NOAA Weather Satellites
Antenna used for NOAA weather satellite reception. This is usually the 137 MHz turnstile antenna as shown above.
The US National Oceanic and Atmospheric Administration (NOAA) operate a number of earth observation satellites. Of interest to us are the NOAA series of low-earth-orbit satellites , which fly in sun-synchronous polar orbits, and which continuously transmit real-time earth imagery within the 137MHz space-downlink band.
Currently there are three NOAA satellites which may be received with modest VHF receiving equipment, namely NOAA 15, 17, 18 and 19. These satellites orbit at an altitude of ≈800km above the Earth's surface, with the plane of their orbits approximately aligned with the plane of the Earth's day/night terminator. In low earth orbit, satellites have a ≈100 minute orbital period, and for a mid-to-low latitude observer, each NOAA satellite will make 2-3 passes, each morning and evening.
The simple analog mode of NOAA image transmission is known as Automatic Picture Transmission (APT), which is broadcast in the 137MHz band. A higher resolution digital mode known as High Resolution Picture Transmission (HRPT), is transmitted at frequencies ≈1.7GHz. The current status of the APT and HRPT transmitters aboard the NOAA satellites is broadcast daily.
During 2004, NOAA/NASA issued an excellent 'booklet' describing the NOAA-N spacecraft. This comprehensive, well illustrated and eye-catching document, describes in plain language the various instruments aboard the NOAA-N spacecraft, as well as the history of NOAA polar orbiters, the launch, and operational details. If you are seeking comprehensive but readable description of how NOAA polar orbiting satellites work, this is the document for you. This booklet may be downloaded as a 40-page 1.4MB pdf file.