical work load (mechanical exposure) is poorly denned and measured in most studies on ergonomic epidemiology. On this background the paper: (1) suggests adjustments of mechanical exposure concepts and terminology; (2) concludes that invalid exposure assessment may, to a large extent, explain the lack of quantitative data on relationships between mechanical exposures and musculoskeletal disorders; and (3) suggests some guidelines for future quantitative assessments of mechanical exposure in large populations.     

Subsurface microwave remote sensing of soil-water content: Field studies in the Negev Desert and optical modelling

The population increase in the Middle East and the respective decrease of water resources necessitate innovative methods for utilization and monitoring of water resources. Development of remote sensing tools can pave the way for remote, rapid mapping of soil-water content, control of excessive irrigation, and prevention of water waste. This paper describes a series of experiments conducted in the Negev Desert that were aimed at developing such tools for monitoring soil-water content. The use of visible near infrared and microwave techniques seems suitable. All provide good correlation with soil-water content measured on the ground. However, the microwave techniques presented here using a P-band scatterometer and ERS-2 SAR seem the most promising. Finally the possibility of optical simulation of the microwave processes is presented in an effort to improve the physical basis for empirical studies. A method of fabrication of optical samples that model soils with different water content and different surface roughness is developed, and a system for measuring backscattered signals is designed. It is shown that the reflectivity of a layered medium is a non-monotonic function of the water content. The effect of the surface roughness on the reflection from a strong buried reflector is being studied.     

In-situ measured spectral directional emissivity of snow and ice in the 8–14 μm atmospheric window

The directional emissivity of snow and ice surfaces in the 8–14 μm thermal infrared (TIR) atmospheric window was determined from spectral radiances obtained by field measurements using a portable Fourier transform infrared spectrometer in conjunction with snow pit work. The dependence of the directional emissivity on the surface snow type (grain size and shape) was examined. We obtained emissivity spectra for five different surface types, i.e., fine dendrite snow, medium granular snow, coarse grain snow, welded sun crust snow, and smooth bare ice. The derived emissivities show a distinct spectral contrast at wavelengths λ = 10.5–12.5 μm which is enhanced with increasing the snow grain size. For example, emissivities at both 10.5 μm and 12.5 μm for the nadir angle were 0.997 and 0.984 for the fine dendrite snow, 0.996 and 0.974 for the medium granular snow, 0.995 and 0.971 for the coarse grain snow, 0.992 and 0.968 for the sun crust, and 0.993 and 0.949 for the bare ice, respectively. In addition, the spectral contrast exhibits a strong angular dependence, particularly for the coarser snow and bare ice, e.g., the emissivity at λ = 12.5 μm for the off-nadir angle of 75° reaches down to 0.927, 0.896, and 0.709 for the coarse grain snow, sun crust, and bare ice cases, respectively. The angular dependent emissivity spectra of the bare ice were quite consistent with the spectra predicted by the Fresnel reflectance theory. The observed results firmly demonstrate that the directional emissivity of snow in the TIR can vary depending upon the surface snow type. The high variability of the spectral emissivity of snow also suggests the possibility to discriminate between snow and ice types from space using the brightness temperature difference in the atmospheric window.     

Reflectance seasonality and its relation to the canopy leaf area index in an eastern Siberian larch forest: Multi-satellite data and radiative transfer analyses

