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1
Bidschadler, R. A., and P. L. Vornberger. "Detailed elevation map of Ice Stream C, Antarctica, using satellite imagery and airborne radar." Annals of Glaciology 20 (1994): 327–35. http://dx.doi.org/10.3189/1994aog20-1-327-335.
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Surface elevations collected by airborne radar arc interpolated between flight lines using Landsat I'M image data to produce a detailed digital elevation model of a part of Ice Stream C, West Antarctica. The photodinometric method developed is general and allows the derivation of surface elevation along any line parallel to the solar illumination from a single known elevation on that line. Accuracies of the derived elevations are improved with additional elevation control that permits an empirical determination of parameters in the photoclinometric equation accounting for albedo and atmospheric scattering. Elevation errors increase approximately linearly with the integration distance. An explicit relationship is derived that shows the image brightness is insensitive to the cross-Sun component of small surface slopes typical of ice sheets. The greatest impediment to the accuracy of this technique is the radiance resolution of the sensor which limits the signal-to-noise ratio of the image data and can mask variations in albedo that are falsely converted to variations in surface slope.
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Bidschadler, R. A., and P. L. Vornberger. "Detailed elevation map of Ice Stream C, Antarctica, using satellite imagery and airborne radar." Annals of Glaciology 20 (1994): 327–35. http://dx.doi.org/10.1017/s0260305500016645.
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Surface elevations collected by airborne radar arc interpolated between flight lines using Landsat I'M image data to produce a detailed digital elevation model of a part of Ice Stream C, West Antarctica. The photodinometric method developed is general and allows the derivation of surface elevation along any line parallel to the solar illumination from a single known elevation on that line. Accuracies of the derived elevations are improved with additional elevation control that permits an empirical determination of parameters in the photoclinometric equation accounting for albedo and atmospheric scattering. Elevation errors increase approximately linearly with the integration distance. An explicit relationship is derived that shows the image brightness is insensitive to the cross-Sun component of small surface slopes typical of ice sheets. The greatest impediment to the accuracy of this technique is the radiance resolution of the sensor which limits the signal-to-noise ratio of the image data and can mask variations in albedo that are falsely converted to variations in surface slope.
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Chen, Y. T., B. H. Lim, and C. S. Lim. "General Sun Tracking Formula for Heliostats With Arbitrarily Oriented Axes." Journal of Solar Energy Engineering 128, no. 2 (June 25, 2005): 245–50. http://dx.doi.org/10.1115/1.2189868.
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The most general form of solar tracking formulae of an arbitrarily oriented heliostat toward an arbitrarily located target on the Earth is presented. With this complete solution, the used azimuth-elevation, spinning-elevation tracking formula, etc., are the special cases of it. Therefore, more application may be sought out for many individual cases in solar engineering. The new form of tracking solution could bring changes in the geometry and structure of the design of heliostat to meet various requirements.
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Chong, K. K., and M. H. Tan. "Comparison Study of Two Different Sun-Tracking Methods in Optical Efficiency of Heliostat Field." International Journal of Photoenergy 2012 (2012): 1–10. http://dx.doi.org/10.1155/2012/908364.
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There are two sun-tracking methods widely used for the heliostat, which are conventional Azimuth-Elevation and revolutionary Spinning-Elevation methods. Following the previous study to compare the range of motion, a comparison study in optical efficiency of heliostat field for the two methods is further explored in this paper. A special algorithm using ray-tracing technique has also been developed to simulate the optical efficiency of heliostat field for both sun-tracking methods in different latitudes. With the new algorithm, comprehensive analysis to compare the optical efficiency of individual heliostat and the overall heliostat field for the two sun-tracking methods has been carried out.
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Huuskonen, Asko, and Iwan Holleman. "Determining Weather Radar Antenna Pointing Using Signals Detected from the Sun at Low Antenna Elevations." Journal of Atmospheric and Oceanic Technology 24, no. 3 (March 1, 2007): 476–83. http://dx.doi.org/10.1175/jtech1978.1.
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Abstract A method to determine the elevation and azimuth biases of the radar antenna using solar signals observed by a scanning radar is presented. Data recorded at low elevation angles where the atmospheric refraction has a significant effect on the propagation of the radio wave are used, and a method to take the effect of the refraction into account in the analysis is presented. A set of equations is given by which the refraction of the radio waves as a function of the relative humidity can easily be calculated. Also, a simplified model for the calculation of the atmospheric attenuation is presented. The consistency of the adopted models for the atmospheric refraction and atmospheric attenuation is confirmed by data collected at a single elevation pointing, but over a long observing time. Finally, the method is applied to datasets based on operational measurements at the Finnish Meteorological Institute (FMI) and Royal Netherlands Meteorological Institute (KNMI), and elevation and azimuth biases of the radars are shown.
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Reimann, Jens, and Martin Hagen. "Antenna Pattern Measurements of Weather Radars Using the Sun and a Point Source." Journal of Atmospheric and Oceanic Technology 33, no. 5 (May 2016): 891–98. http://dx.doi.org/10.1175/jtech-d-15-0185.1.
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AbstractThe sun is known to be a good target for weather radar calibration. In this paper high-resolution raster scans of the sun at high elevations will be used to derive the antenna pattern of weather radar, without being affected by beam propagation effects and reflections close to the earth’s surface. It is shown that this pattern matches well to pattern measurements using a point source. Hence, a good estimation of the real antenna pattern can be derived using the sun.Furthermore, formulas to extract undistorted antenna patterns from the sun, even at high-elevation angles, are derived. The signal processing required to achieve high sensitivity for the antenna pattern measurements will be described. Important parts of the antenna pattern—for example, sidelobes—become visible when using long integration times.The polarimetric receiver channel cross-correlation coefficient is proposed as a figure of merit of the cross-polar isolation of the antenna and hence the cross-polar pattern. The results are also compared to point source measurements. This illustrates how an unpolarized signal source like the sun can be used to derive polarimetric variables.
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Liu, Chao, and Jing Hui. "Research on Physical MPPT of Photovoltaic Array System Based on Image Processing." Applied Mechanics and Materials 321-324 (June 2013): 1138–44. http://dx.doi.org/10.4028/www.scientific.net/amm.321-324.1138.
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Based on analyzing the development and the performance feature of existing solar tracker, we propose a solar Maximum Power Point Tracking (MPPT) strategy which combines photoelectric sensor and image processing. Firstly, photoelectric tracking mode positions the sun in the field of view of the image sensor. Then, the position of the sun image is captured by the image sensor. After that, we can find the coordinates of the sun spot in the field of view through image binarization processing. According to the number of steps of stepper motor rotation which is calculated by the deviation of coordinates, the controller drives the biaxial photosensitive (PV) array tracking device, making the sun spot always fall in the centre of the image. Tests show that the elevation angle and azimuth angle of the tracking range of the photovoltaic array are both 0～270°.The average tracking error of elevation angle is less than 0.7°, and the average tracking error of azimuth angle is less than 0.5°.
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Igoe, D. P., and A. V. Parisi. "Solar current output as a function of sun elevation: students as toolmakers." Physics Education 50, no. 6 (October 2015): 657–61. http://dx.doi.org/10.1088/0031-9120/50/6/657.
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Martha, Tapas R., Norman Kerle, Cees J. van Westen, Victor Jetten, and K. Vinod Kumar. "Effect of Sun Elevation Angle on DSMs Derived from Cartosat-1 Data." Photogrammetric Engineering & Remote Sensing 76, no. 4 (April 1, 2010): 429–38. http://dx.doi.org/10.14358/pers.76.4.429.
