- 标题
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Investigation of Sentinel-2 Bidirectional Reflectance Hot-Spot Sensing Conditions
摘要： Directional reflectance effects, often described by the bidirectional reflectance distribution function (BRDF), occur in Sentinel-2 multispectral instrument reflectance. The bidirectional hot-spot is a special case of the BRDF used to describe the increased backscatter reflectance that occurs over most surfaces when the solar and viewing directions coincide. A global year of Sentinel-2A metadata extracted using the Committee on Earth Observation Satellite Visualization Environment (COVE) tool and an established astronomical model were used to quantify the range of solar geometry and scattering angles expected in Sentinel-2A data. The established astronomical model was adapted to be Sentinel-2A specific and was parameterized as a function of the sensor acquisition date and nadir latitude. Solar zenith angles varied from 15.335° to 91.454°, and the scattering angles varied from 84.714° to 173.967°. To confirm the global COVE results, the scattering angles of a sample of Sentinel-2A data were examined and differed by less than 0.17° with respect to the COVE data. Given that hot-spots are only apparent when the scattering angle is close to 180°, we conclude that hot-spot will not occur in Sentinel-2A data. Equations and software to predict the scattering angle at the Sentinel-2A swath edge as a function of acquisition date and nadir latitude are provided so users may obtain data over a range of scattering angles in support of their BRDF studies.
关键词： bidirectional reflectance distribution function (BRDF),Bidirectional hot-spot,scattering angle,solar geometry,Sentinel-2
更新于2025-09-23 15:23:52
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Solar Engineering of Thermal Processes, Photovoltaics and Wind || Solar Radiation
摘要： The sun’s structure and characteristics determine the nature of the energy it radiates into space. The first major topic in this chapter concerns the characteristics of this energy outside the earth’s atmosphere, its intensity, and its spectral distribution. We will be concerned primarily with radiation in a wavelength range of 0.25 to 3.0 μm, the portion of the electromagnetic radiation that includes most of the energy radiated by the sun. The second major topic in this chapter is solar geometry, that is, the position of the sun in the sky, the direction in which beam radiation is incident on surfaces of various orientations, and shading. The third topic is extraterrestrial radiation on a horizontal surface, which represents the theoretical upper limit of solar radiation available at the earth’s surface. An understanding of the nature of extraterrestrial radiation, the effects of orientation of a receiving surface, and the theoretically possible radiation at the earth’s surface is important in understanding and using solar radiation data, the subject of Chapter 2.
关键词： solar radiation,extraterrestrial radiation,diffuse radiation,solar geometry,spectral distribution,solar constant,beam radiation
更新于2025-09-16 10:30:52
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Photovoltaic performance of one axis multiple-position sun-tracked PV panels
摘要： In this article, the photovoltaic performance of one-axis multiple-positions sun-tracked photovoltaic panels (MP-PV) is investigated based on solar geometry and dependence of photovoltaic conversion efficiency on the incident angle (IA) of solar rays on PV panels. For such PV system, the azimuth angle (AZA) of PV panels is daily adjusted several times (M) from eastward in the morning to westward in the afternoon by rotating PV panels about inclined north-south axis (INSA) to ensure the projected incident angle (PIA) of solar rays on the plane perpendicular to INSA is always less than the specified angle θa. Results show that, the annual electricity generation (AEG) of MP-PV increases with the increase of M, but such increase is not noticeable when M>5. For MP-PV with the tilt-angle (β) of INSA being yearly fixed (1T-MP-PV), the optimal θa of 3P-,5P- and 7P-PV for maximizing AEG are respectively 24o, 15o and 11.5o, and their AEGs are respectively about 92%, 94% and 95% of that from similar 2-axis tracked PV panels (2A-PV). Whereas for MP-PV with the β being yearly adjusted four times at three tilts (3T-MP-PV), the optimal θa of 3P-, 5P- and 7P-PV are respectively about 22.5o, 14.5o and 11o, and the Pa are respectively about 96%, 98% and 99% of that of similar 2A-PV systems.
关键词： photovoltaic conversion efficiency,azimuth angle,annual electricity generation,solar geometry,sun-tracked PV panels,incident angle,photovoltaic performance
更新于2025-09-16 10:30:52