Net radiation of urban areas

In urban climatology the climate of our urban environment is studied. In the cities the major part of mankind is living. In Central Europe up to 75 % of people are living in cities or urban agglomerations. Also in other parts of the world this is an increasing problem which has to be considered more and more. One example is Japan or the Korean Republic, which are densely populated countries with an urban population of 78 % resp. 81 %. Urban climate differs completely from rural conditions. Since urban surfaces are extremely heterogeneous the interaction with the urban boundary layer is very complex and there are only a few micro-meteorological measurements existing providing us with sufficient data of the urban radiation and energy balance. On the other hand spatially distributed data sets of various meteorological elements are required from the user community (e.g. planners) to improve numerical models. For many years remotely sensed data have been used in urban climate studies. Most of these data are in the thermal infrared band between 8 and 14 urn and the IR-images are widely used to outline the urban heat island. But long-wave emission, calculated from surface temperature data is only one variable among others which are important to characterise radiation and heat balance of a landscape. It is shown how satellite data can be used (1) to get insight of the urban radiation scheme and (2) to help to explain the discrepancies between surface temperature and air temperature on a physical basis.