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Peart, David R., Matthew B. Jones, and Peter A. Palmiotto. "Winter injury to red spruce at Mount Moosilauke, New Hampshire." Canadian Journal of Forest Research 21, no. 9 (September 1, 1991): 1380–89. http://dx.doi.org/10.1139/x91-195.
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We report the severity and detailed spatial patterns of winter injury to red spruce (Picearubens Sarg.) in the winter of 1988–1989 and assess support for the desiccation and freezing hypotheses. Foliar injury was quantified at three elevations (840, 990, and 1140 m) and on east- and west-facing slopes in the spruce-fir zone at Mount Moosilauke, New Hampshire. Overall, 29% of current-year foliage on red spruce trees was killed by winter injury. Injury increased with elevation. There was a weak tendency for winter injury to be higher on the sun-exposed south sides of crowns, but substantial injury also occurred on shaded foliage. Injury increased markedly with height in crown at high elevation, but decreased with height at low elevation. The results appear inconsistent with desiccation as the main cause of winter injury. Elevational trends in foliar injury are consistent with the freezing hypothesis, but the strong trends in foliar injury by height within trees cannot be fully explained without further data on spatial variation in microclimate and freezing tolerance. Failure to break bud was assessed on the same spatial scales as foliar injury. Bud break was least in trees and crown sections with severe foliar injury. No evidence for winter injury was found on balsam fir (Abiesbalsamea (L.) Mill.). The results support the hypothesis that winter injury may contribute to the current decline of red spruce in the northern Appalachians.
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Wang, Jiang, Yongchao Zhang, Yin Zhang, Yulin Huang, Jianyu Yang, and Yuming Du. "Performance in Solar Orientation Determination for Regular Pyramid Sun Sensors." Sensors 19, no. 6 (March 22, 2019): 1424. http://dx.doi.org/10.3390/s19061424.
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Non-planar sun sensors can determine solar orientation by existing photodiodes or by reusing solar panels, without increasing the size and mass of spacecraft. However, a limiting factor for the improvement of the accuracy of orientation lies in the lack of a detailed performance assessment on interference suppression. In this paper, a new method that determines solar orientation in the frequency domain is developed for regular pyramid sun sensors, which are formed by regular pyramid arrays. Furthermore, two formulations are established to evaluate the errors of the solar azimuth and elevation angle in solar orientation determination based on the newly proposed frequency-domain method. With these formulations of performance evaluation, we discover the mathematical relationship between the interference spectrum, array geometry, solar irradiance, solar azimuth or elevation angle, and the error in solar orientation determination for the first time. This reveals that the internal interference from the detection system can be completely suppressed in solar orientation determination, and the constant interference can be eliminated in the estimation of solar azimuth angle. Simulation and field experiments validated the effectiveness of the new orientation method, error formulations and performance of each interference source.
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Horton, S., M. Schirmer, and B. Jamieson. "Meteorological, elevation, and slope effects on surface hoar formation." Cryosphere Discussions 9, no. 2 (March 23, 2015): 1857–85. http://dx.doi.org/10.5194/tcd-9-1857-2015.
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Abstract. Failure in layers of buried surface hoar crystals (frost) can cause hazardous snow slab avalanches. Surface hoar crystals form on the snow surface and are sensitive to micro-meteorological conditions. In this study, the role of meteorological and terrain factors were investigated for three surface hoar layers in the Columbia Mountains of Canada. The distribution of crystals was observed over different elevations and aspects during 20 days of field observations. The same layers were modelled on a 2.5 km horizontal grid by forcing the snow cover model SNOWPACK with forecast weather data from a numerical weather prediction model. The moisture content of the air (i.e. absolute humidity) had the largest impact on modelled surface hoar growth, with warm and moist air being favourable. Surface hoar was most developed at certain elevation bands, usually corresponding to elevations with warm humid air, light winds, and cold surface temperatures. SNOWPACK simulations on virtual slopes systematically predicted smaller surface hoar on south-facing slopes. In the field, a complex combination of surface hoar and sun crusts were observed, suggesting the model did not adequately resolve the surface energy balance on slopes. Overall, a coupled weather–snow cover model could benefit avalanche forecasters by predicting surface hoar layers on a regional scale over different elevation bands.
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Száz, Dénes, Alexandra Farkas, András Barta, Balázs Kretzer, Ádám Egri, and Gábor Horváth. "North error estimation based on solar elevation errors in the third step of sky-polarimetric Viking navigation." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 472, no. 2191 (July 2016): 20160171. http://dx.doi.org/10.1098/rspa.2016.0171.
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The theory of sky-polarimetric Viking navigation has been widely accepted for decades without any information about the accuracy of this method. Previously, we have measured the accuracy of the first and second steps of this navigation method in psychophysical laboratory and planetarium experiments. Now, we have tested the accuracy of the third step in a planetarium experiment, assuming that the first and second steps are errorless. Using the fists of their outstretched arms, 10 test persons had to estimate the elevation angles (measured in numbers of fists and fingers) of black dots (representing the position of the occluded Sun) projected onto the planetarium dome. The test persons performed 2400 elevation estimations, 48% of which were more accurate than ±1°. We selected three test persons with the (i) largest and (ii) smallest elevation errors and (iii) highest standard deviation of the elevation error. From the errors of these three persons, we calculated their error function, from which the North errors (the angles with which they deviated from the geographical North) were determined for summer solstice and spring equinox, two specific dates of the Viking sailing period. The range of possible North errors Δ ω N was the lowest and highest at low and high solar elevations, respectively. At high elevations, the maximal Δ ω N was 35.6° and 73.7° at summer solstice and 23.8° and 43.9° at spring equinox for the best and worst test person (navigator), respectively. Thus, the best navigator was twice as good as the worst one. At solstice and equinox, high elevations occur the most frequently during the day, thus high North errors could occur more frequently than expected before. According to our findings, the ideal periods for sky-polarimetric Viking navigation are immediately after sunrise and before sunset, because the North errors are the lowest at low solar elevations.
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Ionov, Pavel I., and Andrew K. Mollner. "Aerosol Optical Thickness Measurement with Elevation-Scanning Lidar." Journal of Atmospheric and Oceanic Technology 32, no. 7 (July 2015): 1364–71. http://dx.doi.org/10.1175/jtech-d-14-00183.1.
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AbstractHigh-accuracy measurement of aerosol optical thickness (AOT) τa with an elevation-scanning lidar is demonstrated and the results are compared with a collocated Cimel 318 sun photometer. Linear regression of the time-coincident data from a 2-week measurement campaign with the two instruments is found to be τalidar = (1.00 ± 0.17)τaphot + (0.025 ± 0.019) (1σ). The method proved to have sufficient accuracy to measure AOTs of 0.1–0.2 commonly seen in relatively clear atmosphere. The measurement is absolute and thus does not depend on any external calibration standards.
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Aoyama, Hiroyuki, and Yuichi Nakajo. "D114 A Panel Type Solar Cooker for the Areas with Low Sun Elevation." Proceedings of the National Symposium on Power and Energy Systems 2008.13 (2008): 175–78. http://dx.doi.org/10.1299/jsmepes.2008.13.175.
