These Engineering Development Units (EDUs) were used to test the functioning of the High Resolution Infrared Radiation Sounder (HIRS/4) and Advanced Very High Resolution imaging Radiometer (AVHRR/3) instruments on Polar-orbiting Operational Environmental Satellites (POES) before and after they were sent into orbit.
means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.These Engineering Development Units were used to test the functioning of the High Resolution Infrared Radiation Sounder and Advanced Very High Resolution imaging Radiometer instruments on Polar-orbiting Operational Environmental Satellites before and after they were sent into orbit.
Test units for the High Resolution Infrared Radiation Sounder and Advanced Very High Resolution Radiometer on the Polar-orbiting Operational Environmental Satellite, NOAA-N Prime. Engineering Development Units are used to develop instruments for satellites. They are also used to test updates that need to be made to instruments that are currently orbiting the Earth. After a mission is decommissioned, they can be used for education. The NOAA-N Prime was the last of the Polar-orbiting Operational Environmental Satellites to be on orbit and was part of the TIROS series. The POES constellation consisted of a pair of satellites that provided global coverage of several atmospheric and surface parameters. Between the two satellites, every part of the Earth was regularly observed at least twice every 12 hours. The POES system was decommissioned in August of 2025, but NOAA continues the critical mission of collecting weather observations from Low Earth Orbit through its next-generation satellite system, the Joint Polar Satellite System , which became operational with the Suomi National Polar-orbiting Partnership satellite in May of 2014. Building on the legacy of POES and working in coordination with other NOAA and partner LEO satellites, JPSS features more advanced instruments, delivers data more quickly, and improves the accuracy of weather forecasts. The Engineering Development Unit for the High Resolution Infrared Radiation Sounder on the Polar-orbiting Operational Environmental Satellite , NOAA-N Prime.An HIRS/4 measures scene radiance in the infrared spectrum. This data, along with data from an Advanced Microwave Sounding Unit-A instrument, is used to measure the temperature of the atmosphere at different levels from Earth’s surface to about 40 km altitude. It can also be used to determine ocean surface temperatures, total atmospheric ozone levels, water, cloud height and coverage, and surface radiance, and it has a visible channel that detects clouds. This information helps meteorologists accurately forecast the weather conditions that people experience on the ground. This animated graphic shows the Brightness Temperature for August 9-19, 2025 taken from Channel 1 of the High Resolution Infrared Radiation Sounder instrument on Polar-orbiting Operational Environmental Satellites satellite NOAA-19, which provides information on Earth’s atmospheric conditions and cloud patterns.The Engineering Development Unit for the Advanced Very High Resolution Radiometer on the Polar-orbiting Operational Environmental Satellite , NOAA-N Prime.The AVHRR/3 is a 6 channel imaging radiometer that detects energy in the visible and IR portions of the electromagnetic spectrum. It measures reflected solar energy and radiated thermal energy from land, sea, clouds, and the intervening atmosphere. Channels 3A and 3B operate during the daytime and nighttime portions of the satellite’s orbit, respectively. As the parameters they monitor evolve rather slowly, this preserves bandwidth and power for the other applications. The radiometer takes measurements from space to the ground to deliver information on the Earth's surface, both land and sea. It can even “see” through clouds. This data helps to determine where thunderstorms and tropical cyclones are forming, and where other hazards and disasters are developing. This chart shows the functions of all six channels on the Advanced Very High Resolution Radiometer instrument used onboard Polar-orbiting Operational Environmental Satellites satellites.This animated graphic depicts information on the underlying surface, either the cloud tops or the ground or sea, for August 2-12, 2025 taken from Channel 4 of the Advanced Very High Resolution Radiometer instrument on Polar-orbiting Operational Environmental Satellites satellite NOAA-19.Engineering Development Units are used to develop instruments for satellites. They are also used to test updates that need to be made to instruments that are currently orbiting the Earth. After a mission is decommissioned, they can be used for education. Because these EDUs are exact replicas of the on-orbit instruments, engineers can be confident that when they verify changes, they will behave as intended for the instrument on the satellite. And if something unexpected happens to the on-orbit instrument, they can recreate the issues in a test environment that reflects the conditions in space. Finally, after a mission is decommissioned, as POES was in August of 2025, EDUs are the only flight hardware that remain on Earth. They represent the life cycle of a satellite’s instruments, serving first as “beta” models, then testing units, and finally as a physical legacy of the POES satellite series.An artist's rendition of a NOAA polar-orbiting satellite. These satellites circle the earth in a north-south orbit, passing close to both poles.Have an idea for an artifact, photo, or document from NOAA’s history that you think we should feature in “Friday Finds!”? Send an email with a description and, if possible, a photo to
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