Sunlit Areas Research Articles

An Analysis of Shadow Effects on Spectral Vegetation Indexes Using a Ground-Based Imaging Spectrometer

Sunlit vegetation and shaded vegetation are inseparable parts for most remotely sensed images, and the presence of shadows affects high spatial resolution remote sensing and multiangle remote sensing data. Shadows can lead to either a reduction in or a total loss of information in an image. This can potentially lead to the corruption of biophysical parameters derived from pixel values, such as vegetation indexes (VIs). VIs are widely used in remote sensing inversion applications. If the effects of shadows are not properly accounted for, retrieval may be uncertain when using a VI to calculate vegetation parameters. One of the major reasons that the effects of shadows are easy to be ignored in remote sensing is the spatial resolution of the measurement. High spatial and spectral resolutions are typically difficult to achieve simultaneously, and images that have one tend to not have the other. A ground-based imaging spectrometer brings a turning point to solve this problem as it can obtain both high spatial and high spectral resolutions to obtain feature and shadow images simultaneously. The resolution of the system used here was 1 mm at a height of 1 m, and the spectral resolution was better than 5 nm. For each pixel, the spectral curve of the image was almost a pure-pixel spectral curve, which allowed the differentiation of sunlit and shaded areas. To investigate the effects of shadows on different indexes, 14 hyperspectral VIs were calculated. Moreover, the vegetation fractional coverage calculated using the same 14 VIs was compared. The results show that shadows affect not only each narrowband of a VI but also vegetation parameters.

Evaluation of effect of tree canopy on thermal environment, thermal sensation, and mental state

Greenery is considered an important countermeasure technology that can be used to improve the thermal environment in urban areas. In this study, the effects of environmental factors relating to tree canopies on physiological response and human sensible temperatures were examined. Measurements were analyzed to determine the mutual relationship between the environmental elements of the tree canopy and the physiological response and psychological reaction. In five areas with tree canopies of different forms, located on the Osaka Prefecture University campus, measurements were performed during the hot summer season. The amount of solar radiation in the tree canopy was greatly attenuated in comparison to sunlit locations. In addition, it was determined that the air temperature in the tree canopy was about 1°C lower in sunlit areas. Human thermal load under the tree canopies is closer to neutral than in sunlit places. The blocking of solar radiation greatly affected physiological response. Results of psychological testing confirm the effect of comfort was experienced under tree canopies. However, gloomy impressions were suffered in areas where the leaf area index was large. The fatigue value correlated best with physiological response. It was concluded that the thermal sensation of hot was causing mental fatigue.

Effect of outdoor thermal environment on pedestrians' behavior selecting a shaded area in a humid subtropical region

This study analyzes the effect of microclimatic conditions on pedestrians' behavior in selecting shaded places when standing at the traffic signals in a subtropical region of Nagoya, Japan. On-site microclimatic measurements and unobtrusive observations were performed 18 times in two periods, July to October, 2012, and May to August, 2013, in order to obtain physical data and the number of pedestrians in sunlit and shaded areas. The universal thermal climate index (UTCI) model was adopted for assessing the outdoor thermal environment in the sunlit and shaded places in this study. The average UTCI values in the sunlit and shade areas over the measured periods were 38.0 °C and 29.3 °C, respectively, and the difference was 8.7 °C. The number of pedestrians was hardly influenced by heat environment since the observations were conducted on weekdays, thus, almost all had to go out for their routine tasks or work regardless of the conditions. Male and female pedestrians tended to wear hats and parasols, respectively, in order to avoid excessive heat during the hot season. The analytical results indicate that half of the pedestrians select shaded areas when stopping at the traffic signals in a hot environment over 40 °C in UTCI. Female pedestrians are more careful to protect themselves from solar radiation including ultraviolet rays than males. “Shade Design in the City” will be a critical strategy to improve the safety, comfort, and attraction of cities in a hot environment.