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Lazarus, Brynne E., Paul G. Schaberg, Gary J. Hawley, and Donald H. DeHayes. "Landscape-scale spatial patterns of winter injury to red spruce foliage in a year of heavy region-wide injury." Canadian Journal of Forest Research 36, no. 1 (January 1, 2006): 142–52. http://dx.doi.org/10.1139/x05-236.
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Red spruce (Picea rubens Sarg.) winter injury is caused by freezing damage that results in the abscission of the most recent foliar age-class. Injury was widespread and severe in the northeastern United States in 2003 and was assessed at multiple elevations at 23 sites in Vermont and adjacent states. This paper presents a spatial analysis of these injury assessments. Relationships between winter injury on dominant and codominant spruce trees and elevation, latitude, longitude, slope, and aspect were investigated with least squares regression and geographically weighted regression. Results of these analyses indicate that injury increased (1) with elevation; (2) from east to west; (3) with the degree to which plots faced west, except at the highest elevations, where injury was uniformly severe; (4) with increases in slope steepness at higher elevations, or with decreases in slope steepness at lower elevations; and (5) with the degree to which plots faced south, except at the highest elevations in northern locations, where injury was uniformly severe. Because injury was greater in areas that have historically received higher levels of acid and nitrogen deposition western portions of the study region, west-facing slopes, and higher elevations observed patterns of injury support the hypothesis that acidic and (or) nitrogen deposition act on a landscape scale to exacerbate winter injury. Greater injury on south-facing slopes suggests that sun exposure exacerbates injury or its expression.
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Horton, S., M. Schirmer, and B. Jamieson. "Meteorological, elevation, and slope effects on surface hoar formation." Cryosphere 9, no. 4 (August 7, 2015): 1523–33. http://dx.doi.org/10.5194/tc-9-1523-2015.
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Abstract. Failure in layers of buried surface hoar crystals (frost) can cause hazardous snow slab avalanches. Surface hoar crystals form on the snow surface and are sensitive to micro-meteorological conditions. In this study, the role of meteorological and terrain factors was investigated for three layers of surface hoar in the Columbia Mountains of Canada. The distribution of crystals over different elevations and aspects was observed on 20 days of field observations during a period of high pressure. The same layers were modelled over simplified terrain on a 2.5 km horizontal grid by forcing the snow cover model SNOWPACK with forecast weather data from a numerical weather prediction model. Modelled surface hoar growth was associated with warm air temperatures, high humidity, cold surface temperatures, and low wind speeds. Surface hoar was most developed in regions and elevation bands where these conditions existed, although strong winds at high elevations caused some model discrepancies. SNOWPACK simulations on virtual slopes systematically predicted smaller surface hoar on south-facing slopes. In the field, a complex combination of surface hoar and sun crusts were observed, suggesting the simplified model did not adequately resolve the surface energy balance on slopes. Overall, a coupled weather–snow cover model could benefit avalanche forecasters by predicting surface hoar layers on a regional scale over different elevation bands.
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Száz, Dénes, Alexandra Farkas, András Barta, Balázs Kretzer, Miklós Blahó, Ádám Egri, Gyula Szabó, and Gábor Horváth. "Accuracy of the hypothetical sky-polarimetric Viking navigation versus sky conditions: revealing solar elevations and cloudinesses favourable for this navigation method." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, no. 2205 (September 2017): 20170358. http://dx.doi.org/10.1098/rspa.2017.0358.
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According to Thorkild Ramskou's theory proposed in 1967, under overcast and foggy skies, Viking seafarers might have used skylight polarization analysed with special crystals called sunstones to determine the position of the invisible Sun. After finding the occluded Sun with sunstones, its elevation angle had to be measured and its shadow had to be projected onto the horizontal surface of a sun compass. According to Ramskou's theory, these sunstones might have been birefringent calcite or dichroic cordierite or tourmaline crystals working as polarizers. It has frequently been claimed that this method might have been suitable for navigation even in cloudy weather. This hypothesis has been accepted and frequently cited for decades without any experimental support. In this work, we determined the accuracy of this hypothetical sky-polarimetric Viking navigation for 1080 different sky situations characterized by solar elevation θ and cloudiness ρ , the sky polarization patterns of which were measured by full-sky imaging polarimetry. We used the earlier measured uncertainty functions of the navigation steps 1, 2 and 3 for calcite, cordierite and tourmaline sunstone crystals, respectively, and the newly measured uncertainty function of step 4 presented here. As a result, we revealed the meteorological conditions under which Vikings could have used this hypothetical navigation method. We determined the solar elevations at which the navigation uncertainties are minimal at summer solstice and spring equinox for all three sunstone types. On average, calcite sunstone ensures a more accurate sky-polarimetric navigation than tourmaline and cordierite. However, in some special cases (generally at 35° ≤ θ ≤ 40°, 1 okta ≤ ρ ≤ 6 oktas for summer solstice, and at 20° ≤ θ ≤ 25°, 0 okta ≤ ρ ≤ 4 oktas for spring equinox), the use of tourmaline and cordierite results in smaller navigation uncertainties than that of calcite. Generally, under clear or less cloudy skies, the sky-polarimetric navigation is more accurate, but at low solar elevations its accuracy remains relatively large even at high cloudiness. For a given ρ , the absolute value of averaged peak North uncertainties dramatically decreases with increasing θ until the sign (±) change of these uncertainties. For a given θ , this absolute value can either decrease or increase with increasing ρ . The most advantageous sky situations for this navigation method are at summer solstice when the solar elevation and cloudiness are 35° ≤ θ ≤ 40° and 2 oktas ≤ ρ ≤ 3 oktas.
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Zhen, Cheng Gang, and Guo Jie Lu. "Research on Embedded Sun-Tracking Control System Based on GPS." Advanced Materials Research 512-515 (May 2012): 267–70. http://dx.doi.org/10.4028/www.scientific.net/amr.512-515.267.
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To improve the efficiency of the power generation，the scheme of the solar tracking system is designed by analyzing the technical characteristics of the GPS positioning system. The microcontroller is chosen as the core which has realized the initiative sun-tracking to improve the efficiency of the power generation. The solar elevation angle and azimuth are calculated by extracting the GPS real-time datas. The position of the solar panels can be obtained through the angle sensor. Finally, adjust the orientation of the panels by the driving stepping motor to track the sun.
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KOROTKOV, A. L., M. P. ENGLISH, G. S. TUCKER, E. PASCALE, and N. GANDILO. "A PINHOLE SUN SENSOR FOR BALLOON-BORNE EXPERIMENT ATTITUDE DETERMINATION." Journal of Astronomical Instrumentation 02, no. 01 (September 2013): 1350005. http://dx.doi.org/10.1142/s2251171713500050.
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We report on the design, calibration and in-flight performance of a sun sensor, which is used to determine the attitude of a balloon-borne telescope. The device uses a position-sensitive detector (PSD) in a pinhole camera. By determining the position of the image of the Sun on the PSD, the orientation of the sun sensor and the boresight of the telescope relative to the Sun can be determined. The pinhole sun sensor (PSS) was first flown in the December 2010 flight of the Balloon-borne Large Aperture Submillimeter Telescope with Polarization (BLAST-Pol). In flight the PSS achieved an accuracy (combined azimuth and elevation) of about 0.18°. The accuracy could be improved by increasing the distance between the pinhole and the PSD, but the field-of-view of the PSS would be reduced.
