Trailblazer Sea Satellite Marks its Coral Anniversary

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 PHONE 818-354-5011
http://www.jpl.nasa.gov

Alan Buis
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0474
alan.buis@jpl.nasa.gov

News feature: 2013-208 June 27, 2013

Trailblazer Sea Satellite Marks its Coral Anniversary

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.php?release=2013-208&cid=release_2013-208

"The true worth of a man is not to be found in man himself, but in the colours and
textures that come alive in others."

- Albert Schweitzer

History tends to look fondly upon trailblazers, even if they don't necessarily stick around.
From musicians and actors to politicians and inventors, our lives are immeasurably
enriched by the contributions of visionaries who left us.

So when NASA's Jet Propulsion Laboratory, Pasadena, Calif., launched an
experimental satellite called Seasat to study Earth and its seas 35 years ago this week,
only to see the mission end just 106 days later due to an unexpected malfunction, some
at the time may have looked upon it as a failure. But this spunky satellite, which is still in
orbit, shining in the night sky at magnitude 4.0, continues to live on through the many
Earth and space observation missions it has spawned.

Seasat's tale began in 1969, when a group of engineers and scientists from multiple
institutions convened at a conference in Williamstown, Mass., to study how satellites
could be used to improve our understanding of the ocean. Three years later, NASA
began planning for Seasat, the first multi-sensor spacecraft dedicated specifically to
observing Earth's ocean. A broad user working group from many organizations defined
its requirements. JPL was selected to manage the project, and numerous other NASA
centers and government and industry partners participated. On the night of June 26,
1978, Seasat was launched from California's Vandenberg Air Force Base aboard an
Atlas-Agena rocket, carrying with it three prototype radar instruments and two
radiometers.

During its brief life, Seasat collected more information about ocean physics than had
been acquired in the previous 100 years of shipboard research. It established satellite
oceanography and proved the viability of several radar sensors, including an 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 ocean, land and ice, including many currently in orbit or in development. Its
advances were also subsequently applied to missions to study other planets.

Post-Seasat NASA program manager Stan Wilson said Seasat demonstrated the
potential usefulness of ocean microwave observations. "As a result, at least 50 satellites
have been launched by more than a dozen space agencies to carry microwave
instruments to observe the ocean. In addition, we have two continuing records of critical
climate change in the ocean that are impacting society today: diminishing ice cover in
the Arctic and rising global sea level. What greater legacy could a mission have?"

"Seasat flew long enough to fully demonstrate its groundbreaking remote sensing
technologies, and its early death permitted the limited available resources to be
marshaled toward processing and analyzing its approximately 100-day data set," said
Bill Townsend, Seasat radar altimeter experiment manager. "This led to other systems,
both nationally and internationally, that continued Seasat's legacy, enabling Seasat
technologies to be used to better understand climate change."

Seasat's experimental instruments included a synthetic aperture radar (SAR), 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 height, wind speed and wave heights;
and a scanning multichannel microwave radiometer that measured atmospheric and
ocean data, including wind speeds, sea ice cover, atmospheric water vapor and
precipitation, and sea surface temperatures in both clear and cloudy conditions.

On June 28, the Alaska Satellite Facility will release newly processed digital SAR
imagery from Seasat. The imagery, available for download at http://www.asf.alaska.edu
, will enable scientists to travel back in time to research the ocean, sea ice, volcanoes,
forests, land cover, glaciers and more. Before now, only about 20 percent of Seasat
SAR data had been processed digitally.

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, which used pulses of microwave radiation to measure the
distance from the satellite to the ocean surface precisely, mapped ocean surface
topography, allowing scientists to demonstrate how sea surface conditions could be
used 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.

"The short 100-day Seasat mission provided a moment of epiphany to remind people
that the vast ocean is best accessed from space," said Lee-Lueng Fu, JPL senior
research scientist and project scientist for the NASA/French Space Agency Jason-1
satellite and NASA's planned Surface Water and Ocean Topography mission.

Seasat inspired a whole generation of scientists. "I decided to take a job offer at JPL
fresh out of graduate school because I was told that the future of oceanography is in
satellite oceanography and the future of satellite oceanography will begin with Seasat at
JPL," said JPL oceanographer Tim Liu. "I did not plan to stay forever, but I have now
been here more than three decades."