Reliable monitoring of seasonality in the forest canopy leaf area index (LAI) in Siberian forests is required to advance the understanding of climate-forest interactions under global environmental change and to develop a forest phenology model within ecosystem modeling. Here, we compare multi-satellite (AVHRR, MODIS, and SPOT/VEGETATION) reflectance, normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and LAI with aircraft-based spectral reflectance data and field-measured forest data acquired from April to June in 2000 in a larch forest near Yakutsk, Russia. Field data in a 30 × 30-m study site and aircraft data observed around the field site were used. Larch is a dominant forest type in eastern Siberia, but comparison studies that consider multi-satellite data, aircraft-based reflectance, and field-based measurement data are rarely conducted. Three-dimensional canopy radiative transfer calculations, which are based on Antyufeev and Marshak's [Antyufeev, V.S., & Marshak, A.L. (1990). Monte Carlo method and transport equation in plant canopies, Remote Sensing of Environment, 31, 183-191] Monte Carlo photon transport method combined with North's [North, P.R. (1996). Three-dimensional forest light interaction model using a Monte Carlo method, IEEE Transactions on Geoscience and Remote Sensing, 34(4), 946-956] geometric-optical hybrid forest canopy scene, helped elucidate the relationship between canopy reflectance and forest structural parameters, including several forest floor conditions. Aircraft-based spectral measurements and the spectral response functions of all satellite sensors confirmed that biases in reflectance seasonality caused by differences in spectral response functions among sensors were small. However, some reflectance biases occur among the near infrared (NIR) reflectance data from satellite products; these biases were potentially caused by absolute calibration errors or cloud/cloud shadow contamination. In addition, reflectance seasonality in AVHRR-based NIR data was very small compared to other datasets, which was partially due to the spring-to-summer increase in the amount of atmospheric water vapor. Radiative transfer simulations suggest that bi-directional reflectance effects were small for the study site and observation period; however, changes in tree density and forest floor conditions affect the absolute value of NIR reflectance, even if the canopy leaf area condition does not change. Reliable monitoring of canopy LAI is achieved by minimizing these effects through the use of NIR reflectance difference, i.e., the difference in reflectance on the observation day from the reflectance on a snow-free/pre-foliation day. This may yield useful and robust parameters for multi-satellite monitoring of the larch canopy LAI with less error from intersensor biases and forest structure/floor differences. Further validation with field data and combined use of other index (e.g. normalized difference water index, NDWI) data will enable an extension of these findings to all Siberian deciduous forests.     

Variation and directional anisotropy of reflectance at the crown scale — Implications for tree species classification in digital aerial images

Tree species classification is still solved at insufficient reliability in airborne optical data. The variation caused by directional reflectance anisotropy hampers image-based solutions. In addition, trees show considerable within-species variation in reflectance properties. We examined these phenomena at the single-tree level, using the Leica ADS40 line sensor and XPro software, which constitute the first photogrammetric large-format multispectral system to provide target reflectance images. To analyze the influence of illumination conditions in the canopy, we developed a method in which the crown shape as well as between-tree occlusions and shading were modeled, using dense LiDAR data. The precision of the ADS40 reflectance images in well-defined surfaces was 5% as coefficient of variation when 1−4-km image data were fused. The range of reflectance anisotropy was ± 30% for trees near the solar principal plane, with differences between bands and species. Because of the anisotropy differences observed, the spectral separability of the tree species in different bands is dependent on the view-illumination geometry. The within-species variation was high; the coefficient of variation was 13−31%. The contribution of tree and stand variables to anisotropy-normalized reflectance variation was examined. The effects of the species composition of adjacent trees were substantial in NIR and this variation hampers spectral classification in mixed stands. We also studied species- and band-specific intracrown brightness patterns, and we suggest their use as high-order image features in species classification. A species classification accuracy of up to 80% was obtained using 4-km data, which showed the high potential of the ADS40.     

Laser Thomson scattering and optical emission studies of striated PDP micro‐discharge plasmas

Abstract— Properties of a plasma‐display‐panel (PDP) like discharge were examined by emission and laser Thomson scattering (LTS) measurements. Emission measurements were performed using an intensified CCD camera. By varying several external parameters such as the amplitude of the input voltage, gas composition, and pressure, the influence of these parameters on the discharge behavior was studied. Results of emission measurements showed that they were in good agreement with similar emission measurements on real PDP cells. LTS measurements were performed for the striated PDP‐like discharge at a pressure of 100 Torr and the results showed clear modulations in both profiles of electron density and electron temperature.     

