Channel 4 Cloud Top Interpretation

  1. The higher the altitude, the colder it gets (usually).
  2. An Infra-Red picture is a measurement of temperature only, not light (for channel 4 at 10.7 um).
  3. Infra-Red pictures show the temperature of objects.
  4. The grey scale on the IR picture gives an indication of heat measured.
  5. The lighter the gray shade, the colder the object.
  6. Objects radiate energy, including clouds, water and the ground.
  7. The higher clouds mask the radiation of lower clouds, water and ground, unless very thin.
  8. Some grey scale ranges on this site's Channel 4 imagery are converted into colour bands.
  9. These colour bands make it easier to identify the temperature (hence approximate height) of cloud tops.
  10. The rate at which the temperature drops with height is called the Lapse Rate.
  11. The standard ISA lapse rate is 1.98 per 1,000 feet.
  12. The lapse rate actually varies according to various factors.
  13. When making a temperature/height correlation, although the temperatures are quite precise, treat the height figure with a grain of salt.
  14. Thunderstorm cells and cell clusters have often very high cloud tops (hence are colder) and usually poke through other clouds.
  15. High clouds don't necessarily mean thunderstorms; but this is a possibility especially if the highest cloud tops are very localized and/or sharply defined.
  16. Before flying, ask your dispatcher or flight service station weather briefer to confirm your observations using other sources (doppler radar mainly).