The National Oceanographic and Atmospheric Administration (NOAA) of the United States of America supports several Weather Satellites in Low Earth Orbit. Currently these are NOAA-15, NOAA-18 and NOAA-19.
All three satellites broadcast using a system known as Automatic Picture Transmission (APT). These satellites scan the Earth, 840 kilometres beneath them, continuously. This results in images that build up line by line, similar to how the image on a TV screen is generated, a complete APT image takes 12 to 14 minutes to build up at a rate of two lines per second. These transmissions are received on frequencies in the VHF 137MHz band. A typical NOAA satellite APT images consist of two frames, side by side as shown in the left-hand “PRISTINE” images below. The very left part of the images are acquired in visible wavelengths; that to the right is imaged in infrared. These images are transmitted as greyscale images (i. e. no colour). Software is used to decode the VHF transmissions and a colour palette is applied depending on the cloud temperatures