We switch now to consider the second general class of Metsats: those in geosynchronous orbit. That orbit is achieved when the spacecraft is "parked" above the Earth at 35,800 km (22,300 miles) and is moving along a circular path around the planet at approximately 11052 km/hr (6802 mph). A point on the Equator that remains directly underneath is traveling at ~1667 km/hr or 1042 mph. At these speeds there is no relative motion differences, so that the observing satellite is synchronously locked into a geostationary position above the hemisphere it is intended to view and (unless it drifts) will always view the same scene.
Much of the imagery shown on TV News Weather segments comes from geostationary satellites. Launched on December 7, 1966, the first such satellite was the Applications Technology Satellite-1 (ATS-1), which employed the Spin Scan Cloud Camera (SSCC) to obtain visible images of the western hemisphere. Here is the first image obtained by ATS-1, which was initially centered above Eduador (but drifted west), in which several cyclonic disturbances are present in the scene:
The value of synoptic coverage over short time spans was quickly proven by images such as these:
Rapid improvement in vidicon technology led to the first color system, the Multicolor Spin Scan Cloud Camera (MSSCC), on ATS-3 (launched November 5, 1967), producing striking portraits of entire continents such as this view of South America:
The beginning of an operational system dates to May 17, 1974, with the launch of the first of two Synchronous Meteorological Satellites (SMS). Each SMS carried, as its principal sensor, the Visible Infrared Spin Scan Radiometer (VISSR). These were predecessors to NOAA's Geostationary Operational Environomental Satellite (GOES) series-the kingpin of present day geosynchronous systems, covering the western hemisphere. Here is a photograph of GOES-1 on the ground awaiting mating to its launch rocket:
GOES-1 arrived in a geostationary orbit at 135° W, soon after its launch on October 16, 1975. Others have since been launched at two to three year intervals . Meteorologists refer to the satellites covering the Atlantic Ocean and the eastern U.S. as GOES-East (located above the equator at 75°W longitude), and those over the Pacific as GOES-West (at 135°W longitude). Together, they provide coverage of both the Atlantic and Pacific, as shown in this drawing which also illustrates the full disk nature of the view:
A more advanced series of GOES spacecraft, called the GOES-IM group, began with GOES-8, shown here as an artist's drawing:
To cover the entire Earth, four GOES would be needed. However, other parts of the world are monitored by other systems (see next page). As of mid-2005, GOES-8 has been decommissioned, GOES-9 is in backup status, GOES-10 (West) and GOES-12 (East) are operating, and GOES-11 also is in orbit but in storage until GOES 10 fails.
Starting with GOES-8 (April 13, 1994), the IMAGER operates all of the time, rather than providing periodic views. A second sensor, the SOUNDER, provides profile data through the atmosphere. To exemplify GOES imagery, we now show the first visible image (top) from GOES-1 on October 26, 1975 and the first test IR image (bottom) from GOES-9 on June 19, 1995 (that satellite failed early in its operational life):
These hemispherical images can be subdivided to concentrate on specific areas. Here are a GOES-8 (East) image that focuses on a large continental storm on March 20, 1994:
The GOES-8 sounder has a visible band and 18 thermal bands, which are sensitive to temperature variations related to CO2, ozone, and water vapor at different atmospheric levels. Each band is made into an image, to which colors are assigned, to identify thermal differences, as demonstrated in this panel of images taken on May 5, 1997.
Unusual color composites can be made from different channel images. Below on the top is a colorized rendition of the 6.7 µm channel image from GOES-8, which is sensitive to water vapor distribution, highlighting a big U.S. storm on March 20, 1994. Below it is a false color image made from Channel 6.7 µm = blue; 11 µm = green; Visible = red. This GOES-8 image displays Hurricane Hugo, as seen on September 21, 1989.
The GOES-NP group is scheduled to begin their launch sequence in 2006. An even more advanced satellite, GOES-S, may fly by 2012.
Various nations have now launched geostationary satellites. A complete listing is found online at this Colorado State website.