Everybody knows that there is no any emitting, absorbing and scattering medium between the Sun and the upper atmosphere of the Earth. But the propagation of solar radiation in the atmosphere cannot be considered without taking into account both absorption and scattering of the incident radiation by atmospheric gases, aerosol particles and clouds of water droplets and ice crystals. One can see that even this well-known natural phenomenon is not simple because there is a participating medium between the radiation source and the earth surface. Obviously, similar or even more complex problems should be solved in astrophysical studies of the radiation transfer in space dust clouds and in the atmospheres of stars and planets
As for our home planet, we will find a lot of natural and engineering problems with important effects of radiation transfer in emitting, absorbing, and scattering media. Of course, the heat transfer by radiation in the atmosphere both in the visible and infrared spectral ranges is a good and practically important example. At the same time, we should remember some other important processes which take place in diverse combustion systems, in high-temperature material processing and even in the present-day electronic equipment. One cannot predict the behavior of forest fires, the pollution of the environment by industrial furnaces, and the performance of advanced highly-porous thermal insulations without a detailed analysis of the radiation transfer in a medium which absorbs, emits, and scatters the radiation.
The traditional radiation transfer theory based on a phenomenological approach to the energy transfer by radiation appeared to be applicable to numerous practical problems. The mathematical technique of this theory is well elaborated and widely used in atmospheric problems, thermal engineering and even in some medical applications. Therefore, the first topic which follows from the present introductory article is entitled “Radiation transfer theory and the computational methods”.
It is clear that even very good and complete set of the computational tools for radiative transfer calculations would be totally fruitless without knowledge of medium radiative properties. This is a separate branch of the radiation science because the radiative properties of pure substances and small particles cannot be obtained by a phenomenological approach without a detailed study of physics of specific processes responsible for emission, absorption, and scattering of electromagnetic waves by gases, plasma, macroscopic particles and bulk materials. For these reason, the following two important topics are involved in this branch of the Radiation Area: “Spectral radiative properties of gases and plasma: theoretical models and experimental data” and “Spectral radiative properties of disperse systems: theoretical modeling and experimental characterization”. It should be emphasized that there are articles on both theoretical models and experimental data in these topics. Moreover, the experimental methods for analysis of absorption and scattering characteristics of dispersed materials are also presented in the second topic. These methods are usually based on solutions for inverse problems to determine the material radiative properties from the spectral measurements of reflectance and transmittance of an incident radiation by the material samples.
The educational mission of the Thermopedia project cannot be accomplished without a set of representative examples illustrating some typical applications of the methods and physical data reported in a large body of single articles. It is a motivation of our efforts in elaborating the topic entitled “Radiation transfer problems in nature and engineering”. A reader can find there some contributed articles but the work is in progress now and we are going to arrange a permanent completing of this topic by contributions of leading researchers working in the field of radiation transfer. We hope that these articles will provide good examples for students, engineers, and researchers who are in the beginning or in the middle of the way to the high-level research and engineering skill.