The present-day series of operational Metsats can trace its inception to the launch of TIROS-M on January 23, 1970. Also called ITOS (for Improved TIROS Operational System), it included several vidicon cameras and an IR radiometer sensing between 3.4-4.2 Ám. The first of the NOAA series (TIROS 2 to 5) followed this initial satellite. Here is a typical image, showing the eastern U.S., made by the NOAA-4 Very High Resolution Radiometer (VHRR), operating in the near-IR region.
A new series in this generation began with the launch of TIROS-N on October 13, 1978. This satellite was the first in that series to carry the AVHRR (described on page 14-2), along with the first sounder, TIROS Operational Vertical Sounder (TOVS), designed to profile temperature and water vapor. The TOVS is actually a three instrument complex: the High Resolution IR Sounder (HIRS-2), with 20 channels; the Stratospheric Sounding Unit (SSU), with three channels near 15 Ám, and the Microwave Sounding Unit (MSU), a passive scanning microwave spectrometer with four channels in the 5.5 Ám interval.
These instruments are the mainstays of the subsequent NOAA-6 (launched on June 27, 1979) through NOAA-15 (May 1998) Metsats. Even-numbered NOAA Metsats have North to South equatorial crossing times near 7:30 A.M. and have orbital repeat periods (re-occupy approximately the same paths) of four to five days. The odd-numbered ones cross the equator from North to South at night (2:30 A.M.) and have eight-nine day repeat periods. NOAA strives to keep as many as four satellites in this series operational at any one time.
The thermal bands on AVHRR can generate temperature "maps" of water bodies, both oceans and lakes. Here is a thermal image of the temperature in early Fall in the five U.S. Great Lakes:
Here is a NOAA-9 AVHRR image in the visible region of Hurricane Gloria, as it neared the East Coast on September 27, 1997:
Like most multi-channel systems, we can combine different AVHRR-band images into color composites, as demonstrated by this NOAA-14 rendition of Hurricane Fran on September 4, 1996:
The NOAA daily images are compiled and displayed in different formats. Here is a NOAA-14 image taken on June 26, 2000 that covers European Russian eastward into Siberia.
The NOAA series also began the important task of looking at the distribution of ozone in the troposphere. TOMS (described later) and the SBUV (Solar Backscatter UV) are the principal instruments. Here are measurements made for two periods in 1990.
The latest in the NOAA group, NOAA-15, has these instruments: AVHRR/3; AMSU A & B (sounders); HIRS (an infrared sounder); SEN (Space Environmental Monitor); SAR (Search and Rescue); and DCS (Data Collection System. Its AVHRR now has a sixth band, at 1.6 Ám. The AMSU-A is capable of producing temperature profiles, as exemplified by this cross-section through Hurricane Bonnie.
ESA has only recently started to operate polar Metsats. EuMetSat, a consortium of 18 countries, launched MetOp-A on October 19, 2006. It is a big satellite, as shown below, which mounts 13 sensors. As examples of its products, observe the Visible image of clouds and a plot of nitrogen dioxide over Europe:
The former Soviet Union/CIS has launched more than 25 polar-orbiting satellites in its three Meteor Series, starting in March of 1969, and continuing through 1994. Other Metsats were part of their Kosmos series
China, too, is now in the Metsat field. Here is its polar-orbiting Feng Yun-1 (translates as "Wind Cloud") satellite (FY-1C); beneath is one of its regional images of China.
Next, we examine another class of Metsats that examine near full Earth discs from geostationary orbits.