Observational and analytical studies on influence of urban surface structure on radiation balance components

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Influence due to urban surface structure on the change of radiation balance components in the groundsurface is investigated. In paticular, this study aims at explaining additional longwave radiation from urban surface obstructions by their screen- effects, namelly their screen-factors and surface temperatures based on thermal image analysis. The main results are summarized as follows : (1) The fundamental concept of longwave radiation field at night is proposed in and around urban areas. (2) The horizontal distributions of screen-factor (namelly, wall view-factor) are estimated from a fish-eye lens image in various cities of Kanto region. It is shown that the screen-factor in built-up area is about 10 - 75%. (3)Thermal image analysis is tried on rock-surface temperature of sandstone used for a masonry bridge pier with simple structure, and sufficient results are obtained. Therefore, thermotracer measurement can be applied usefully to investigate the actual states of wall surface temper … More ature pattern in urban canyon. (4) The warming of wall surface temperature in winter is investigated in a maltiple dwelling house by thermal image analysis, and the influences of room heating and solar radiation on its warming are discussed. The results show that solar radiation heats more effectively wall than windowpane and roomheating heats more effectively windowpane than wall, and the increased radiation (4-26W/m2) by the both heating effects are attached great importance to additional longwave radiation from surface obstructions. (5) Every longwave radiation balancecomponent changes almost lineally with the screen-factor. It becomes clear that additional longwave radiation from urban surface obstructions is sufficiently estimated from their screen-effects, if their surface temperatures are estimated separately in three different materials based on thermal image analysis. (6) In the daytimes within urban canyon, additional longwave radiation increases more than at night, but net radiation decreases due to the shade-effective decrease of solar radiation. Street shade trees mitigate all radiation components. Less