Environmental Engineering Reference
In-Depth Information
instrument screen. Second, there are differences between satellite systems in terms of
their spectral responses and instrumental calibration. Third, there are problems in making
generalizations about Earth as a whole when assumptions have to be made about areas
that are less well monitored or when temporal sampling is not systematic. For example,
the polar orbiting satellites will cover different parts of Earth's surface at different times
of the day, depending upon their orbit. This can be significant in diurnal variability of
cloud. Hence not all the figures in this chapter are based on the 1990s, as such studies are
time-consuming and difficult. Nevertheless we now know much more about the
magnitude of inputs and outputs of energy within the earth-atmosphere system.
Figure 3.5
Global distribution of mean annual net radiation.
Units are W m
-2
. Source: After Budyko et al. (1962).
of solar radiation. The difference between incoming and outgoing radiation is known as
net radiation or the radiation balance. For Earth's surface, values are shown in Figure 3.5.
If we include the effects of the atmosphere the picture changes. The atmosphere has a
negative balance, even in