Settlement detection and impervious surface estimation in the Mekong Delta using optical and SAR remote sensing data

Information about the extent of impervious surface and its rate of development is a valuable indicator of urban growth and environmental quality and thus relevant for a wide range of research related to urban ecosystems. Using SPOT-5 data from 2005 to 2009, impervious surface was estimated at a subpixel level for the area of Can Tho province in the Mekong Delta, based on a Support Vector Regression model. Training data comprised a set of SPOT-5 reflectance values each associated with an individual value of subpixel imperviousness as their respective labels. The latter were obtained on the basis of a land cover map, which in turn was derived from a pansharpened QB subset by means of an object-oriented image classification approach. In addition, by varying different sets of training data in the model building process the spectral interrelationships between the urban land cover classes (water, bare soil, vegetation, and impervious surface) and their effect on the estimation of subpixel imperviousness could be examined. In order to exclude irrelevant areas (natural/undeveloped land) from the impervious surface estimation process, single-polarised TerraSAR-X data were used to delineate settlement areas by an object-oriented image classification approach. Furthermore, a change detection method was applied for the respective time period in order to test the suitability of the approach for the automated detection of structural developments within the urban topography. Settlement areas were correctly identified with overall accuracies between 81% and 94%, whilst the comparison of the modelled impervious estimates to the training values gave an absolute mean error below 15%. The results prove the suitability of the approach for an area-wide but selective mapping and monitoring of impervious surface cover within settlement areas only.     

3D modelling of forest canopy structure for remote sensing simulations in the optical and microwave domains

A detailed 3D structural model of a conifer forest canopy was developed in order to simulate the reflectance (optical) and backscatter (microwave) signals measured remotely. We show it is feasible to model forest canopy scattering using detailed 3D models of tree structure including the location and orientation of individual needles. An existing structural growth model of Scots pine (Pinus sylvestris L.), Treegrow, was modified to simulate observed growth stages of a Scots pine canopy from age 5 to 50 years. The 3D tree models showed close structural agreement with in situ measurements. Needles were added to the structural models according to observed phyllotaxy (distribution). Individual trees were used to generate model canopies, which in turn were used to drive optical and microwave models of canopy scattering. Simulated canopy radiometric response was compared with airborne hyperspectral reflectance data (HyMAP) and airborne synthetic aperture RADAR (ASAR) backscatter data. Model simulations agreed well in general with observations, particularly at optical wavelengths where model simulations of low and high density canopy stands were shown to bracket observations. Relatively small sensitivity of observed reflectance to canopy age was captured reasonably well by the simulations. The choice of needle shape and phyllotaxy was shown to have a significant impact on multiple scattering behaviour at the branch scale. In the microwave domain, simulated backscatter values agreed reasonably well with observations at L-band, less so at X-band. L-band simulated backscatter significantly underestimated observed backscatter at younger canopy ages, probably as a result of inappropriate modelling of soil/understory. It is demonstrated that a combined structural and radiometric modelling approach provides a flexible and powerful method for simulating the remotely sensed signal of a forest canopy in the optical and microwave domains. This is particularly useful for exploring the impact of canopy structure on the resulting signal and also for combined retrievals of forest structural parameters from optical and microwave data.     

Relational and institutional embeddedness of Web‐enabled entrepreneurial networks: case studies of netrepreneurs in China

Drawing from a multidisciplinary literature, we form a theoretical perspective of the social embeddedness of economic activity as interpersonal ties that are formed in relation to the institutions of an economy. From this perspective, we then seek to explain the emergence of networks of micro‐entrepreneurs that conduct their business on the Taobao Web platform in China, and we derive theoretical propositions about the social embeddedness of Web platform‐based economic activity. Two case studies of such networks show how Web platform tools and services create conditions of possibility for developing online business by micro‐entrepreneurs and for overcoming cultural reluctance of economic exchange with strangers. Our research suggests that economic activity on Web platforms is embedded in a mix of virtual and community‐based relations that are shaped by and alter the behavioural norms of a local culture. It also points to the government and the corporate Web platform service provider as important organisational actors enabling the creation of entrepreneurial networks.     