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Alwan, Ahmed, Ahmed Hameed, and Nuha Hamad. "Analyzing of UV Index with the Time Variation for Baghdad." Iraqi Journal of Industrial Research 8, no. 1 (June 14, 2021): 50–54. http://dx.doi.org/10.53523/ijoirvol8i1id32.
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In order to better realize the effects of UV index (UVI) reaching the earth surface, measurements of effective UVI were carried out during the period of one year over Baghdad; (Lat.33.32- Long.44.45), which receives highly amounts of annual solar radiation. A daily data analysis of UVI is found to reach the highest value during summer reaching the value of 11, and a minimum in winter with the value of 1. A relation between UV index and the solar zenith angle was also, it is found that the UVI is highly dependent on the sun elevation where the atmospheric optical path becomes shorter as sun elevation heighten. It can be concluded that Baghdad city exposure to higher amounts of UVI during summer and several hedges must be taken to avoid health harm implications.
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Howard, Rosie, and Roland Stull. "Forecasting Sun versus Shade in Complex Terrain for the 2010 Winter Olympic and Paralympic Games." Bulletin of the American Meteorological Society 92, no. 10 (October 1, 2011): 1303–9. http://dx.doi.org/10.1175/2011bams-d-11-00017.1.
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During the 2010 Vancouver Winter Olympic and Paralympic Games in Canada, there were 10 mostly sunny days at the outdoor Olympic venues. The warmth and sunshine, possibly a result of El Niño conditions at the time, significantly reduced snow cover at one venue and weakened the snowpack at the other two venues, much to the chagrin of the event organizers. Solar radiation affects ski racing via its effect on snow-surface friction, abrasion, and mechanical strength. Ski technicians and athletes compensate via the choice of ski and wax. For these reasons, sun-versus-shade forecasts were produced for Canadian ski and snowboard teams. A theodolite was used to survey the horizon elevation angles around the full azimuth circles at 133 locations spaced roughly 150 m apart along race pistes (compacted ski runs) at three Olympic venues. This survey was important for including the shadowing effects of the tall evergreen trees that border the pistes. This would not be properly accounted for if only digital elevation data were used. These data, along with the astronomical equations for solar elevation and azimuth, were used to calculate whether each survey point would be in the sun or the shade in cloudless conditions for any time and date during the Olympics. Half-hourly output was provided to ski and snowboard technicians and coaches via a graphical user interface delivered on the Internet.
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Li, Hong Yan, and Zhe Liu. "Design of a New GPS-Based Automatic Sun Tracking Control System." Advanced Materials Research 546-547 (July 2012): 987–91. http://dx.doi.org/10.4028/www.scientific.net/amr.546-547.987.
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A key issue of the solar system is how to determine real-time position of the sun. This paper describes a new solar lighting system. The system uses a new GPS-based solar tracking control module. A Global Positioning System (GPS) is used to acquire latitude, longitude and the current time of the observation point. Single Chip Microcomputer Atmega168 is used to calculate the elevation angle and azimuth of the sun at this time, and to control the stepper motor rotating pan-tilt.. Using the angular position detector as a calibration device, the control system achieves accurate tracking of the sun, and is calibrated to achieve 0.5°accuracy.
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Chen, Y. T., A. Kribus, B. H. Lim, C. S. Lim, K. K. Chong, J. Karni, R. Buck, A. Pfahl, and T. P. Bligh. "Comparison of Two Sun Tracking Methods in the Application of a Heliostat Field." Journal of Solar Energy Engineering 126, no. 1 (February 1, 2004): 638–44. http://dx.doi.org/10.1115/1.1634583.
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The basic mathematics and structure of heliostat have remained unchanged for many decades. Following the challenge first made by Ries et al., the non-imaging focusing heliostat recently proposed by Chen et al. provides an alternative in the field of concentrated solar energy. This paper investigates the performance of a heliostat field composed of the newly proposed heliostats. In contrast to the dynamic curvature adjustment proposed in our previous work for a solar furnace, a fixed asymmetric curvature is used here with the spinning-elevation tracking method. This restriction is intended to equalize the manufacture cost of the new heliostat with that of traditional heliostats with azimuth-elevation tracking and spherical curvature. Fixing the curvature results in only partial aberration correction, compared to full correction using the dynamic adjustment of curvature. Nevertheless, the case studies presented in this paper show that the new heliostat design can reduce the receiver spillage loss by 10–30%, and provide a much more uniform performance without large variations with time of day.
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Tomanová, Helena, and Lucie Pokorná. "The effect of sun elevation, cloudiness, and altitude on the ultraviolet index in Czechia." Geografie 126, no. 2 (2021): 221–42. http://dx.doi.org/10.37040/geografie.2021.001.
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Ultraviolet (UV) radiation has recently become an important topic in relation to the loss of stratospheric ozone. High doses of UV radiation have a negative effect on many organisms. This paper focuses on the UV index (UVI), which expresses the risk of UV radiation on human health. The aim of the paper is to describe the definition of UVI, and its measurement, and to summarize geographical parameters and meteorological conditions affecting the values of UVI. The effect of sun elevation, cloudiness, and altitude is demonstrated using observed data from the Hradec Králové, Košetice and Labská bouda stations during the period 2011–2017. The results show a strong effect of both sun elevation and cloudiness. The highest values of UVI (up to 8) are generally observed on sunny days around midday from May to July. The reduction of the UVI caused by clouds, fog, and rain is, on average, 85% of values typical for sunny days. The effect of altitude is distinctly weaker; a rise of UVI with increasing altitude is 0.4 per 1 km for clear sky and the surface without snow cover.
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Montesano, Paul M., Christopher Neigh, Guoqing Sun, Laura Duncanson, Jamon Van Den Hoek, and K. Jon Ranson. "The use of sun elevation angle for stereogrammetric boreal forest height in open canopies." Remote Sensing of Environment 196 (July 2017): 76–88. http://dx.doi.org/10.1016/j.rse.2017.04.024.
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Apaolaza-Pagoaga, Xabier, Atul A. Sagade, Celestino Rodrigues Ruivo, and Antonio Carrillo-Andrés. "Performance of solar funnel cookers using intermediate temperature test load under low sun elevation." Solar Energy 225 (September 2021): 978–1000. http://dx.doi.org/10.1016/j.solener.2021.08.006.
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Porter, John N., Antony Clarke, Jeffrey S. Reid, Elizabeth A. Reid, Glen Shaw, Hal Maring, and David Kress. "Handheld Sun Photometer Measurements from Light Aircraft*." Journal of Atmospheric and Oceanic Technology 24, no. 9 (September 1, 2007): 1588–97. http://dx.doi.org/10.1175/jtech2087.1.
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Abstract Handheld sun photometers are typically used to make aerosol optical depth measurements while on the ground. Various investigators, in unrelated efforts, have used handheld sun photometers to make aerosol optical depth measurements from light aircraft, but the strengths and weakness of this approach have not been characterized until now. While the ease and relatively low cost of an aircraft manual sun photometer are attractive, determining if the sun photometer was correctly pointed at the sun for each measurement is the biggest challenge. This problem can be partially addressed by collecting a large number of measurements at each altitude, then manually removing the largest optical depths (misalignment always results in erroneous larger values). Examples of past aircraft manual sun photometer measurements are demonstrating that it is possible to obtain quantitative measurements if sufficient sun photometer measurements are made at each elevation. In order to improve on manual sun photometer measurements, a small webcam was attached to the side of a Microtops sun photometer, and the Microtops sun photometer was triggered by computer control. By detecting the position of the sun in the webcam image, it is possible to determine whether the sun photometer was pointed at the sun correctly when the aerosol optical depth measurement was made. Unfortunately, it was found that the Microtops sun photometer takes ∼1.1 s to scan over the five wavelength channels. This 1.1-s delay proved to be too long, preventing the proposed approach from working as the aircraft was bouncing around.
