Low Earth Orbit Satellites

The National Oceanic and Atmospheric Administration (NOAA) operates two sets of satellites to monitor the weather: geostationary satellites (geostationary operational environmental satellites - GOES) and low Earth orbit satellites - POES. Weather data is also available from Defense Meteorological Satellite Program (DMSP) satellites in low Earth orbits.

The NOAA low Earth orbit weather satellites are operated in a special polar orbit, a sun synchronous orbit. In a sun synchronous orbit, the satellite passes over the same spot on Earth each day at the same time. The satellites are operated in pairs with one satellite making a morning pass and the other satellite making an afternoon pass. This pattern ensures that every spot on the Earth is observed by a NOAA weather satellite at least every six hours and typically every four hours.

Illustration of the path of a sun-synchronous polar orbit. Image from NASA Earth Observatory.

There are multiple instruments on the NOAA low Earth orbit satellites. Some of the data the POES satellites collect globally every day include: information on cloud cover, surface distribution of ice and snow, temperature and moisture in the atmosphere, sea surface temperature (SST), land surface temperature and distributions of aerosols and ozone. An important advantage of low Earth orbit satellites over GOES is that they can detect temperature and moisture structure below the cloud top due to the use of microwave instruments as they are much closer to the Earth.

Passive microwave imagery from the NOAA weather satellites and DMSP satellites shows features that cannot be seen with other sensors due to high cloud cover obscuring the view. Passive microwaves "see through" non-raining clouds and view rainbands, eyewalls and eyes even when obscured by upper-level clouds. The microwave data provides good information on precipitation and clouds at low and medium levels. It gives valuable clues concerning the intensity and position of storms. This data is used in weather forecasts and the forecasting and modeling of tropical cyclones.

Two images of typhoon Zeb intensifying in the western Pacific. In the microwave image on the left, dark blue marks a developing eye at the center of circulation. This dark blue coloration suggests abundant low-level cloud water in the eye but no deep convection above. The greens and yellows in the spiral bands represent scattering signatures from precipitation-size ice particles above the freezing level. The infrared image on the right shows the cirrus clouds and cumulonimbus that covers most of the storm. It shows a portion of the eye. However, the northern part of the eye is covered by cirrus clouds. Navy Research Lab Monterey, Marine Meteorology Division.

Examples of the imagery produced by the NOAA low Earth orbit satellites are seen below.

A mosaic of images from the visible image data gathered onboard NOAA's low Earth orbiting satellites from September 30, 2009. Land is outlined in purple. NOAA.

Composite image of total water available for precipitation in the atmosphere (Total Precipitable Water - TPW). Units are in mm of water. White streaks are areas without data from this set of satellite orbits. NOAA.

Visible imagery, Hurricane Isabel in the Atlantic Ocean, September 15, 2003. The image was taken as the sun rises, coloring the right side of the image. Land is outlined in white. South Carolina, where Isabel would make landfall on September 18, can been seen in the upper left corner. NOAA.