Since Seasat, advanced ocean altimeters on the NASA/European Topex/Poseidon and
Jason missions have been making precise measurements of sea surface height used to
study climate phenomena such as El Niño and La Niña. The newest Jason mission,
Jason-3, is scheduled to launch in 2015 to continue the 20-plus-year climate data
record. Satellite altimetry has been used to improve weather and climate models, ship
routing, marine mammal studies, fisheries management and offshore operations.
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. A scatterometer is a microwave radar sensor used to measure
the reflection or scattering effect produced while scanning the surface of Earth from an
aircraft or a satellite. The technology was later used on JPL's NASA Scatterometer,
Quikscat spacecraft, SeaWinds instrument on Japan's Midori 2 spacecraft and the
OSCAT instrument on India's Oceansat-2. It will also be used on JPL's ISS-RapidScat
instrument, launching to the International Space Station in the spring of 2014. Data from
these scatterometers, including three scatterometers launched by the European Space
Agency, help forecasters predict hurricanes, tropical storms and El Ninos.

Seasat's microwave radiometer, which subsequently flew on NASA's Nimbus-7 satellite,
led to numerous successful radiometer instruments and missions used for
oceanography, weather and climate research. Radiometers measure particular
wavelengths of microwave energy. The Seasat radiometer's heritage includes the
Special Sensor Microwave Imager instruments launched on United States Air Force
Defense Meteorological Satellite Program satellites, the joint NASA/Japanese
Aerospace Exploration Agency (JAXA) Tropical Rainfall Measuring Mission microwave
imager, the Advanced Microwave Scanning Radiometer (AMSR)-E that flew aboard
NASA's Aqua spacecraft, JAXA's current AMSR-2 instrument, and numerous other
radiometers launched by Europe, China and India. The radiometer, scatterometer and
SAR for NASA's Soil Moisture Active Passive mission to measure global soil moisture,
launching in 2014, also draw upon Seasat's heritage.

By simultaneously flying a radiometer with a radar altimeter, Seasat demonstrated the
benefit of using radiometer measurements of water vapor to correct altimeter
measurements of sea surface height. Water vapor affects the accuracy of altimeter
measurements by delaying the time it takes for the altimeter's signals to make their
round trip to the ocean surface and back. This technique has been used on all
subsequent NASA/European satellite altimetry missions.

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

"It's hard to imagine where we would be without the radiometer pioneered on Seasat,
but certainly much further behind in critical Earth observations than we are now," said
Gary Lagerloef of Earth & Space Research, Seattle, principal investigator of NASA's
Aquarius mission to map ocean surface salinity. The Aquarius radiometer and
scatterometer also trace their heritage back to Seasat.

Seasat's SAR monitored the global surface wave field and revealed many oceanic- and
atmospheric-related phenomena, from current boundaries to eddies and internal waves.

Beyond the ocean, Seasat's SAR provided spectacular images of Earth's land surfaces
and geology. Seasat data were used to pioneer radar interferometry, which uses
microwave energy pulses sent from sensors on satellites or aircraft to the ground to
detect land surface changes such as those created by earthquakes, and 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. Today, the technology is being used on JPL's
Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) airborne imaging radar
system for a wide variety of Earth studies. Among the international SAR missions with
heritages tracing to Seasat are the Japanese Earth Resources Satellite 1 and Advanced
Land Observing System 1, the Canadian/U.S. Radarsat 1 and the European Space
Agency's Remote Sensing Satellites. The technology will also be used on NASA's
planned Surface Water and Ocean Topography mission, planned for launch in 2020.

Paul Rosen, JPL project scientist for a future NASA L-band SAR spacecraft currently
under study, said Seasat's demonstration of spaceborne repeat-pass radar
interferometry to measure minute Earth surface motions has led to a new field of space
geodetic imaging and forms the basis for his new mission.

"Together with international L-band SAR sensors, we have the opportunity in the next
five years to create a 40-year observation record of land-use change where overlapping
observations exist," Rosen said. "These time-lapse images of change will provide
fascinating insights into urban growth, agricultural patterns and other signs of human-
induced changes over decades and climate change in the polar regions."

Beyond Earth, Seasat 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.

Seasat was managed by JPL for NASA, with significant participation from NASA's
Goddard Space Flight Center, Greenbelt, Md.; NASA's Wallops Flight Facility, Wallops
Island, Va.; NASA's Langley Research Center, Hampton, Va.; NASA's Glenn Research
Center, Cleveland, Ohio; Johns Hopkins University Applied Physics Laboratory, Laurel,
Md.; Lockheed Missiles and Space Systems, Sunnyvale, Calif.; and NOAA,
Washington, D.C.

For more on Seasat, visit: http://podaac.jpl.nasa.gov/SeaSAT and
http://www.jpl.nasa.gov/multimedia/seasat/intro.html . JPL is a division of the California
Institute of Technology, Pasadena.

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