Press Release

NASA’s SEASAT: At 25, Remembering a Trendsetting Seafaring Satellite

By SpaceRef Editor
June 28, 2003
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It only skippered the seas of space for a mere three months, but just
as Gilligan’s "three-hour tour" has continued on in syndication for
decades, a salty satellite launched to study the oceans 25 years ago
this week by NASA’s Jet Propulsion Laboratory, Pasadena, Calif., is
living on through the many missions it has spawned.

Seasat’s tale began in the 1970s when a group of engineers and
scientists at JPL began work on an experimental satellite to study
Earth and its seas, using technologies being developed to study other
planets. The satellite’s trip started from the not-so-tropic port of
Vandenberg Air Force Base, Calif., on June 26, 1978, aboard an
Atlas-Agena rocket. The five "passengers" that set sail that day
aboard Seasat included three prototype radar instruments and two
radiometers.

Seasat’s "weather" got rough 106 days later, when a malfunction
unexpectedly ended the mission. Yet during its brief life Seasat
collected more information about the oceans than had been acquired in
the previous 100 years of shipboard research. It established
satellite oceanography and proved the viability of imaging radar for
studying our planet. Most importantly, it spawned many subsequent
Earth remote sensing satellites and instruments at JPL and elsewhere
that track changes in Earth’s oceans, land and ice. Its advances were
also subsequently applied to missions to other planets.

"Seasat served to vault Earth science to where it is today, advancing
the study of such diverse disciplines as land and sea surface
topography, ice sheet and land movement, and sea surface winds," said
Dr. Frank Carsey, JPL research scientist. "It greatly advanced our
understanding of the El Nino and La Nina climate phenomena. It’s
astonishing to think such a short mission could have such a tremendous
impact."

"Seasat had a major impact on future mission planning at NASA and
elsewhere," said Tony Spear, Seasat sensor manager. "Its prototype
radars and altimeter were precursors for many of today’s more powerful
Earth observation satellites."

Seasat’s experimental instruments included a synthetic aperture radar,
which provided the first-ever highly detailed radar images of ocean
and land surfaces from space; a radar scatterometer, which measured
near-surface wind speed and direction; a radar altimeter, which
measured ocean surface and wave heights; and a scanning multichannel
microwave radiometer measuring surface temperatures, wind speeds and
sea ice cover.

In oceanography, Seasat gave us our first global view of ocean
circulation, waves and winds, providing new insights into the links
between the ocean and atmosphere that drive our climate. For the
first time, the state of an entire ocean could be seen all at once.
Seasat’s altimeter mapped ocean topography, allowing scientists to
determine ocean circulation and heat storage. The data also revealed
new information about Earth’s gravity field and the topography of the
ocean floor. Since Seasat, advanced ocean altimeters on JPL’s
Topex/Poseidon and Jason missions have been making precise
measurements of sea surface height used to study climate phenomena
such as El Nino and La Nina. Ocean altimetry has since become part of
weather and climate models, ship routing, marine mammal studies,
fisheries management and offshore operations.

Seasat’s synthetic aperture radar monitored the global surface wave
field and revealed a wide spectrum of oceanic and atmospheric
phenomena from current boundaries to eddies.

Seasat’s scatterometer gave us our first real-time global map of the
speed and direction of ocean winds, which drive waves and currents and
are the major link between the ocean and atmosphere. The technology
was later used on JPL’s NASA Scatterometer and is now flying on JPL’s
Quikscat spacecraft and its SeaWinds instrument on Japan’s Midori 2
spacecraft. The data help forecasters predict hurricanes, tropical
storms and El Ninos.

Seasat’s oceanographic mission also studied sea ice and its role in
controlling Earth’s climate. Its synthetic aperture radar provided
the first high-resolution images of sea ice, measuring its movement,
deformation, age and thickness. Today, synthetic aperture radar and
scatterometers are both used to monitor Earth’s ice from space.

Beyond the oceans, Seasat’s synthetic aperture radar provided
spectacular images of Earth’s land surfaces and geology. Seasat data
was used to pioneer radar interferometry, which can pinpoint land
surface changes such as those created by earthquakes, and to measure
land surface topography. Three JPL Shuttle Imaging Radar experiments
flew on the Space Shuttle in the 1980s/1990s. In 2000, JPL’s Shuttle
Radar Topography Mission used the technology to create the world’s
most detailed topographic measurements of more than 80 percent of
Earth’s land surface. Beyond Earth, the technology was used on JPL’s
Magellan mission, which mapped 99 percent of the previously hidden
surface of Venus, and the Titan radar onboard the JPL-built and
managed Cassini orbiter to Saturn.

Among the international missions with heritages tracing to Seasat are
the current Japanese Earth Resources Satellite 1, the Canadian/U.S.
Radarsat and the European Space Agency’s Remote Sensing Satellites.

For more information on Seasat, visit:
http://www.jpl.nasa.gov/flash/seasat/intro.cfm. JPL is a division of the
California Institute of Technology, Pasadena.

SpaceRef staff editor.