Restoration of shadows in multispectral imagery using surface reflectance relationships with nearby similar areas

The presence of shadows in optical satellite images limits the application of remote-sensing technology. It is important to restore shadow radiance information for improving information extraction from remote-sensing images. Several shadow-restoration methods have been developed using complex statistical relationships between shadowed areas and their nearby sunlit areas. In this study, a simple shadow-restoration approach was proposed based on the surface reflectance equality relationship (RER) under the assumption that the surface reflectance of a feature in the shadowed area is equal to that of the same feature in the nearby sunlit area. This approach reduces the number of parameters, thus reducing the error propagated by the uncertainties of extra parameters. The new RER method was tested with three multispectral images with different shadow features. By comparing RER with the widely used mean and variance transformation, the RER was shown to be capable of restoring the image colours, texture, tone, and brightness of the shadowed areas to a visually satisfactory level. Quantitative analysis suggests that RER can help to restore the reflectance of shadow features accurately and has robust performance for a variety of land-surface types. Moreover, RER can be effectively used to restore the spectral shape information of shadow features, which is particularly important when applying RER to the restoration of multispectral imagery for the purpose of image classification.

Pv layout optimization: String tiling using a multi-objective genetic algorithm

Urban environments present new challenges to the integration of photovoltaic systems onto the building envelope. This study describes a multi-objective genetic algorithm developed for the maximization of the PV electrical production and minimization of relevant system costs, such as wiring, modules and inverter costs. Two case studies are analyzed, featuring a partially shaded rooftop and a vertical facade. The PV layouts suggested by the genetic algorithm outperform the conventional configurations by reducing the cost of produced electricity between 6% and 18%. The optimization results also show that layouts with more but shorter PV strings achieve higher energy yields. However, when compared with longer clustered strings in the most sunlit areas of the surfaces, this results in the doubling of costs.

Glazing solar heat gain analysis and optimization at varying orientations and placements in aspect of distributed radiation at the interior surfaces

This paper aims at introducing a novel methodology to calculate the distribution of incoming solar energy on the internal surfaces of closed spaces with an opening at various orientations and placements. While the incoming diffuse solar radiation and the reflected solar radiation are as usually distributed with the use of absorptance–weighted area ratios the penetrating direct radiation is distributed according to the formed sunlit areas on the interior surfaces. The determination of the sunlit areas into the enclosure is accomplished by forming at each time step a, so-called, “sunlit pattern” with four letter-characters specifying the particular illuminated interior surfaces that are stricken by the sun’s rays. Though this study is carried out for the Mediterranean climatic conditions, the methodology is general and can be applied to other regions. Following this methodology the optimum glazing setup to maximize the solar heat gain per square meter during the heating period is formulated and solved as a constrained optimization problem. To this effect, the well-known pattern search methodology has been appropriately adapted to deal with the highly nonlinear nature of this problem, particularly when the glazing distance from the right sidewall is variable. Representative computer results are provided showing the optimization problem complexity by varying the glazing width to height and the floor width to floor depth ratios.

Sunlit fractions on urban facets – Impact of spatial resolution and approach

The extent of the surface area sunlit is critical for radiative energy exchanges and therefore for a wide range of applications that require urban land surface models (ULSM), ranging from human comfort to weather forecasting. Here a computationally demanding shadow casting algorithm is used to assess the capability of a simple single-layer urban canopy model, which assumes an infinitely long rotating canyon (ILC), to reproduce sunlit areas on roofs, walls and roads over central London. Results indicate that the sunlit road areas are well-represented but somewhat smaller using an ILC, while sunlit roofs areas are consistently larger, especially for dense urban areas. The largest deviations from real world sunlit areas are for roofs during mornings and evenings. Sunlit fractions on walls are overestimated using an ILC during mornings and evenings are found. The implications of these errors are dependent on the application targeted. For example, (independent of albedo) ULSMs used in numerical weather prediction applying ILC representation of the urban form will overestimate outgoing shortwave radiation from roofs due to the overestimation of sunlit fraction of the roofs. Complications of deriving height to width ratios from real world data are also discussed.

