The Research of Urban Surface Albedo

 

What is Albedo?

Solar reflectance, so-called Albedo, is a ratio of reflected solar radiation, which includes with visible light, near-infrared light, and ultraviolet light, to the total amout that incidents on that surface. Albedo ranges from 0 (for perfect absorptance) to 1 (for perfect reflectance). For example, a cured gray-cement concrete has an Albedo appriximately ranging 0.35-0.40, asphalt 0.05-0.1, dark-colored glass 0.5, and so on. These examples are simple surface cases. While, if you talk about rough surfaces just like urban situations, you have to take the trapping effect of an urban canyon into account. This means that the urban Albedo is affected by not only the surface materials of buildings but also the urban geometry.

Background and Our Scope

Albedo is one of the important parameters used to estimate Urban Heat Island particularly when you involve with the so-called meso-scale model. In line with the study of radiation exchange within urban canopy, how much of urban Albedo you assume in the model is quite significant. Up to now, the urban canopy Albedo corresponding with the influence of urban geometrical structure has been examined by several observations such as remote-sensing approach or numerical calculations. Particulary, numerical approach seems to be effective, since the mechanism of radiation exchange in an urban canopy can be described on the stage of an obvious physical process. However, unfortunately, there are not good enough stocks to provide a plausible Albedo assumption for the meso-scale model because of a lack of knowledge coming from systematic and comprehensive explanation. Then, here, we establish a 3D numerical model to obtain an urban Albedo. And following the modeling, sample data base are aquired through a huge amount of numerical experiments to make clear factorial effects on Albedo such as building size, height and its variation, road width, surface reflectances of wall, roof and road. Finally, we offer these fruits we have attained as a form of smart computer tools. The smart tools offered by us have been separated into 2 portions: the Albedo Calculator version 0.1 and the Albedo Viewer Web-Application. The former deals with a user's demand who has a particular input-condition. Whereas, the latter responds very quickly if you have a possible input-condition that has been considered within the data base.

Principle of Albedo Calculation

In fact, the real urban structures are notsimply geometric and have no uniformity,so it is difficult to determine the certainvalue of thier Albedo. Here, we supposedan urban configulations as followings tofacilitate the simulation.

  • the entire buildings are uniform size andlocated homogineously along identical roads,

  • the set of building blocks has the same heightor only two different heights upon specifiedpatterns.

Introduction of Calculation Model

Radiation exchanges are taken into account within a range of only one unit area, since four surroundings boundaries are treated as cyclic-loop. Each facet of unit area (including roof, wall, and road) is specified rectangular grids (n grids) in order to precisely calculate solar radiation emitted into the urban canopy. The multiple reflections of reflected radiation are simulated by using vector tracking method. The numerous vectors are casted from the center of hemisphere positioned on the center of each grids. (see more detail)

 

Albedo Calculator version 0.1

Albedo Viewer Web-Application

Albedo Calculator provides you a wide range of condition settings and full numerical simulation. It might be useful for one who requires the results in deep. Help of the tool has details how to use this splendid program.

Albedo Viwer offers a user to access the prepared database enable getting Albedo results from our website via internet. The data can be provided with 2 parts as;

Download Albedo Calculator

*Click on the picture to download the ALBEDO Calculator version 0.1 or click here

Part #1 : Buildings having a same height

Click away to Web-Application of Part #1

Part #2 : Buildings having two different heights

Click away to Web-Application of Part #2

*Click on the picture to reach its corresponding application. Note that, you may take a few minutes waiting for loading database.

Note: The details of response tables of albedos related with the full factorial design experiments are provided here (PDF File).

 

visitors since Jun. 17, 2003