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CHANGES
IN POLAR ICE CONCENTRATIONS
The
polar regions are both dynamic and vitally important to the
well being of the planet. But research and data collection
of Arctic Ocean ice isn't easy. That's why so much ice and
polar research has turned to space based measuring systems
in recent years. Not only are the risks to and limitations
of in situ human exploration greatly mitigated, but also new
wide scale observation techniques become possible from a perch
high above the planet.
That's
leads us to Aqua's role in studying ice. Of the many jobs
assigned to this new Earth observatory, looking at changing
sea ice conditions is one of the most cognitively tangible.
By using data collected with a number of different satellites
from 1978 to 1998, scientists have been able to stitch together
a quality- controlled record of sea ice around the poles.
The data used to create these visualizations come from different
instruments onboard a group of satellites: the scanning multi-channel
microwave radiometer on board the Nimbus 7 satellite, and
the special sensor microwave imagers on board to the Defense
Meteorological Satellite Program's F8, F11, and F13 satellites.
The following two visualization sequences present average
annual polar ice concentrations for the nineteen-year period
studied. Looking at each pole in these visualizations we start
by looking at displays of average ice concentrations in March,
the annual maximum. As the visualization progresses, we see
the quantity of ice diminish as the calendar heads towards
September, the annual minimum. The cycle oscillates between
maximum and minimum as the calendar advances, ice building
up around the poles in winter and receding as summer approaches.
The research behind these images presents certain intellectual
challenges, too. Part of the work to make this kind of exploration
useful included efforts to account for atmospheric interference,
calibration of multiple instruments, and changes in computer
processing systems over the two decades since the data started
to be collected. With the launch of Aqua, experts hope to
continue adding to the historical record of sea ice changes
over time.
THE
ESSENTIAL BLANKET OF ICE
The
polar caps not only hold much of the planet's total fresh
water, but also play an important role in regulating the Earth's
temperature. One of the most important characteristics that
describes the poles is called albedo. It's a measure of how
much radiation, or light, is reflected from a body. Similar
to how a white shirt helps keep a person cooler in the summer
than a black shirt, the vast stretches of polar ice covering
much of the planet's top and bottom reflect large amounts
of solar radiation falling on the planet's surface. Were the
ice caps to appreciably recede, sunlight that otherwise would
have been reflected back into space would get absorbed by
the darker, denser mass of ocean and land beneath. As light
is absorbed, the environment heats up, thus intensifying a
feedback loop: a warmer planet yields more ice melting thus
an even warmer planet.
This animation provides a close-up perspective of the relationship
between ice and solar reflectivity. As glaciers, the polar
caps, and in this case, icebergs melt, less sunlight gets
reflected into space. It is instead absorbed into the oceans
and land, thus raising the overall temperature, and adding
energy to a vicious circle.
Of the many concerns voiced by scientists who study global
warming trends, rising ocean levels is one of the most dramatic.
An average rise in global ocean levels of just a few inches
could have devastating effects on coastal towns, cities, and
ecosystems. Why then is even the slightest risk of a shrinking
polar cap not sounding alarms all across the world's lowland
regions?
For ice found in the frozen northern ocean, the issue comes
down to a simple principle proved thousands of years ago by
the Greek philosopher and scientist Archimedes. He showed
that a body, in this case the floating ice of the North Pole
region, immersed in a fluid, is buoyed up by a force equal
to the weight of the displaced fluid. In other words, since
the northern pack ice is already floating, its melting would
not independently cause ocean levels to rise. However, the
attending planetary conditions necessary to facilitate polar
melting would likely have other enormous effects on the environment,
including the likely melting of the Greenland ice sheet and
the southern polar sheet. As the ice over Greenland and Antarctica
is NOT floating, a corresponding rise in the world's sea level
would almost certainly result if that ice melted.
Several of the instruments onboard Aqua will be watching for
signs of change in the planet's icy regions. Similarly, as
a research platform designed to study the Earth in systemic
terms, Aqua will also be monitoring larger planetary forces
that might influence polar ice in an effort to provide the
best possible information not only about how our home planet
works, but also how it's influenced by people.