Fusing complementary images for pavement cracking measurements

Cracking is a major pavement distress that jeopardizes road serviceability and traffic safety. Automated pavement distress survey (APDS) systems have been developed using digital imaging technology to replace human surveys for more timely and accurate inspections. Most APDS systems require special lighting devices to illuminate pavements and prevent shadows of roadside objects that distort cracks in the image. Most artificial lighting devices are laser based, and are either hazardous to unprotected people or require dedicated power supplies on the vehicle. This study was aimed to develop a new imaging system that can scan pavement surface at highway speed and determine the level of severity of pavement cracking without using any artificial lighting. The new system consists of dual line-scan cameras that are installed side by side to scan the same pavement area as the vehicle moves. Cameras are controlled with different exposure settings so that both sunlit and shadowed areas can be visible in two separate images. The paired images contain complementary details useful for reconstructing an image in which the shadows are eliminated. This paper intends to present (1) the design of the dual line-scan camera system, (2) a new calibration method for line-scan cameras to rectify and register paired images, (3) a customized image-fusion algorithm that merges the multi-exposure images into one shadow-free image for crack detection, and (4) the results of the field tests on a selected road over a long period.

A sun–crown–sensor model and adapted C-correction logic for topographic correction of high resolution forest imagery

Canopy shadowing mediated by topography is an important source of radiometric distortion on remote sensing images of rugged terrain. Topographic correction based on the sun–canopy–sensor (SCS) model significantly improved over those based on the sun–terrain–sensor (STS) model for surfaces with high forest canopy cover, because the SCS model considers and preserves the geotropic nature of trees. The SCS model accounts for sub-pixel canopy shadowing effects and normalizes the sunlit canopy area within a pixel. However, it does not account for mutual shadowing between neighboring pixels. Pixel-to-pixel shadowing is especially apparent for fine resolution satellite images in which individual tree crowns are resolved. This paper proposes a new topographic correction model: the sun–crown–sensor (SCnS) model based on high-resolution satellite imagery (IKONOS) and high-precision LiDAR digital elevation model. An improvement on the C-correction logic with a radiance partitioning method to address the effects of diffuse irradiance is also introduced (SCnS+C). In addition, we incorporate a weighting variable, based on pixel shadow fraction, on the direct and diffuse radiance portions to enhance the retrieval of at-sensor radiance and reflectance of highly shadowed tree pixels and form another variety of SCnS model (SCnS+W). Model evaluation with IKONOS test data showed that the new SCnS model outperformed the STS and SCS models in quantifying the correlation between terrain-regulated illumination factor and at-sensor radiance. Our adapted C-correction logic based on the sun–crown–sensor geometry and radiance partitioning better represented the general additive effects of diffuse radiation than C parameters derived from the STS or SCS models. The weighting factor Wt also significantly enhanced correction results by reducing within-class standard deviation and balancing the mean pixel radiance between sunlit and shaded slopes. We analyzed these improvements with model comparison on the red and near infrared bands. The advantages of SCnS+C and SCnS+W on both bands are expected to facilitate forest classification and change detection applications.

Thermoregulatory Behavior and Fungal Infection ofAnoplophora glabripennis(Coleoptera: Cerambycidae)

Asian longhorned beetles, Anoplophora glabripennis (Motschulsky), are invasive wood borers that are native to China and Korea but have been introduced to North America and Europe. These beetles have great potential to negatively impact economic and environmental interests in hardwood and urban forests if they become established. The entomopathogenic fungus Metarhizium brunneum Petch (previously Metarhizium anisopliae (Metschnikoff) Sorokin) is under development for control of A. glabripennis. Some insect species eliminate pathogens or delay disease progression through thermoregulation. Because Asian longhorned beetles had been observed occupying sunlit areas of the tree canopy, we hypothesized that behavioral fevering could be used to delay mortality of fungal-infected beetles. M. brunneum cultures incubated at 34°C for 5 h/d grew significantly slower compared with cultures incubated at lower temperatures. Holding M. brunneum-infected A. glabripennis at 34°C for 5 h/d significantly delayed mortality by 2 d compared with infected beetles held at ≤31°C. Adult A. glabripennis did not exhibit behavioral fever when infected. Uninfected males, when provided with food, and both uninfected males and females when deprived of food, slightly increased their preferred temperature over time. When held at 15°C before being placed into temperature gradients, uninfected beetles did not increase their temperatures above ambient. Results demonstrate that M. brunneum-infected A. glabripennis do not exhibit behaviors necessary to elevate their body temperatures enough to combat M. brunneum infections through thermoregulation.