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Chiang, Camilo, Jorunn E. Olsen, David Basler, Daniel Bånkestad, and Günter Hoch. "Latitude and Weather Influences on Sun Light Quality and the Relationship to Tree Growth." Forests 10, no. 8 (July 24, 2019): 610. http://dx.doi.org/10.3390/f10080610.
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Natural changes in photoperiod, light quantity, and quality play a key role in plant signaling, enabling daily and seasonal adjustment of growth and development. Growing concern about the global climate crisis together with scattered reports about the interactive effects of temperature and light parameters on plants necessitates more detailed information about these effects. Furthermore, the actual light emitting diode (LED) lighting technology allows mimicking of light climate scenarios more similar to natural conditions, but to fully exploit this in plant cultivation, easy-to-apply knowledge about the natural variation in light quantity and spectral distribution is required. Here, we aimed to provide detailed information about short and long-term variation in the natural light climate, by recording the light quantity and quality at an open site in Switzerland every minute for a whole year, and to analyze its relationship to a set of previous tree seedling growth experiments. Changes in the spectral composition as a function of solar elevation angle and weather conditions were analyzed. At a solar elevation angle lower than 20°, the weather conditions have a significant effect on the proportions of blue (B) and red (R) light, whereas the proportion of green (G) light is almost constant. At a low solar elevation, the red to far red (R:FR) ratio fluctuates between 0.8 in cloudy conditions and 1.3 on sunny days. As the duration of periods with low solar angles increases with increasing latitude, an analysis of previous experiments on tree seedlings shows that the effect of the R:FR ratio correlates with the responses of plants from different latitudes to light quality. We suggest an evolutionary adaptation where growth in seedlings of selected tree species from high latitudes is more dependent on detection of light quantity of specific light qualities than in such seedlings originating from lower latitudes.
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Toledano, Carlos, Ramiro González, David Fuertes, Emilio Cuevas, Thomas F. Eck, Stelios Kazadzis, Natalia Kouremeti, et al. "Assessment of Sun photometer Langley calibration at the high-elevation sites Mauna Loa and Izaña." Atmospheric Chemistry and Physics 18, no. 19 (October 11, 2018): 14555–67. http://dx.doi.org/10.5194/acp-18-14555-2018.
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Abstract. The aim of this paper is to analyze the suitability of the high-mountain stations Mauna Loa and Izaña for Langley plot calibration of Sun photometers. Thus the aerosol optical depth (AOD) characteristics and seasonality, as well as the cloudiness, have been investigated in order to provide a robust estimation of the calibration uncertainty as well as the number of days that are suitable for Langley calibrations. The data used for the investigations belong to the AERONET and GAW-PFR networks, which maintain reference Sun photometers at these stations with long measurement records: 22 years at Mauna Loa and 15 years at Izaña. In terms of clear-sky and stable aerosol conditions, Mauna Loa (3397 m a.s.l.) exhibits on average 377 Langley plots (243 morning and 134 afternoon) per year suitable for Langley plot calibration, whereas Izaña (2373 m a.s.l.) shows 343 Langley plots (187 morning and 155 afternoon) per year. The background AOD (500 nm) values, on days that are favorable for Langley calibrations, are in the range 0.01–0.02 throughout the year, with well-defined seasonality that exhibits a spring maximum at both stations plus a slight summer increase at Izaña. The statistical analysis of the long-term determination of extraterrestrial signals yields to a calibration uncertainty of ∼ 0.25–0.5 %, this uncertainty being smaller in the visible and near-infrared wavelengths and larger in the ultraviolet wavelengths. This is due to atmospheric variability produced by changes in several factors, mainly the AOD. The uncertainty cannot be reduced based only on quality criteria of individual Langley plots and averaging over several days is shown to reduce the uncertainty to the needed levels for reference Sun photometers.
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Lu, Qi Rong, Lei Wang, Qi Lin Tang, and Yu Jian Yang. "The New Method of Solar Power Generation Using Spin Angle and Elevation Angle Program Control with LabVIEW." Advanced Materials Research 756-759 (September 2013): 650–54. http://dx.doi.org/10.4028/www.scientific.net/amr.756-759.650.
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In order to reduce the power consumption of traditional tracking control, this article according to the tracking theory of spin new angle of elevation design of high precision two-axis solar tracking controller based on LabVIEW programming. The main method of control mode to calculate the position of the sun, using the S1337-1010BQ sensor to track the sun angle deviation automatic proofreading. According to the light intensity automatically adjust the reset program, can maximize the more light. After the test, a new tracking method tracking error is reduced, the photovoltaic efficiency is further improved.
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CÉSPEDES, LAURA N., and NICHOLAS J. BAYLY. "Over-winter ecology and relative density of Canada Warbler Cardellina canadensis in Colombia: the basis for defining conservation priorities for a sharply declining long-distance migrant." Bird Conservation International 29, no. 2 (September 25, 2018): 232–48. http://dx.doi.org/10.1017/s0959270918000229.
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SummaryThe Canada Warbler Cardellina canadensis is a steeply declining Neotropical migratory bird and > 50% of its non-breeding range is within the Colombian Andes. Despite being an abundant migrant in Andean forests, the species’ elevational distribution and non-breeding ecology have yet to be studied, thereby precluding the design of effective conservation actions. During four non-breeding periods (2012–2016), we surveyed Colombia’s three Andean ranges, carrying out passive 5-minute point counts between 700 and 3,150 m asl in five habitats (mature forest, secondary growth, forest edges/riparian forest, shade coffee, sun coffee), recording the perpendicular distance, sex, foraging height, and association with mixed species flocks of Canada Warbler. Habitat variables were recorded at each point. Based on 819 passive point counts, Canada Warblers occupied elevations between 750 and 2,300 m, being more abundant between 1,000 and 2,200 m. Relative densities were higher in mature forest compared to shade coffee and secondary forest, and accordingly abundance increased with canopy height. There was no evidence for a difference in elevation or habitat use by males and females. Within forests, birds foraged at mid-levels, 5–15 m above the ground, and the probability of Canada Warblers occurring in mixed species flocks increased with elevation. Models of variation in relative density throughout the Eastern Andes showed a positive relation with cloud cover and above-ground forest biomass, implying a preference for humid, forested regions. Of the areas in the Eastern Andes with high predicted relative density, ∼ 14% overlapped with protected areas and we identify priority areas where protective measures could benefit the conservation status of the species. For maximum effectiveness, conservation actions should focus on protecting forest fragments and initiating reforestation projects at mid-elevations (1,000–2,200 m), as well as supporting agroforestry practices in humid regions of the Colombian Andes.
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Horváth, Gábor, Péter Takács, Balázs Kretzer, Szilvia Szilasi, Dénes Száz, Alexandra Farkas, and András Barta. "Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions." Royal Society Open Science 4, no. 2 (February 2017): 160688. http://dx.doi.org/10.1098/rsos.160688.
