Information About the Satellites and the Images

...a part of the International Weather Satellite Images.

General Geostationary Satellite Information and Images

Geostationary satellites are called geostationary because they are in orbits so that they go around the Earth at the same rate at which the Earth rotates on its axis, so that they stay in the same position relative to the earth. Because of this, certain areas of the world are better covered by the geostationary satellites than others, and polar areas are always covered poorly. They orbit the earth at an altitude of about 35,785 km (22,235 mi.) above the equator (almost three times the diameter of the earth), and therefore can "see" almost (not quite) half of the sphere of the Earth from their position.

The geostationary satellites take images over a period of a few minutes (up to 26 minutes for a GOES-8 full earth scan) to scan the earth line by line. The older satellites (GOES-7 and older, GMS to present, METEOSAT to present) did so as they spin at 100 times per minute. The newer satellites (GOES-NEXT series, which is GOES-8 onward), as well as some older satellites (INSAT, GOMS) are three-axis stabilized (stabilized on all three 3-D axes relative to the Earth) satellites, which do not spin.

Sources for information above and Other Information:

The following are the major geostationary satellites:

Satellite programCurrent SatelliteLongitudeCountryOperational AgencyLaunch AgencyViewComment
METEOSATMETEOSAT-7InternationalEUMETSATESAEastern Atlantic, Europe, AfricaHigh resolution images encoded
INDOEXMETEOSAT-563°EInternationalEUMETSATESAAsia, Indian Ocean, AfricaHigh resolution images encoded
GOMSGOMS-1 (ELEKTRO)76°ERussiaAsia, Indian Ocean, Eastern AfricaImages intermittent
INSATINSAT-3(?)90°E (?)IndiaAsia, Indian OceanAll images encoded
Feng-YunFeng-Yun-2B105°EChinaAsia, Indian Ocean, AustraliaSatellite Failed
GMSGMS-5140°EJapanEast Asia, Western Pacific, Australia
GOES (WEST)GOES-10135°WU.S.A.NOAANASAEastern Pacific, North America
GOES (EAST)GOES-875°WU.S.A.NOAANASANorth and South America, Western Atlantic

General Polar Orbiting Satellite Information

The NOAA satellites are the American polar orbiting satellites. These satellites are much closer to the earth than the geostationaries and move over different points on the earth. Other countries have polar orbiters as well, but less data are available from those satellites.

The polar orbiters orbit the earth much lower than the geostationary satellites. Because of this, they do not capture as much area at once when they are recording images of the Earth. As they travel along their path, they take a swath image, meaning they take are imaging only the points on the perpendicular to their path of travel. There is considerable distortion at the "horizon" at the edge of this perpendicular plane. As they move over the earth, they continue to take these images, and they combine to form an image which is considerably longer than it is wide, and has distortion at the sides (compacting). The two ends of this image were taken at two different times (and all of the lines in the middle taken between the two times). As they travel, they transmit the data that they are collecting to receiving stations on the Earth at a certain freqency. Information on receiving these images is available at the Polar Orbital Weather Satellite Pictures Homepage.

Most polar orbiter sites are sites that are associated with receivers that receive the images that were taken over the area near the site. Two sites, though, have all the images that were taken by the satellites: the SAA and DMSP.

Types of Images

Visible images show the visible light that is reflected off of clouds and the surface of the earth. They show all types of clouds and are the best type of images for seeing low level systems, which do not show up well on infrared imagery. Visible imagery is only taken during the day (in the area where the satellite is located).
Infrared imagery shows the amount of heat emitted by the different cloud features and the surface of the earth. Infrared images show clouds at higher levels better because they are colder. The images shown are really negatives of the images, because areas that are white are ones that are colder (emit less infrared light), and areas that are dark are warmer. This is done so that the images look similar to visible images.
Enhanced Infrared
Enhanced infrared images are simply infrared infrared images with the coldest areas in colors so that the different temperatures can be distinguished from each other. This is often good for showing the height of clouds which is important for determining the strenth of systems in the tropics. Many infrared images are enhanced, and not all enhanced infrared images are labled as such in this page.
Water Vapor
Water Vapor images are images that show water vapor in the upper troposphere. This tropophere is the only area of the atmosphere generally important in everyday weather forecasting. The systems shown by water vapor images are upper level systems and are often different from those found at the surface. These systems have a large effect on the systems that are found at the surface.

A good reference for interpretation of imagery in mid latitudes is: Images in Weather Forecasting, edited by M.J. Bader, G.S. Forbes, J.R. Grant, R.B.E. Lilley, and A.J. Waters. Cambridge University Press, Cambridge, 1995.

Receiving Satellite Transmissions

I don't know very much about receiving satellite images. All I can offer, really, are the few pointers to better information listed below. I may, at some point, read them, and write some sort of a summary here.

Note: I know nothing about the quality of the services offered by the companies to which I link here. I merely know of their existence. If you are interested in purchasing their products it is up to you to investigate those I list here and search for others.

Ordering Archived Images

When images aren't available in online archives, a last resort is to order from the appropriate agency. I know very little about this (and have never done it), but I provide some links here for those who wish to explore.

Image and Movie File Formats

Dennis Chesters's GOES Data on the Internet - A Tutorial has more detailed information about images formats than I do, along with some other interesting information.

basically Lempel-Ziv compression, so there is no loss of quality
a slightly lossy, complicated compression algorithm - the files are smaller than GIFS, they can go above 8 bits but with weather images they usually don't. There is a slight loss of quality in the image.
a raster image format (inefficient) that is often used for scientific purposes because it can facilitate the storage of accurate data. One may need to download a viewer in order to view TIFF images. Many viewers only view a subset of correct TIFF images, and give errors otherwise. A page on the TIFF format is available.
a very lossy movie format. These are usually 320*200 resolution, and quality is degraded from that low resolution due to the compression. One may need to download a viewer in order to view MPEG movies. If you use Windows 95 and Internet Explorer, you should already have Media Player, which plays MPEGs. Otherwise, if you don't have one already, you will need to download an MPEG Viewer. The MPEG.ORG site has lots of information and viewers too.
a rarely used image format that I don't know much about.

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