Orbit Radial Dynamic Analysis of Two-Craft Coulomb Formation at Libration Points

The linearized orbit radial dynamics and stability analysis of a two-craft virtual Coulomb structure at Earth–moon libration points are investigated. The linearized study assumes that the sunlit areas of the two-craft structure are equal such that the differential solar radiation pressure on the formation is zero. The relative distance between the two satellites of the Coulomb tether is controlled using electrostatic Coulomb forces. The separation distance between the satellites is stabilized with a charge feedback law that maintains the relative distance at a constant value. The electrostatic virtual tether between the two craft is capable of both tensile and compressive forces. The gravity gradient torques on the formation due to the two celestial objects is exploited to stabilize the Coulomb tether formation in the orbit radial direction. Controlling the separation distance stabilizes the in-plane rotation angle; however, the out-of-plane rotational motion is not affected by the spacecraft charge control law. The new two-craft dynamics at the libration points is provided as a general framework in which circular Earth orbit dynamics form a special case. Furthermore, an alternate linear control technique for a two-craft Coulomb virtual tether formation’s radial equilibrium at a collinear libration point is developed and analyzed. Numerical simulations using charge feedback law are presented at both a collinear and a triangular libration point.

Satellite Solar-Panel Occlusion Algorithm Based on OpenCL

The electrical output of solar-panel is affected by the illuminated condition. It is closely related to the sunlight incidence angle and sunlit area of the solar-panel. This paper firstly points out the importance of satellite solar-panel occlusion in aerospace fields，introduces the satellite body model, the solar-panel model, and deduction models such as sunlit area, effective number of battery strings, sunshine incidence angle and so on. This paper presents an algorithm for analyzing satellite solar-panel shadow, and uses OpenCL to improve the efficiency. Finally, the results of this algorithm implemented are analyzed by mathematical simulations.

Mapping shadows in very high-resolution satellite data using HSV and edge detection techniques

Multispectral scanners (MSS) such as IKONOS have very high spatial resolution and therefore, provide excel- lent source of information about terrestrial features. The im- agesfromthesescannersmaycontainshadowsthatcanleadto partial or complete loss of radiometric information, leading to misinterpretation or inaccurate classification. In addition, the identification of shadows is critical for several applications. The goal of this study is to develop computer-based algo- rithms to detect shadows from IKONOS panchromatic (1× 1 m) and MSS bands (4×4 m). We converted subsets of IKONOS pan and MSS images over New York City to HSV color space, and used histogram analysis to determine an intensity threshold. Potential sunlit and shadow areas were demarcated and edge detection techniques were employed to eliminate the non-shadow, low-intensity areas and identify shadow areas on the image subsets. We tested the results on a time series of datasets to develop a robust model that has the capability to detect shadows and extract them from high- resolution satellite imagery.

Characteristics of the mean radiant temperature in high latitude cities—implications for sensitive climate planning applications

Knowledge of how the mean radiant temperature (T mrt ) is affected by factors such as location, climate and urban setting contributes to the practice of climate sensitive planning. This paper examines how T mrt varies within an urban setting and how it is influenced by cloudiness. In addition, variations of T mrt in three high latitude cities are investigated in order to analyse the impact of geographical context and climate conditions. Results showed large spatial variations between sunlit and shaded areas during clear weather conditions, with the highest values of T mrt close to sunlit walls and the lowest values in the areas shaded by buildings and vegetation. As cloudiness increases, the spatial pattern is altered and the differences are reduced. The highest T mrt under cloudy conditions is instead found in open areas where the proportion of shortwave diffuse radiation from the sky vault is high. A regional comparison between three Swedish coastal cities showed that T mrt during summer is similar regardless of latitudinal location. On the other hand, large differences in T mrt during winter were found. Shadows, both from buildings and vegetation are the most effective measure to reduce extreme values of T mrt. However, extensive areas of shadow are usually not desired within outdoor urban environments at high latitude cities. One solution is to create diverse outdoor urban spaces in terms of shadow and also ventilation. This would provide individuals with access to a choice of thermal environments which they can use to assist their thermal regulation, based on personal needs and desires.

