Applications of aerophotos & satellite images in correlation analysis between urban thermal field and architectural volume rate
-----------taking Shanghai as an example--------
Wang zhisheng, Qian Bin, Guo Shulin
Department of Geography, shanghai Teachers,
university, 10 Gulin Road, Changhai 200234, China
Abstract
In this paper, by taking advantage of the interpretation data of color aerophotos with large scale and the thermal field data from the thermal IR images of meteorological Satellite and Landsat TM, an optimization correlation model between earth surface structure and thermal field in shanghai proper has been established, in which, the effect of heat carrying and energy storage of urban "canyon" is simulated by adopting the digitized factor of "urban architectural volume rate" (UAVR) which is the first to be designed. It has been proved by its calculated results that UAVR is the dominant factor fro causing thermal field temperature difference between the city & country, and within the city., the concrete contributions of other factors, such as waters and vegetation etc to thermal field are further described, as well as the characteristics of their variations with the seasonal change. It has been pointed out that the method for simulating the energy storage and heat carrying of urban underlying surface by using the digitized factor of UAVR has more significant feasibility and advantages that that for studying the "canyon" effect constituted between the building in the city by adopting the wind tunnel simulation and instrument measurement.
Foreword
The urban thermal field has been studied for 173 years, yet, the difference between urban and rural air temperature field the phenomenon of heat island has been more discussed, the mechanism of this phenomenon has been worked by many experts at home and abroad, and concluded by some experts. City, being the product of human activities, has been classified as the source of generating artificial heat during the climatologists discussing the thermal equilibrium of the mechanism of heat island. This is because of the thermal characteristics of surface structural radiation field which is closely related to the urban architectural scale different functional regions changed by mankind. In this paper using satellite thermal IR images and the interpretation data of 1/5000 color aerophotos an optimization model between Shanghai earth surface structure and its thermal field has been emphatically discussed, and the contributions of "urban architectural volume rate" (UAVR) to forming urban thermal field admits importance for forming "heat island" have been established.
Theoretical basis and information source
It is known from the radiation theory that energy can be emitted outward in the form of electromagnetic wave by the body with surface temperature greater than 0 k, and it can be expressed as :
Q = e
sT4
Where Q is the radiation energy flux (w/m
2),
s the Stefan-Boltzmand constant (5.669 x 10
-8 w/m
2k
4)
e the emissivity and T the surface temperature of the body (k).
Based on this equation the radiation flux is not only related to the earth surface temperature, but also dependent on the emissivity and T the surface temperature of the body. Nevertheless, it is not very easy for one city to obtain a correct distribution of value Q (here, refer mainly to logn wave radiation Q emitted from earth surface. Fuggle & Oke pointed out in 970 that for this factor the different. Albedo and thermal capacity of urban surface structures should also be considered, that is why oke did the experiment on the effect of "metropolis canyon"
[2].
Based on the theory mentioned above, the factor "urban architectural volume rate and other factors of urban underlying surface have been designed in this paper of participating the regression analysis of urban thermal radiation field, while the definition of the fuctor is
UAVR = ( Building covering area x building storey / Unit area ) x 100%
1 km is taken as unit are, while 320km, are taken in total in Shanghai proper. This factor is used for representing the average "canyon" effect model formed between every square kilometer of macroscopic field of 320km in shanghai proper.
Information source: A. Interpretation database of 1/5000 Shanghai color aerophotos taken in May, 1988. B. Shanghai thermal field database from thermal IR images for materological satellite, three images in total, the time is about 10:00 May 18, 1987.