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If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d * for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d > d * is satisfied. Using full-sky imaging polarimetry, we measured the d -pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ . From the measured d -patterns of a given sky we determined the proportion P of the sky for which d > d *. We obtained that P is the largest at low solar elevations θ ≈ 0° and under totally or nearly clear skies with cloud coverage ρ = 0%, when the sun's position is already easily determined. If the sun is below the horizon (−5° ≤ θ < 0°) during twilight, P = 76.17 ± 4.18% for d min ∗ = 23 % under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes.
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Altube, Patricia, Joan Bech, Oriol Argemí, Tomeu Rigo, and Nicolau Pineda. "Intercomparison and Potential Synergies of Three Methods for Weather Radar Antenna Pointing Assessment." Journal of Atmospheric and Oceanic Technology 33, no. 2 (February 2016): 331–43. http://dx.doi.org/10.1175/jtech-d-15-0075.1.
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AbstractThree methods for estimation of the weather radar antenna azimuth and elevation pointing offsets are compared. Two of the methods reviewed use the known location of the sun as a reference. The first of these methods is based on an offline scan of the sun disk. The second method detects and characterizes solar interferences in operative scans. The third method consists of correlating measured ground clutter echoes with echoes simulated using a high-resolution digital elevation model. The main objectives are to review the characteristics in each case, studying their performance in actual operative conditions, and to examine the reasons for the discrepancies between the reported pointing bias estimates, with the aim of laying the groundwork for an optimized individual or combined application and interpretation of the methods. Daily pointing biases estimated through the sun-scanning procedure in a dedicated one-month, short-term campaign are the base for the intercomparison. When applied to the three weather radars operated by the Meteorological Service of Catalonia, the short-term study reveals the advantages and limitations of the methods. A one-year, long-term analysis serves to confirm and clarify the discrepancies inferred from the short-term study and highlights how the antenna position at the time of the measurement may influence the pointing bias estimates. Based on the long-term results, a combination of the two sun-based methods for detection and simultaneous quantification of the pointing bias and the system leveling error is discussed.
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Bramstedt, K., S. Noël, H. Bovensmann, M. Gottwald, and J. P. Burrows. "Precise pointing knowledge for SCIAMACHY solar occultation measurements." Atmospheric Measurement Techniques 5, no. 11 (November 27, 2012): 2867–80. http://dx.doi.org/10.5194/amt-5-2867-2012.
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Abstract. We present a method to precisely determine the viewing direction for solar occultation instruments from scans over the solar disk. Basic idea is the fit of the maximum intensity during the scan, which corresponds to the center of the solar disk in the scanning direction. We apply this method to the solar occultation measurements of the satellite instrument SCIAMACHY, which scans the Sun in elevation direction. The achieved mean precision is 0.46 mdeg, which corresponds to an tangent height error of about 26 m for individual occultation sequences. The deviation of the derived elevation angle from the geolocation information given along with the product has a seasonal cycle with an amplitude of 2.26 mdeg, which is in tangent height an amplitude of about 127 m. The mean elevation angle offset is −4.41 mdeg (249 m). SCIAMACHY's sun follower device controls the azimuth viewing direction during the occultation measurements. The derived mean azimuth direction has an standard error of 0.65 mdeg, which is about 36 m in horizontal direction at the tangent point. We observe also a seasonal cycle of the azimuth mispointing with an amplitude of 2.3 mdeg, which is slightly increasing with time. The almost constant mean offset is 88 mdeg, which is about 5.0 km horizontal offset at the tangent point.
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Oon, Li-Voon, Ming-Hui Tan, Chee-Woon Wong, and Kok-Keong Chong. "Optimization study of solar farm layout for concentrator photovoltaic system on azimuth-elevation sun-tracker." Solar Energy 204 (July 2020): 726–37. http://dx.doi.org/10.1016/j.solener.2020.05.032.
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Tognon, G., S. Ferrari, L. Penasa, F. La Forgia, M. Massironi, G. Naletto, M. Lazzarin, et al. "Spectrophotometric variegation of the layering in comet 67P/Churyumov-Gerasimenko as seen by OSIRIS." Astronomy & Astrophysics 630 (September 20, 2019): A16. http://dx.doi.org/10.1051/0004-6361/201834884.
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Context. Between August 2014 and September 2016, the ESA space mission Rosetta escorted comet 67P/Churyumov-Gerasimenko (67P) during its perihelion passage. The onboard OSIRIS Narrow Angle Camera (NAC) acquired high-resolution multispectral images of the cometary surface. These datasets allowed a characterization of the spectrophotometric variegation of the layering of the large lobe, correlated with the layer structural elevation. Aims. We perform a spectrophotometric characterization of the outcropping stratification of the small lobe of 67P as a function of its structural elevation, and consequently, a spectrophotometric comparison of the layered outcrops of the two lobes. Methods. We selected two sequences of post-perihelion OSIRIS NAC images (~2.4 au outbound tothe Sun), from which we built up two multispectral images, framing an extended geological section of the onion-like stratification of the small lobe. Then we classified the consolidated areas of the outcropping and the relative coarse deposits that were identified in the multispectral data with a two-class maximum likelihood method. For this, we defined the classes as a function of the structural elevation of the surface. Results. As a result, we identified a brightness variegation of the surface reflectance that is correlated with the structural elevation. The outer class, which is located at higher elevations, appears darker than the inner class. This fits previously obtained results for the large lobe. The reflectance values of the nucleus of 67P tend to decrease with increasing structural elevation. Conclusions. The observed spectrophotometric variegation can be due to a different texture as well as to a different content of volatiles and refractories. We suggest that the outer outcrops appear darker because they have been exposed longer, and the inner outcrops appear brighter because the surface has been more effectively rejuvenated. We interpret this variegation as the result of an evolutionary process.
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Bramstedt, K., S. Noël, H. Bovensmann, M. Gottwald, and J. P. Burrows. "Precise pointing knowledge for SCIAMACHY solar occultation measurements." Atmospheric Measurement Techniques Discussions 5, no. 3 (May 31, 2012): 3797–835. http://dx.doi.org/10.5194/amtd-5-3797-2012.
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Abstract. We present a method to precisely determine the viewing direction for solar occultation instruments from scans over the solar disk . Basic idea is the fit of the maximum intensity during the scan, which corresponds to the center of the solar disk in the scanning direction. We apply this method to the solar occultation measurements of the satellite instrument SCIAMACHY, which scans the sun in elevation direction. The achieved precision is in most case below 0.6 mdeg, which corresponds to an tangent height error of about 34 m for individual occultation sequences. The deviation of the derived elevation angle from the geolocation information given along with the product has a seasonal cycle with an amplitude of 2.02 mdeg, which is in tangent height an amplitude of about 114 m. The mean elevation angle offset is −4.7 mdeg (266 m). SCIAMACHY's sun follower device controls the azimuth viewing direction during the occultation measurements. The mean azimuth direction has an error of about 1.5 mdeg, which is about 84 m in horizontal direction at the tangent point. We observe also a seasonal cycle of the azimuth mispointing with an amplitude of 2.4 mdeg, which is slightly increasing with time. The almost constant mean offset is 88 mdeg, which is about 5.0 km horizontal offset at the tangent point.
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Zhan, Yinhu, Shaojie Chen, and Donghan He. "High-Precision Heading Determination Based on the Sun for Mars Rover." Advances in Astronomy 2018 (August 1, 2018): 1–14. http://dx.doi.org/10.1155/2018/1493954.