The use of mobile messaging‐based case studies in a pharmacotherapy introduction class in China

This study is to examine the attitudes of students towards the case studies based on mobile messaging in a pharmacotherapy introduction class. Case studies were divided into 4 groups, with 30 pharmacy students each group. Each group was required to share pharmaceutical care plans on WeChat by posting messages. A post‐activity survey was conducted: Over 70% of the students agreed that mobile messaging‐based case studies (MMBC) helped developing skills and knowledge and stimulating additional research and readings. Over 60% of the students felt that MMBC helped understanding others' viewpoints and sharing their experience and knowledge. More than half of the students agreed that MMBC was more convenient than traditional and internet‐based case study. Less than 30% of the students agreed that the interaction with other students was good. The findings reflect the MMBC studies' popularity with students. Recommendations to use MMBC studies include (a) balance the merits, such as expressing opinions clearly and concisely, allowing for collaborative learning, with the drawbacks: distraction and the low quality of interactions; (b) use small groups for case discussion; (c) design a collaborative schedule dividing the discussion into different sections.     

Vocabulary learning by mobile‐assisted authentic content creation and social meaning‐making: two case studies

In recent years, we have witnessed the concomitant rise of communicative and contextualized approaches as well as the paradigmatic development of the mobile‐assisted language learning (MALL) framework in analysing language learning. The focus of MALL research has gradually shifted from content‐based (delivery of learning content through mobile devices) to design‐oriented (authentic and/or social mobile learning activities) study. In this paper, we present two novel case studies of MALL that emphasize learner‐created content. In learning English prepositions and Chinese idioms, respectively, the primary school students used the mobile devices assigned to them on a one‐to‐one basis to take photos in real‐life contexts so as to construct sentences with the newly acquired prepositions or idioms. Subsequently, the learners were voraciously engaged in classroom or online discussion of their semantic constructions, thereby enhancing their understanding of the proper usage of the prepositions or idioms. This work shows the potential of transforming language learning into an authentic seamless learning experience.     

Ambient interaction and situational influence: case studies in public sites

Abstract

An audience's direct physical intervention is widely believed to be instrumental in the field of interactive art. However, this long established expectation faces new challenges through the increasing accessibility of a growing diversity of interactive technologies and ubiquitous smart media. Such innovations are often fully integrated components of interactive public artworks, many of which do not directly involve audiences or individuals as key agents in the functional or aesthetic realisation of the work. Based on three case studies of interactive artworks in public places, this article identifies an important characteristic of interactivity in interactive art, through the largely unexplored concept of “Ambient Interaction” in which artworks are embodied and enacted through environmental conditions and situational influences rather than exclusively through people's intentional and direct physical engagement.     

Evaluating micas in petrologic and metallogenic aspect: I–definitions and structure of the computer program MICA

Micas are significant ferromagnesian minerals in felsic to mafic igneous, metamorphic, and hydrothermal rocks. Because of their considerable potential to reveal the physicochemical conditions of magmas in terms of petrologic and metallogenic aspects, mica chemistry is used extensively in the earth sciences. For example, the composition of phlogopite and biotite can be used to evaluate the intensive thermodynamic parameters of temperature (T, °C), oxygen fugacity (fO₂), and water fugacity (fH₂O) of magmatic rocks. The halogen contents of micas permit the estimation of the fluorine and chlorine fugacities that may be used in understanding the metal transportation and deposition processes in hydrothermal ore deposits. The Mica⁺ computer program has been written to edit and store electron-microprobe or wet-chemical mica analyses. This software calculates structural formulae and shares out the calculated anions into the I, M, T, and A sites. Mica⁺ classifies micas in terms of composition and octahedral site-occupancy. It also calculates the intensive parameters such as fO₂, T, and fH₂O from the composition of biotite in equilibrium with K-feldspar and magnetite. Using the calculated F–OH and Cl–OH exchange systematics and various log ratios (fH₂O/fHF, fH₂O/fHCl, fHCl/fHF, X_Cl/X_OH, X_F/X_OH, X_F/X_Cl) of mica analyses. Mica⁺ gives valuable determinations about the characteristics of hydrothermal fluids associated with alteration and mineralization processes. The program output is generally in the form of screen outputs. However, by using the “Grf” files that come up with this program they can be visualized under the Grapher software both as binary and ternary diagrams. Mica analyses subjected to the Mica⁺ program were calculated on the basis of 22+z positive charges taking into account the procedure by the Commission on New Mineral Names Mica Subcommittee of 1998.