CLIMATE
AND WEATHER: RELATED BUT DIFFERENT
They're
not the same, but weather and climate are fundamentally linked.
Weather describes the meteorological conditions of a particular
place at a particular time. Climate is the term used for characterizing
the typical, or at least average, conditions for a particular
place.
Here's an example: much of the U.S. showed unusually warm
temperatures throughout the autumn and winter of 2001. Scientifically
speaking, these were anomalies in weather patterns; the unusually
high thermometer readings throughout those months simply showed
a greater than average temperature along with lower than average
precipitation levels.
But those sunny days when people expected to be wearing winter
coats were descriptions of weather. Only if they started to
add up year after year, changing long held expectations for
what those months ought to bring would they begin to describe
climate. Say that year after year the eastern seaboard scarcely
cooled in what had traditionally been autumn months, with
rain and snow falling infrequently. In this case we would
be speaking of the area's climate, or the average conditions.
Said another way, climate is a function of weather patterns
taken over time.
SIBLING
SPACECRAFT ON ORBIT
Aqua
was formerly named EOS PM, a moniker intended to describe
its institutional heritage. EOS stands for Earth Observing
System; PM designates that the satellite will fly in an orbit
that positions it over the Earth so as to be tracked to an
afternoon transit during the daylight phase of its swing around
the planet. Its slightly older sibling is called Terra. It
too had a former name, that being EOS AM. As you might infer,
Terra makes its daylight pass during the morning.
The fact that Aqua and Terra follow orbital paths that have
them pass by individual locations at different times is significant.
Things change throughout the day on Earth, and the ability
to make measurements of one place on the globe at different
times is a powerful analytic tool. Sunlight on plants promotes
photosynthesis, surface temperatures shift, and atmospheric
characteristics shift. By adding the measuring capabilities
of Aqua to Terra's already operational systems, experts hope
to be able to better understand how natural processes on Earth
react to cyclical changes throughout the day.
TAKING
THE A-TRAIN
The
name "A-Train" comes from a planned sequence of
satellites on orbit, starting with Aqua and ending with Aura.
These two, and the three or more that will separate them are
all part of a spacecraft convoy, each part of the growing
fleet of Earth watching satellites that compose the Earth
Observing System.
The idea of building a fleet of vehicles is similar to the
motivation for having a number of different instruments onboard
individual satellites. By turning the eyes of multiple instruments
onto individual planetary events, scientists can study various
aspects of planetary functions in systemic terms. Different
instruments on different orbiting platforms give scientists
layers of flexibility to pursue answers about the Earth.
This kind of satellite navigation is called Enhanced Formation
Flying. It allows for highly precise cross calibration of
instruments as well as near-time multi-instrument measurements.
Enhanced Formation Flying (EFF) employs highly sophisticated
software systems, including so-called "fuzzy logic"
algorithms to resolve navigational and operational conflicts
that inevitably occur in flight. Some of the benefits of flying
satellites in formation come in the area of risk management.
In the future, by using fleets of less expensive, less complex
satellites in place of singularly large, highly sophisticated
platforms, a catastrophic failure does not necessarily cause
irreparable harm to an overall mission. Further, by flying
a suite of sensors in formation, researchers can essentially
create one enormous "virtual" satellite by integrating
the individual data from each smaller instrument.
AN
ENTERPRISE, AN ADVENTURE
Aqua
is just one component of NASA's growing Earth Observing System,
an integrated fleet of satellites and data collection procedures
designed to study the Earth in terms of conjoined, interdependent
processes.
Space offers a useful and powerful perspective for gathering
information about natural and human-induced change around
the world. It's not feasible to study changes in the oceans,
the atmosphere, or life on Earth in global terms without looking
back at the Earth from space.
The Earth Observing System, or EOS, is part of the larger
Earth Science Enterprise. ESE continues to develop new technologies
and applications aimed at managing natural hazards, civil
planning, natural resource management, and much more. In the
near term, the program has set its sights on a better understanding
of global climate change. But in the long term, this evolving
and exciting way of studying how the living Earth works offers
great advances in a number of important fields.
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