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Since the American Mars Exploration Rover Opportunity landed on Mars in 2004, it has travelled more than 40 km, and heading-determination technology based on its sun sensor has played an important role in safe driving of the rover. A high-precision heading-determination method will always play a significant role in the rover’s autonomous navigation system, and the precision of the measured heading strongly affects the navigation results. In order to improve the heading precision to the 1-arcminute level, this paper puts forward a novel calibration algorithm for solving the comparable distortion of large-field sun sensor by introducing an antisymmetric matrix. The sun sensor and inclinometer alignment model are then described in detail to maintain a high-precision horizon datum, and a strict sun image centroid-extraction algorithm combining subpixel edge detection with circle or ellipse fitting is presented. A prototype comprising a sun sensor, electronic inclinometer, and chip-scale atomic clock is developed for testing the algorithms, models, and methods presented in this paper. Three field tests were conducted in different months during 2017. The results show that the precision of the heading determination reaches 0.28–0.97′ (1σ) and the centroid error of the sun image and the sun elevation are major factors that affect the heading precision.
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Tarng, Wernhuar, Kuo-Liang Ou, Yun-Chen Lu, Yi-Syuan Shih, and Hsin-Hun Liou. "A Sun Path Observation System Based on Augment Reality and Mobile Learning." Mobile Information Systems 2018 (2018): 1–10. http://dx.doi.org/10.1155/2018/5950732.
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This study uses the augmented reality technology and sensor functions of GPS, electronic compass, and three-axis accelerometer on mobile devices to develop a Sun path observation system for applications in astronomy education. The orientation and elevation of the Sun can be calculated by the system according to the user’s location and local time to simulate the Sun path. When holding the mobile device toward the sky, the screen will show the virtual Sun at the same position as that of the real Sun. The user can record the Sun path and the data of observation date, time, longitude, and latitude using the celestial hemisphere and the pole shadow on the system. By setting different observation times and locations, it can be seen that the Sun path changes with seasons and latitudes. The system provides contextual awareness of the Sun path concepts, and it can convert the observation data into organized and meaningful astronomical knowledge to enable combination of situated learning with spatial cognition. The system can solve the problem of being not able to record the Sun path due to a bad weather or topographical restrictions, and therefore it is helpful for elementary students when conducting observations. A teaching experiment has been conducted to analyze the learning achievement of students after using the system, and the results show that it is more effective than traditional teaching aids. The questionnaire results also reveal that the system is easy to operate and useful in recording the Sun path data. Therefore, it is an effective tool for astronomy education in elementary schools.
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Wullenweber, Nellie, Anna Lange, Alexei Rozanov, and Christian von Savigny. "On the phenomenon of the blue sun." Climate of the Past 17, no. 2 (April 30, 2021): 969–83. http://dx.doi.org/10.5194/cp-17-969-2021.
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Abstract. This study examines the cause of the blue colour of the sun as observed after the eruption of Krakatao in 1883 as well as other volcanic eruptions or massive forest fire events. Aerosol particles, e.g. volcanic ash or products of biomass burning, are believed to be able to modify the spectral distribution of transmitted solar radiation making it appear blue or green to a human observer. Previous studies already showed that narrow aerosol particle size distributions with radii on the order of about 500 nm can lead to anomalous scattering; i.e. scattering cross sections increasing with increasing wavelength in the visible spectral range. In this work we treat the effect of Rayleigh scattering on the shape of the transmitted solar spectrum correctly employing radiative transfer (RT) simulations with the SCIATRAN RT-model. The colour associated with solar transmission spectra is determined based on the CIE (International Commission on Illumination) colour matching functions and CIE chromaticity values. It is shown that a blue sun can be simulated for aerosol optical depths (at 550 nm) of about τ=0.5 (or higher) if Rayleigh scattering is taken into account. Without considering Rayleigh scattering – as in most of the previous studies – a blue sun is in principle produced with aerosol optical depths as low as about τ=0.1 (at 550 nm) if the aerosol particle size distribution is chosen to maximize anomalous scattering in the visible spectral range. It is demonstrated that Rayleigh scattering – as expected – has a strong impact on the transmission spectrum, particularly at low solar-elevation angles, and needs to be considered for a correct determination of the perceived colour of the sun. We also test the hypothesis that the blue sun after the eruption of Krakatao was caused by large abundances of water vapour in the atmosphere, as proposed in earlier studies. In addition, we present a case study on a particularly noteworthy blue sun event in the past, i.e. the one related to the large Canadian forest fires in September 1950.
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Moreno-Cruz, Isaías, Juan Carlos Castro, Omar Álvarez-Brito, Hilda B. Mota-Nava, Guillermo Ramírez-Zúñiga, José J. Quiñones-Aguilar, and Camilo A. Arancibia-Bulnes. "Development of an Elevation–Fresnel Linked Mini-Heliostat Array." Energies 13, no. 15 (August 4, 2020): 4012. http://dx.doi.org/10.3390/en13154012.
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Heliostats are critical components of solar tower technology and different strategies have been proposed to reduce their costs; among them diminishing their size to reduce wind loads or linking nearby heliostats mechanically, to reduce the overall number of actuators. This document aims to describe the development of a linked array of mini-heliostats which move together in an elevation–Fresnel configuration. This configuration consists of an array of mirrors rotating around linked parallel axes, in a linear Fresnel style with an added elevation mechanism allowing all axes to incline simultaneously in the plane North–South–Zenith; that is equivalent to an array of N linked mini-heliostats moved by only two drives instead of 2N. A detailed analytical study of the Sun-tracking performance of this kind of heliostat arrays was carried out, and an 8-mirror prototype based on optical and mechanical analyses was designed, built and tested. Even though the mirrors are flat, the array produced a rather compact radiative flux distribution on the receiver. The flux distribution is compatible with a slope error of the order of 1 mrad. Peak and mean concentration ratios reached 6.89 and 3.94, respectively.
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O'Sullivan, Lara. "Le Roi Soleil: Demetrius Poliorcetes and the Dawn of the Sun-King." Antichthon 42 (2008): 78–99. http://dx.doi.org/10.1017/s0066477400001854.
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Louis XIV may have made the image of the ‘sun-king’ his own, but the equation of monarch and sun has a long pedigree that stretches back into antiquity. For the Roman emperors, an association with Sol became commonplace, and both Caligula and Nero were explicitly saluted as νέος Ἥλιος. One of the earliest rulers to have adopted sun-related iconography within the western tradition is Demetrius Poliorcetes. His self-identification with Helius is not, to be sure, the most pronounced of his divine relationships. This was a king whose elevation to divine status in the Greek world of the late fourth and early third centuries was accompanied by a great number of religious and semi-religious associations: honoured by Athens as a Saviour, Demetrius himself seems to have cultivated above all an identification with Dionysus, whose combination of ferocity with a delight in wine and revels seems to have appealed to the character of the young king. Nonetheless, it is clear that imagery of the sun and of the heavenly bodies was employed of Demetrius in the representations of his status and power. The most explicit instance belongs to an ithyphallic hymn performed in Athens in 291/90 BC, in which Poliorcetes was hailed as the sun.
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Helbig, Nora, Henning Löwe, and Michael Lehning. "Radiosity Approach for the Shortwave Surface Radiation Balance in Complex Terrain." Journal of the Atmospheric Sciences 66, no. 9 (September 1, 2009): 2900–2912. http://dx.doi.org/10.1175/2009jas2940.1.
