As noted in the Satellites chapter, GOES and polar orbiting satellites return both visible
and infrared (IR) images. Visible images are created by sunlight reflected from cloud
tops. Smooth cloud tops will give a much different reflected signal than clouds that are
irregularly shaped. However, two layers of smooth, thick clouds will reflect sunlight in a
similar manner making relative height determination difficult. In some cases, if the lay-
ers overlap and the sun angle is aligned properly, shadows will reveal the height differ-
ences. In most cases, the best way to determine cloud top height is by the use of
infrared imagery. Infrared sensors detect the radiation emitted by clouds. Because tem-
perature decreases with height in the troposphere, higher clouds will appear colder (or
whiter) on the satellite images. If image enhancement software is available, the differ-
ences can be accentuated.
Some types of clouds are not observed well by satellites. Small clouds, such as fair
weather cumulus, are simply too small to be resolved by the satellite sensors. Clouds
which are thin or scattered also may not be observed well (figure 34). For a thin or
scattered cloud, a GOES infrared detector will receive infrared radiation from both the
colder cloud fragments, and in the clear spaces—from the warmer Earth. When the
total radiation is averaged, the satellite will clouds that appear warmer due to this
heterogeneous field of view.
figure 34.
Prior to looking at images it is important to be familiar with the clouds. Clouds most
often associated with mid-latitude cyclones are listed below and discussed in the
following paragraphs.
Upper Level Clouds (6–12 km): Cirrus (Ci), Cirrostratus (Cs), Cirrocumulus (Cc),
Cumulonimbus (Cb)
Mid Level Clouds (2–6 km): Altostratus (As), Altocumlus (Ac)
Low Level clouds: Stratus (St), Stratocumulus (Sc), Cumulus (Cu)
satellite field of view