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Questions About Satellite Imagery

In its simplest form, satellite imagery is a picture of the Earth from space. These images are generated using sensors that perceive the reflectance of different wavelengths to create an image of clouds, water vapor, or land.

There are two main differences between these types of satellites; the orbit height and orbit direction.

Geostationary satellites orbit the Earth about 22,300 miles (35,800 km) above its equator, far enough out to allow the satellites a full view of the Earth or a "full-disk". They orbit the earth at speeds equal to the planet's rotation, which allows them to maintain their position over specific geographic regions, so they can provide continuous weather monitoring of that area over time. When weather systems form, the GOES satellites are able to monitor storm development and track their movements.

Polar satellites orbit the Earth roughly 14 times a day from pole to pole about 540 miles (870 km) above the ground. Data from the Joint Polar Satellite System (JPSS) 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, tropical cyclone monitoring, volcanic eruption monitoring, forest fire detection, global vegetation analysis, search and rescue, and many other applications.

The satellite footprint is the area of the Earth visible to the satellite. The ability to accurately view portions of the Earth deteriorates as the edge of the footprint is reached. Geostationary satellite footprints are much larger than those of polar satellites due to their distance from Earth.

Other than our 21-day archive, we do not archive imagery on this OSPO website. Additionally, at this time none of the sector or floater imagery is kept online past about 24 hours. Additional resources for archived imagery are listed below.

Most imagery and imagery products can be found in NOAA$apos;s Comprehensive Large Array-data Stewardship System (CLASS). As NOAA moves towards a cloud-based processing system, imagery and imagery products can also be found in the NOAA Open Data Dissemination (NODD) Program site -

In theory, the loops can be made longer. Past experience has shown that longer loops tend to take longer to load and require more system resources on the part of our users. As a result, we have tried to maintain a useful balance, by creating both standard and enhanced loops. If longer loops are desired, the images have unique file names and can be downloaded and saved to make loops as long as desired with any software of your choice. Imagery is deleted on a daily basis, usually around 03Z (10 pm EST or 11 pm EDT). Some sectors are deleted more frequently, with floater imagery deleted when moved. In the future, we hope to provide a few days worth of data archived from our sectors to make it easier for users to generate longer loops on their own systems.

Free public satellite imagery is not very good for seeing small details from space. In most cases, the resolution is too coarse to determine an individual structure, a residential street or a small town. Geostationary satellite resolution is at best 1 km and polar satellite resolution is a little better at 250m. That means one pixel in the satellite image, at best, represents 250 square meters of Earth in a polar image or one square kilometer in the Geostationary image. Only large objects would be visible in more than one or two pixels, or very large towns and cities would be visible, but quite pixelated and blurry. While there have been advancements in the satellite industry regarding resolution, much of the very high resolution imagery belongs to private industry companies or to the military.

Floater imagery is unique to geostationary satellites and has no preset location. A floater is created to focus on a particular event or location, such as major storms or natural disasters. These loops are snippets of the full geostationary image, and they are created to track the event or to "float" over the event being tracked. For example, floaters are often used for tropical cyclones and they track the storm as it moves throughout its lifecycle. Floaters are also used to quickly set up a loop over any given location or natural disaster such as fires, heavy precipitation events, earthquakes (for relief efforts), severe thunderstorms and any other areas of interest. Tropical floaters are set up automatically and should appear shortly after the Tropical Analysts begin classifications. Tropical Floaters are turned off within 12 hours of the last classification.

The dashed yellow line indicates a low pressure trough. For more information on the weather symbols used as part of the "Fronts" overlay, the Weather Service has put together an informative web page to explain all of the weather symbols.