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Abstract The influence of topography on the radiation balance in complex terrain has so far been investigated either with very simple or very sophisticated approaches that are limited, respectively, by an uncontrolled spatial representation of radiative fluxes or heavy computational efforts. To bridge this gap in complexity, this paper proposes the radiosity approach, well known in computer graphics, to study anisotropic reflections of radiation in complex terrain. To this end the radiosity equation is rederived in the context of three-dimensional radiative transfer. The discretized equation is solved by means of an adapted version of progressive refinement iteration. To systematically study terrain effects, the geometrical disorder provided by the topography is considered in its simplest approximation by Gaussian random fields. These model topographies capture the most important length scales of complex terrain, namely a typical elevation and a typical valley width via the variance and the correlation length of the field, respectively. The mean reflected radiation is computed as a function of these length scales and sun elevation, thereby explicitly addressing finite system sizes and grid resolutions. A comparison with an isotropic parameterization of terrain reflections reveals that mean values are similar whereas spatial distributions vary remarkably. It is also shown that the mean reflected radiation in real topography is reasonably well characterized by the Gaussian approximation. As a final application of the method, the effective albedo of a topography is shown to vary with sun elevation and domain-averaged albedo, leading to albedo differences up to 0.025.
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Kuhn, Michael, Jakob Abermann, Michael Bacher, and Marc Olefs. "The transfer of mass-balance profiles to unmeasured glaciers." Annals of Glaciology 50, no. 50 (2009): 185–90. http://dx.doi.org/10.3189/172756409787769618.
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AbstractFor estimation of the mass balance of an unmeasured glacier, its area distribution with altitude, s (h), generally is the only available quantitative information. The appropriate specific balance profile, b (h), needs to be transferred from a measured glacier, where transfer means modification and adaptation to the topographic and climatic situation of the unmeasured glacier, such as altitude, exposure to sun and wind, or temperature. This study proposes the area median elevation, M, as a parameter of prime importance for the transfer. Using as an example ten Alpine glaciers, the similarity of M and equilibrium-line altitude is quantified and the effect of aspect and surrounding topography is qualitatively suggested. The transfer of b (h) between well-measured glaciers yielded differences in the mean specific balance of 150 mm in the mean of a 10 year period, which corresponds to a change in median altitude by 30 m. Transfer of b (h) with a shift according to median glacier elevation to a basin with 27 glaciers and 23 km2 ice cover agreed to within 10% with elevation changes converted from digital elevation models of 1969 and 1997.
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Liu, Li-Qun, Chun-Xia Liu, Jing-Si Wang, Kai Yang, Wen-Yu Zhang, and Hui-Min Gao. "Optimal azimuth and elevation angles prediction control method and structure for the dual-axis sun tracking system." Journal of Vibration and Control 21, no. 2 (July 4, 2013): 402–7. http://dx.doi.org/10.1177/1077546313484050.
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Schofield, Elizabeth, Jennifer L. Hay, and Yuelin Li. "Observation Effect in Ecological Momentary Assessments: A Study of Sun Protection Practices." Journal of Methods and Measurement in the Social Sciences 10, no. 2 (June 3, 2020): 95–110. http://dx.doi.org/10.2458/v10i2.23786.
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Daily diaries and ecological momentary assessments are plagued by the assessment itself becoming an intervention, known as the observation effect. Bayesian hierarchical level modeling is a technique to analyze repeated measures or multiple outcomes. In a study of twice-daily self-reporting of sun protection behavior among high-risk individuals, we investigate observation effects, agreement between retrospectively self-reported reminder effect and observation effect, differential observation effects, and consistency of behaviors. Participants who retrospectively reported no reminder effect showed a decrease in protective behaviors over time, whereas those who reported they were reminded showed sustained use. Advantages of the Bayesian methodology are demonstrated for assessing consistency of behaviors. Although we cannot observe prior behavior, we theorize that individuals experience an initial elevation at the onset of observation, though this unobserved increase is only sustained for a subset who later attribute this sustained behavior to a reminder effect. Implications for study designs with repeated observations are discussed.
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Mohd Rashid, Muhammad Ikram, Nik Fadhil bin Nik Mohammed, Suliana binti Ab Ghani, and Noor Asiah Mohamad. "Design, Development and Performance Test of Two-Axis Solar Tracker System." Applied Mechanics and Materials 704 (December 2014): 350–54. http://dx.doi.org/10.4028/www.scientific.net/amm.704.350.
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The energy extracted from photovoltaic (PV) or solar thermal depends on solar insolation. For the extraction of maximum energy from the sun, the plane of the solar collector should always be normal to the incident radiation. Sun trackers move the solar collector to follow the sun trajectories and keep the orientation of the solar collector at an optimal tilt angle. Energy efficiency of solar PV or solar thermal can be substantially improved using solar tracking system. In this paper, an automatic solar tracking system has been designed and developed using DC motor on a mechanical structure with gear arrangement. The movements of two-axis solar trackers for the elevation and azimuth angles are programmed according to the mathematical calculation by using the Borland C++ Builder. Performance of the proposed system over the important parameter like solar radiation received on the collector, maximum hourly electrical power has been evaluated and compared with those for fixed tilt angle solar collector.
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Zheng, Bangyou, Lijuan Shi, Yuntao Ma, Qiyun Deng, Baoguo Li, and Yan Guo. "Comparison of architecture among different cultivars of hybrid rice using a spatial light model based on 3-D digitising." Functional Plant Biology 35, no. 10 (2008): 900. http://dx.doi.org/10.1071/fp08060.
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Modification of plant types (i.e. plant architecture) is an important strategy to enhance the yield potential of crops. The aims of this study were to specify rice plant types using 3-D modelling methodology. The architecture of three typical hybrid rice cultivars were measured in situ in a paddy field using a 3-D digitiser at four development stages from the panicle initiation to the filling stage. The structural parameters of the rice canopies were calculated and their light capture and potential carbon gain were simulated based on a 3-D light model. The results confirmed that a plant type with steeper leaf angles let light penetrate more deeply with relatively uniform light distribution in the canopy at higher sun elevation angles, although this result was related to leaf area index. The variations of plant types, however, did not convert into differences of light distribution across rice varieties at lower sun elevation angles. Light use efficiency at the higher leaf area index could be enhanced by reducing mutual-shading. These results indicate that a promising approach to quantify the rice architecture in situ is to combine 3-D digitising and a 3-D light model to evaluate light interception and photosynthesis of rice plant types.
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El Kadmiri, Zakaria, Omar El Kadmiri, Lhoussaine Masmoudi, and Mohammed Najib Bargach. "A Novel Solar Tracker Based on Omnidirectional Computer Vision." Journal of Solar Energy 2015 (January 31, 2015): 1–6. http://dx.doi.org/10.1155/2015/149852.
Full textAbstract:
This paper presents a novel solar tracker system based on omnidirectional vision technology. The analysis of acquired images with a catadioptric camera allows extracting accurate information about the sun position toward both elevation and azimuth. The main advantages of this system are its wide field of tracking of 360° horizontally and 200° vertically. The system has the ability to track the sun in real time independently of the spatiotemporal coordinates of the site. The extracted information is used to control the two DC motors of the dual-axis mechanism to achieve the optimal orientation of the photovoltaic panels with the aim of increasing the power generation. Several experimental studies have been conducted and the obtained results confirm the power generation efficiency of the proposed solar tracker.