Exploring the Unknown - NASA's History Office

EXPLORING THE UNKNOWN 161
and the Weather Bureau were more free to think about experimental satellites to test out
new instruments that might be incorporated into future generations of operational satellites.
Nimbus 1, launched April 28, 1964, experienced a number of problems and operated
for only a month; Nimbus 2, launched May 15, 1966, was much more successful, testing
out improved cameras. NASA also tested meteorological satellite technology as part of the
Applications Technology Satellite (ATS) project to orbit experimental geosynchronous
satellites (used for communications experiments as well as meteorological ones). In
December 1966 and November 1967, ATS-1 and -3 explored the possibility of observing
weather with line scan imagers, a possibility conceived by Vernon Soumi, a professor at the
University of Wisconsin; the resulting continuous coverage (images of the full Earth disc
every thirty minutes) proved extremely valuable for tracking storms and even showed
short-lived cloud patterns correlated to tornadoes. 31 Continuous coverage from geosynchronous
orbit made it possible to observe the motion of clouds and deduce wind speed
at the level of the clouds—a significant step toward the three-dimensional quantitative
data meteorologists wanted. Three other satellites in the series, ATS-2, -4, and -5, also carried
meteorological experiments, but all suffered launch problems. 32 ATS-6, launched in
May 1974, carried a new cloud-imaging radiometer along with a more powerful transmitter
that made it possible for anyone with an easy-to-build ground station to receive the
images. 33
While the ATS program tested ideas for weather satellites in geosynchronous orbit,
the Nimbus program continued to test advanced instruments in low-Earth orbit, with five
launches between 1969 and 1978. Nimbus 3, launched April 1969, carried five new sensors.
These included the first sounding instruments using remote sensing to furnish measurements
of temperature and other variables at different levels of the atmosphere for
providing numerical data for climate models. The sounding instruments on Nimbus 3
measured temperature, water vapor, and ozone content of various atmospheric levels;
later Nimbus satellites carried sounding instruments to measure other variables. The sensors
worked well, but the data proved much less useful for weather prediction than scientists
had expected. Meteorologists had hoped that data on temperature, wind speed, and
other factors could be plugged into a model of how the atmosphere worked to provide
weather predictions. Satellite sounding instruments provided much of the data needed
with reasonable accuracy, but existing climate models were not designed to assimilate
these data easily. Meteorologists discovered that they needed to perform much more
research before they could use data acquired by satellite to improve the accuracy of weather
predictions. 34
In August 1966, the Weather Bureau stated the following as its objectives for an operational
satellite system: “(1) [t]he establishment and maintenance of a satellite system to
obtain global observations on a regular basis, (2) meteorological observations from synchronous
altitude, and (3) global observations of atmospheric structure needed for
numerical weather forecasting.” [II-6] The first objective was met by continuing improvements
in the TIROS series of low-altitude satellites, which were flown from 1966 to 1969.
NASA launched an Improved TIROS Operational Satellite (ITOS) in January 1970. 35
31. The ATS cameras provided pictures every thirty minutes, compared to once or twice a day from the
TIROS Operational System. For a discussion of the usefulness of continuous coverage, see W.L. Smith et al., “The
Meteorological Satellite: Overview of 25 Years of Operation,” Science 231 (January 31, 1986): 455–62.
32. Hill, Weather from Above, pp. 23–26, 29–32.
33. Ibid., pp. 33–35.
34. James C. Fletcher to Stuart Eizenstat, “Possible Initiatives,” February 16, 1977, suggests that NASA
hoped that sounding instruments would lead to a major new research initiative. Pamela E. Mack, “Cloudy Seeing:
Developing New Sensors for Weather Satellites,” paper presented at the Society for the History of Technology’s
annual meeting, London, England, August 1996.