The vertical leaf distribution of Ulmus laevis Pall.

Vertical leaf distribution and relative irradiance were ascertained for the dominant species Ulmus laevis Pall. at the level of the individual tree and at the level of the stand in a mixed broad-leaved forest in South Moravia, the Czech Republic. The study consisted of detailed, destructive measurement of five selected sample trees and the establishment of basic biometric parameters for the entire stand. Using allometric relationships, measurements from sample trees were generalized to diameter at breast height (DBH) classes and were then scaled up to the level of the imaginary pure stand of elm; the selected independent variables were tree height and DBH. The vertical leaf distribution was unimodal in trees with smaller dimensions and bimodal in trees with larger dimensions. The leaf area index (LAI) of the stand was 4 (6.4 including the undergrowth), and the sunlit leaf area index (SLAI) was 1.7. Dominant trees had a higher proportion of sunlit leaf area than subdominant and suppressed trees. Determination of appropriate methods and intensity of thinning can lead to optimizing of irradiation control, vitality increase of the elm stands and subsequently to a higher resistance to Dutch elm disease vector and disease itself.

Testing lunar permanently shadowed regions for water ice: LEND results from LRO

We use measurements from the Lunar Exploration Neutron Detector (LEND) collimated sensors during more than one year of the mapping phase of NASA's Lunar Reconnaissance Orbiter (LRO) mission to make estimates of the epithermal neutron flux within known large Permanently Shadowed Regions (PSRs). These are compared with the local neutron background measured outside PSRs in sunlit regions. Individual and collective analyses of PSR properties have been performed. Only three large PSRs, Shoemaker and Cabeus in the south and Rozhdestvensky U in the north, have been found to manifest significant neutron suppression. All other PSRs have much smaller suppression, only a few percent, if at all. Some even display an excess of neutron emission in comparison to the sunlit vicinity around them. Testing PSRs collectively, we have not found any average suppression for them. Only the group of 18 large PSRs, with area >200 km2, show a marginal effect of small average suppression, ∼2%, with low statistical confidence. A ∼2% suppression corresponds to ∼125 ppm of hydrogen taking into account the global neutron suppression near the lunar poles and assuming a homogeneous H distribution in depth in the regolith. This means that all PSRs, except those in Shoemaker, Cabeus and Rozhdestvensky U craters, do not contain any significant amount of hydrogen in comparison with sunlit areas around them at the same latitude.

An SVM Classification of Tree Species Radiometric Signatures Based on the Leica ADS40 Sensor

This paper focuses on the use of multispectral measurements to classify remotely sensed radiance and reflectance information into three tree species, Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) H. Karst.), and birch (Betula pubescens Ehrh., Betula pendula Roth), using a Support Vector Machine (SVM) algorithm. The features used for the classifier are radiometric involving different viewing angles, but without textural information. At-sensor radiance (ASR) signals used here were obtained using a four-band Leica ADS40-SH52 airborne sensor. The experiments were carried out in a forest area at Hyytiala, in southern Finland (61°50' N, 24°20' E), which has been widely used for similar purposes, so that detailed tree-level information has been reported previously. The flight was carried out on August 23, 2008. ADS40 ASR measurements can be converted to ground reflectance signatures in two viewing directions using atmosphere and BRDF modeling implemented in Leica XPro 4.2 software. Taking into account the assumptions entailed in the radiometric model, the classification performance of the ground reflectance is evaluated only for the pixel values under sunlit conditions and is compared with the performance of the ASR data. The sunlit and shaded parts of the tree crown were extracted based on the use of LiDAR data for crown shape modeling. The classification results for the real multispectral measurements are compared with the earlier results obtained with simulated Leica ADS40 at-sensor radiance response values which were based on the ground-level high-resolution ground reflectance factor measurements using a single viewing direction. The simulated classification accuracy was 75-79% with the original four bands, while it was up to 85-88%, using the simulated fifth channel. It was found here that the classification accuracy using comparable real ADS40-SH52 four-band data and one viewing angle was 75-79% and increased to 78-82% with two viewing angles. The results show that the best-case classification accuracy with real data can reach 88% if trees are modeled as objects with sunlit and shaded areas, and multiple measurements are available for every tree. The results suggest that ground reflectance estimation with normalization of anisotropic reflectance behavior leads to similar classification performance to ASR data, but can in some cases improve the generalization properties of training data.

