Brightness Temperature; What is 'brightness temperature'?
Brightness Temperature; What is 'brightness temperature'?
Brightness Temperature
is another way of measuring the amount of energy coming from an object.
All objects naturally emit energy in a process called "thermal
emission" or "black body emission." (Everything around you - planets,
your chair, and even you - emit this energy.) In the simplest case, the
amount of energy emitted depends only on the physical temperature of the
object. So, when we say something has a brightness temperature of 100
Kelvin, we mean it is giving off as much energy as something that is at a
temperature of 100 K. The brightness temperature, however, is not
always the true physical temperature of an object! Some materials emit
slightly more or less energy than other materials even when they are at
the same temperature, and sometimes things emit energy by other means in
addition to thermal emission. This can make their brightness
temperature much higher than their physical temperature. The emission
from Jupiter at S-band is an example of this.
Brightness temperature
is most often used when talking about planets. One reason for this is
that it sometimes gives us an idea of the true physical temperature of
the planet. Another reason is that, just as Normalized Flux, brightness temperature accounts for the changing distance of the planet.