A weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. These meteorological satellites, however, see more than clouds and cloud systems. City lights, fires, effects of pollution, auroras, sand and dust storms, snow cover, ice mapping, boundaries of ocean currents, energy flows, etc., are other types of environmental information collected using weather satellites.

Weather satellite images helped in monitoring the volcanic ash cloud from Mount St. Helens and activity from other volcanoes such as Mount Etna. Smoke from fires in the western United States such as Colorado and Utah have also been monitored.

History

The first weather satellite, Vanguard 2, was launched on 17 February 1959. It was designed to measure cloud cover and resistance, but a poor axis of rotation kept it from collecting a notable amount of useful data.

The first weather satellite to be considered a success was TIROS-1, launched by NASA on 1 April 1960. TIROS operated for 78 days and proved to be much more successful than Vanguard 2. TIROS paved the way for the Nimbus program, whose technology and findings are the heritage of most of the Earth-observing satellites NASA and NOAA have launched since then.

Low Polar Orbit

Polar orbiting weather satellites circle the Earth at a typical altitude of 850 km (530 miles) in a north to south (or vice versa) path, passing over the poles in their continuous flight. Polar satellites are in sun-synchronous orbits, which means they are able to observe any place on Earth and will view every location twice each day with the same general lighting conditions due to the near-constant local solar time. Polar orbiting weather satellites offer a much better resolution than their geostationary counterparts due their closeness to the Earth.

The United States has the NOAA series of polar orbiting meteorological satellites, presently NOAA 17 and NOAA 18 as primary spacecraft, NOAA 15 and NOAA 16 as secondary spacecraft, NOAA 14 in standby, and NOAA 12. Europe has the Metop-A satellite. Russia has the Meteor and RESURS series of satellites. China and India have polar orbiting satellites as well.

APT/HRPT Communications

The Automatic Picture Transmission (APT) system is an analog image transmission system developed for use on weather satellites. It was introduced in the 1960s and over four decades has provided image data to relatively low-cost user stations at locations in most countries of the world. A user station anywhere in the world can receive local data at least twice a day from each satellite as it passes nearly overhead.

An APT signal is continuously broadcast, with reception beginning at the start of the next line when the receiver is within radio range. Images can be received in real-time by relatively unsophisticated, inexpensive receivers while the satellite is within radio range, which is typically 8 to 15 minutes.

NAME      FREQ.      APT/LRPT              NOTE

TIROS-N   137.500    OFF                   Tumbling out of control/Open carrier
NOAA 06   137.500    OFF                   Tumbling out of control/Open carrier
NOAA 09   137.500    OFF                   Tumbling out of control/Open carrier
NOAA 11   137.500    OFF                   Decomissioned 16 June 2004
NOAA 12   137.620    OFF                   Decomissioned 10 August 2007
NOAA 14   137.620    OFF                   Decomissioned 23 May 2007
NOAA 15   137.500    APT      ACTIVE
NOAA 15   1702.50    HRPT     ACTIVE
NOAA 16   137.620    OFF                   APT Inoperable
NOAA 16   1702.50    HRPT     ACTIVE 
NOAA 17   137.620    APT      ACTIVE
NOAA 17   1698.00    HRPT     ACTIVE
NOAA 18   137.100    APT      ACTIVE
NOAA 18   1707.00    HRPT     ACTIVE

FY-1D     1700.40    CHRPT    ACTIVE

Metop-A   137.100    HRPT                  A-side LRPT transmitter has failed
Metop-A   1701.30    AHRPT                 Transmitter failed

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