The Effects of Weather on Walking Rates in Nine Cities

This study examined whether locally felt weather had a measurable effect on the amount of walking occurring in a given locale, by examining the observed walking rate in relation to air temperature, sunlight, and precipitation. Web-based cameras in nine cities were used to collect 6,255 observations over 7 months. Walking volumes and levels of precipitation and sunlight were captured by visual inspection; air temperature was obtained from local meteorological stations. A quasi-Poisson regression model to test the relationship between counts of pedestrians and weather conditions revealed that all three weather variables had significant associations with fluctuations in volumes of pedestrians, when controlling for city and elapsed time. A 5°C increase in temperature was associated with a 14% increase in pedestrians. A shift from snow to dry conditions was associated with an increase of 23%, and a 5% increase in sunlit area was associated with a 2% increase.

Urban Energy Balance Obtained from the Comprehensive Outdoor Scale Model Experiment. Part II: Comparisons with Field Data Using an Improved Energy Partition

Abstract The objective of this study is to examine the differences and similarities in the annual trends of the urban surface energy balance (SEB) among long-term field measurements. Four datasets analyzed for the study were collected in the following experiments or observational sites: Comprehensive Outdoor Scale Model experiments (COSMO), the Kugahara site in Tokyo, Japan (Ku04), and the Sperrstrasse and Spalenring sites in Basel, Switzerland (BuU1 and BuU2). A new variable, the forcing radiation QFR, has been proposed to replace the conventional net radiation Q* for the normalization of the SEB components. Here, QFR is defined as the sum of net shortwave radiation and downward longwave radiation. Because QFR does not include the upward longwave radiation, it is independent of the surface temperature, which is determined by the energy partitioning process. Therefore, QFR is independent of the energy partitioning process itself. With the use of QFR, the characteristics of the daytime normalized components of the SEB equation (i.e., upward longwave radiation, QL↑/QFR, turbulence fluxes (QH + QE)/QFR, and heat storage ΔQS/QFR) were investigated. The above energy fluxes normalized by the forcing radiation depended on the friction velocity u*. An increase of u* predominantly enhanced (QH + QE)/QFR and reduced both QL↑/QFR and ΔQS/QFR. When this u* dependency on the SEB was taken into consideration, the annual variations of these three flux ratios from cities located in similar latitudes and longitudes (i.e., BuU1 and BuU2, Ku04, and COSMO) were very similar. At BuU1 and BuU2, QL↑/QFR showed larger seasonal amplitudes than at COSMO and Ku04. The seasonal variations of (QH + QE)/QFR were roughly out of phase with respect to those of QL↑/QFR, resulting in relatively small seasonal variations of ΔQS/QFR. Furthermore, the effects of urban canyon geometry on the SEB were examined by comparing the SEB for the roofs to that for the canyon. The three-dimensional urban canyon geometry enhanced the heat storage efficiency relative to the forcing radiation ΔQS/QFR of the canyon in comparison with that of roofs or flat surfaces. This observation was explained by the continuous movement of sunlit areas on the walls and streets.

Topographic normalization for improving vegetation classification in a mountainous watershed in Northern Thailand

Land cover classifications are adversely affected by shading or topographic effects in mountainous areas in that the spectral properties of an entity in the shade appear to be different from those of the same entity in a sunlit area. Topographic effects can make it especially difficult to distinguish different successional stages of vegetation. The current work uses a simplified topographic normalization method to reduce the topographic effect and to improve land cover classification in a mountainous watershed in northern Thailand. Data used in the study were two Landsat 7 Enhanced Thematic Mapper Plus (ETM+) images acquired on 5 March 2000 and 7 February 2002, a digital elevation model, and Global Positioning Systems (GPS) ground truth data collected in July 2002 consisting of geographic location (latitude/longitude), feature information and ground reference photographs. A supervised land cover classification was conducted on original and normalized images. In general, the classification accuracy of the different successional stages of vegetation was improved in the normalized images.