]> >Heat flux averaged over a layer of air, such as the boundary layer; heat-flux divergence or difference between the top and bottom of a layer. Antenna temperature is a way of expressing the brightness of a radiation source - it is proportional to the power per unit area emitted by the source. In most cases where it is used it corresponds to the thermodynamic or physical temperature of the source being observed. It thus relates the power emitted by the source to an interesting physical property of that source. A descriptive measure of radiation in terms of the temperature of a hypothetical blackbody emitting an identical amount of radiation at the same wavelength. A process in which a system does not interact with its surroundings by virtue of a temperature difference between them. Adiabatic Process A temperature-measuring system in which the thermally sensitive element is located at a distance from the indicating element.