A History of Scatterometry
Scatterometry has its origin in early radar used in World War II. Early
radar measurements over the oceans were corrupted by sea clutter (noise) and
it was not known at the time the cause of this clutter. It wasn't until the 1960s
that the noise in the radar signal was found to be the radar's response to
the winds over the ocean.
The first scatterometer flew as part of the Skylab missions in 1973 and
1974, demonstrating that spaceborne scatterometers were indeed feasible.
Then, from June to October 1978, the Seasat-A Satellite Scatterometer
(SASS) proved that accurate wind velocity measurements could be made
from space. In the 1990s, a single-swath (-beam) scatterometer was one of the
instruments to fly on the European Space Agency's ERS-1 (currently in
stand-by mode) and ERS-2 Remote Sensing Satellites, launched in July
1991 and April 1995 respectively.
The NASA Scatterometer (NSCAT) which launched aboard Japan's
ADEOS-Midori Satellite in August, 1996, was the first dual-swath,
Ku-band scatterometer to fly since Seasat. From September 1996, when the
instrument was first turned on, until premature termination of the
mission due to satellite power loss in June 1997, NSCAT performed
flawlessly and returned a continuous stream of global sea surface wind
vector measurements. Unprecedented for coverage, resolution, and
accuracy in the determination of ocean wind speed and direction, NSCAT
data has already been applied to a wide variety of scientific and
operational problems. These applications include such diverse areas as
weather forecasting and the estimation of tropical rain forest
reduction. Because of the success of the short-lived NSCAT mission,
future Ku-band scatterometer instruments are now greatly anticipated by
the ocean winds user community.
This image shows ocean surface wind speeds and directions over the
Pacific Ocean on September 21, 1996 as they were measured by the NASA
Scatterometer (NSCAT) which was onboard Japan's Advanced Earth Observing
Satellite (ADEOS). The background color indicates wind speed and the
white arrows show the direction of the wind. The strong Trade Winds
(red) blow steadily from the cooler subtropical ocean to the warm water
of the Intertropical Convergence Zone (ITCZ) located just north the
Equator. Instead of blowing in the north-south direction, the winds are
deflected westward by the Coriolis effect, an apparent force arising
from the rotation of the Earth on its axis. The air rises over the warm
water of ITCZ and sinks in the subtropics at the Horse Latitudes,
forming the Hadley Circulation. Both the convergence area at the ITCZ
and the divergence area at the Horse Latitudes are indicated by low wind
speed of blue color. In the sub-tropics and mid-latitudes, hurricanes (typhoons)
rely on some contribution from the Coriolis effect in order to develop
their characteristic spin (yellow spirals). Two typhoons are observed in
the western Pacific. Typhoon Violet is just south of Japan. After these
data were taken, Typhoon Violet struck the East Coast of Japan causing
damage and deaths. Typhoon Tom is located further east and did not make
Courtesy of NASA JPL.
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History of Scatterometry
Why is Scatterometry Important?