Ever since the dawn of the space age, we have grown accustomed to
the “big picture” imagery of far-distant planets and moons, which have
come to be studied as whole entities. Increasingly, astronomers are
interpreting data from telescopes and space probes to identify the
features of other bodies in space.

But what of our own planet? Actually, a Canadian Earth observation
satellite, RADARSAT-1, is being used to develop a better understanding
of the globe from pole to pole. Imagery produced by this renowned
leading-edge Earth observation satellite is helping to answer crucial
scientific questions about the rate and extent of global climate
change. Indeed, RADARSAT-1 data collected so far show that Antarctica,
one of the most remote parts of our world, is changing and possibly in
response to changing climate. This is important because the Antarctic
ice cap is a huge reservoir of fresh water and changes in that
reservoir directly change global sea level.

Following its launch in 1995, RADARSAT-1 embarked in 1997 on the
first Antarctic Mapping Mission. This scientific initiative was a
collaboration between the Canadian Space Agency (CSA), NASA, the Byrd
Polar Research Center at The Ohio State University, California’s Jet
Propulsion Laboratory, Colorado’s Vexcel Corporation and the Alaska
SAR Facility.

Ken Jezek, Principal Investigator of the mission, at the Byrd
Center, developed an unprecedented high-resolution mosaic map of the
entire frozen continent in 1999. The mission produced the first
complete image of the continent, providing a baseline from which
future changes could be measured. It also demonstrated the capacity of
RADARSAT-1 to measure ice flow, using its Synthetic Aperture Radar
(SAR) in an interferometric mode (InSAR), over several repeat passes.

The Antarctic Mapping Mission revealed features of Antarctica in a
way that great polar explorers of the past, like Shackleton, Scott and
Amundsen, could only dream of. Images produced during the mission
showed the rocky tops of volcanoes surrounded by the West Antarctic
ice sheet, giant fields of snow dunes that zigzag across East
Antarctica, and even the surface outline of subglacial Lake Vostok.
These images also revealed that a network of ice streams, one ice
stream of which is 800-kilometres long and reaches speeds up to one
kilometer per year, was transporting close to 80 cubic kilometers of
ice into the sea every year.

In November 2000, another Antarctic Mapping Mission was completed.
This second mission aimed at producing even higher resolution image
mosaics of Antarctica north of 80 degrees and using radar
interferometry to obtain the first complete measurement of surface
velocity around the perimeter of the continent. This new look at
Antarctica will help scientists better understand the forces that
drive the ice sheet and the response of the ice sheet to climate
change.

Although it will take several years to process the entire data set
captured during this second mission, images have already been compared
with earlier data and the comparisons graphically portray the retreat
of ice shelves in the Antarctic Peninsula which many scientists
consider to be a consequence of global warming. But that is not the
whole story. With the continental scale observations from these two
scientific missions, it is now possible for the first time to inspect
a variety of different environmental regimes and the local behavior of
the ice sheet margin. Not surprisingly, the situation now seems more
complex.

Early analyses show that in just three years the Amery Ice Shelf
has advanced five kilometres, while the Shirase Glacier, located in
the Indian Ocean sector of the continent, has retreated twelve
kilometres, and an enormous tabular iceberg (10,915 km2) calved from
the Ross Ice Shelf. Is this variability due to the forces of external
climate on the great ice sheet or is it due to natural and episodic
instabilities that arise from the forces that control complex glacier
flow? The new velocity measurements from the second mission will help
answer that question. For example, initial analysis of InSAR data of
the Lambert Glacier, one of the world’s longest ice streams, reveal a
sinuous network of tributary glacier that eventually feed the Amery
ice shelf. Understanding the interplay between these tributaries as
well as tributaries within other similar systems in East and West
Antarctica is of prime scientific importance in understanding how ice
is transported through the ice sheet and out into the sea.

Canada’s RADARSAT-1 has played a major role in these Antarctic
missions and is a technological success story. Traveling at a speed of
close to 7 kilometres a second, in a near-circular polar orbit, about
800 kilometres above the surface of the Earth, it goes around the
Earth once every 100 minutes, completing fourteen orbits per day.
RADARSAT has the unique ability to train its synthetic aperture radar
on the Earth, penetrating cloud cover and the shroud of darkness. This
is a special advantage in the polar regions, where the darkness of the
winter night is measured not in hours, but in months. SAR is
particularly well-suited for providing high-resolution images of
subtle differences in surface features, such as ice and geological
formations. RADARSAT can be rotated, and is equipped with tape
recorders, so that it can collect data, before downloading it to
ground stations.

But RADARSAT is also a human success story. The way the satellite
was handled by its Canadian operators during these two scientific
missions is a testimony to their resourcefulness and ingenuity. The
Canadian Space Agency performed the difficult feat of rotating
RADARSAT 180 degree during the first Antarctic Mapping Mission, in
order to provide the needed angle of incidence for Antarctic imaging.
During the follow-on mission, the Canadian Space Agency controlled the
800-kilometre orbit of RADARSAT-1 in a very precise manner by
periodically firing the spacecraft’s onboard thrusters so as to
position the satellite within a few hundred meters of the same
position occupied 24 days earlier. All the while, CSA coordinated the
capture and downlinking of data to a network of stations distributed
around the world.

The two scientific missions have produced a new baseline dataset
for the scientific community one that will prove invaluable in
monitoring the state of the Antarctic ice cap. This same leading-edge
technology is also being brought to bear on studies of polar ice in
Canada’s Arctic region and has been used to produce the first, high
resolution radar map of all of Canada.

RADARSAT-1 is being exploited beyond its nominal lifetime.
RADARSAT-2, currently under construction for the Canadian Space Agency
by MacDonald Dettwiler and Associates and scheduled for launch in
2003, will build on a legacy of service to commercial, government and
academic users. These unique spacecraft, and the team of highly
skilled professionals operating them, are an important resource,
providing key data for clients in the fields of mapping, geology,
oceanography, ice surveillance, agriculture, natural resources
exploration, supporting disaster and relief efforts worldwide and
helping scientists improve their understanding and measure the effects
of global warming on our planet Earth.

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