ICESAT To map Earth’s Ice Sheets

COLUMBUS, Ohio — The frozen wasteland of Antarctica’s McMurdo
Station may be about as far from the beaches of Ocean City, MD,
as anyone could get. But the same Ohio State University software
that mapped the sunny resort town last year will soon enable
researchers to study the area around McMurdo, and many other
icy parts of the world.

The mapping software is one of several contributions that
Ohio State is making to NASA’s
Ice, Cloud, and land Elevation Satellite (ICESat), said Bea
Csatho, senior research associate at Ohio
State’s Byrd Polar Research Center (BPRC).

Csatho heads the university’s ICESat team, which is working
with Robert Thomas, a scientist for EG&G Services at NASA’s Wallops Flight Facility,
Wallops Island, VA.

Currently set to launch on Jan. 11, 2003, ICESat will map
the Earth’s ice sheets using a radar-like system called lidar.
Short for "LIght
Detection And Ranging," lidar measures the time it takes
for light to reflect off the surface of an object. In this case,
The Geoscience
Laser Altimetry System (GLAS), the lidar system of the ICESat
satellite, will measure the size of ice sheets in the polar regions
to determine if they are growing or shrinking. If the ice sheets
are shrinking, then melting ice might cause global sea levels
to rise over time, and ICESat will attempt to gauge the extent
of such effects.

To make sure ICESat’s lidar system is calibrated properly,
NASA will have the satellite target a set of test sites during
the first three months of orbit. Chief among the duties of Csatho
and her colleagues is choosing and characterizing some of these
calibration sites.

One site is the McMurdo
Dry Valleys, the largest ice-free area in Antarctica. The
Dry Valleys make a good test site, Csatho said, because the area’s
proximity to McMurdo Station allowed researchers to collect precise
surface elevation data by using NASA’s
Airborne Topographic Mapper, a scanning lidar system. Those
results can be compared to ICESat’s data to see how well the
new lidar system is working.

The Dry Valleys area presents special challenges for lidar
measurements, Csatho explained. There, the exposed rock is very
dark, and the ice is very bright. That huge change in brightness
can cause the lidar system to make errors in measurement.

That’s what makes the Ohio State lidar mapping software ideal
for the job. Tony
Schenk, professor of civil
and environmental engineering and geodetic science, first
developed the software that fuses lidar data and aerial imagery
to automatically map areas of complex shape and elevation, such
as roads or cities. Impeyong Lee, a postdoctoral researcher at
BPRC, is helping Schenk adapt the software code for ICESat.

Tests in Ocean City in 2001 revealed that the software performed
well at mapping a complex city skyline, Lee said. As seen from
above, the up-and-down surface of roofs of varying heights presents
the same challenges as the bright and dark areas of the Dry Valleys.

Yushin Ahn, one of Schenk’s doctoral students, and Marcus
Dora, a visiting graduate student in cartography from the University
of Dresden in Germany, will create the maps that NASA scientists
and others will use to study the data in the future.

As ICESat begins to take its measurements, the Ohio State
team will help calibrate GLAS. Csathos’ laboratory will host
one of the space agency’s remote computing facilities for the
mission, which means the researchers will be responsible for
testing new data processing ideas, and will work closely with
NASA throughout the mission. NASA has assigned several other
research groups around the country to similar tasks, so it can
compare all the results before making mission decisions.

Turning numerical satellite data into high-quality information,
such as geophysical parameters of the surface, isn’t computationally
intensive so much as data intensive, Csatho explained.

"The data comes in from the satellite as photons received
per unit time — that’s it," she said. "So our processing
has to make that data useful to people. That’s what’s exciting
about this project. We start out with points and numbers, then
the data goes through various kinds of processing and we end
up with a wonderful map."

Other Ohio State team members also include David
Bromwich, senior research scientist at BPRC and associate
professor of geography, and Kees van der Veen, research scientist
at BPRC. The two will help process and interpret the ICESat data
as it comes in.

Ohio State is especially suited to contribute to ICESat, van
der Veen said, because of the breadth of expertise and history
of collaboration at BPRC. "We have experts in satellite
processing as well as data interpretation," he said. "Most
facilities only have one or the other, or have little communication
between the two groups."

Van der Veen eagerly awaits the ICESat data. "From my
perspective, the question is, what are the ice sheets doing?
Are they getting bigger or smaller? Once we know that, we can
combine the ICESat data with other data to figure out why changes
are happening, and whether they are part of larger trends. Ultimately,
that’s the Holy Grail of glaciology — to be able to predict
whats going to happen in the future."

Given the public interest in global climate change, the group
plans various outreach activities throughout the mission. Most
recently, Ohio State hosted a three-day tutorial followed by
a workshop on laser altimetry for scientists, educators, and
students.

Contact: Bea Csatho, (614) 292-6641; Csatho.1@osu.edu.

Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu.