Complementing the geostationary satellites are polar-orbiting satellites known as POES, S-NPP, and JPSS-1 (now NOAA-20). NOAA-20 is the first of the JPSS
Series. Polar orbiting satellites constantly circle the Earth in an almost north-south orbit, passing close to both poles.
The POES satellite system offers the advantage of daily global coverage, by making nearly polar orbits 14 times per day approximately 520 miles above the surface of the Earth. The Earth's rotation allows the satellite to see a different view with each orbit, and each satellite provides two complete views of weather around the world each day. NOAA partners with the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) to constantly operate two polar-orbiting satellites – one POES and one European polar-orbiting satellite called Metop.
The POES instruments include the Advanced Very High Resolution Radiometer (AVHRR) instrument and the Advanced TIROS Operational Vertical Sounder (ATOVS) suite. The EUMETSAT-provided Microwave Humidity Sounder (MHS) instrument completes the ATOVS suite. The AVHRR/ATOVS provides visible, infrared, and microwave data which is used for a variety of applications such as cloud and precipitation monitoring, determination of surface properties, and humidity profiles.
Data from the POES series supports a broad range of environmental monitoring applications including weather analysis and forecasting, climate research and prediction, global sea surface temperature measurements, atmospheric soundings of temperature and humidity, ocean dynamics research, volcanic eruption monitoring, forest fire detection, global vegetation analysis, search and rescue, and many other applications.
The orbits are circular, with an altitude between 830 (morning orbit) and 870 (afternoon orbit) km, and are sun synchronous. One satellite crosses the equator at 7:30 a.m. local time, the other at 1:40 p.m. local time. The circular orbit permits uniform data acquisition by the satellite and efficient control of the satellite by the NOAA Command and Data Acquisition (CDA) stations located near Fairbanks, Alaska and Wallops Island, Virginia. Operating as pair, these satellites ensure that data for any region of the Earth are no more than six hours old.
A suite of instruments is able to measure many parameters of the Earth's atmosphere, its surface, cloud cover, incoming solar protons, positive ions, electron-flux density, and the energy spectrum at the satellite altitude. As a part of the mission, the satellites can receive, process and retransmit data from Search and Rescue beacon transmitters, and automatic data collection platforms on land, ocean buoys, or aboard free-floating balloons.
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