Small
cylinders dropped from airplanes gather atmospheric data on their way down
Inside a cylinder that is about the size
of a roll of paper towels lives a circuit board filled with sensors. It's
called a dropsonde, or "sonde" for short. It's a work horse of
hurricane forecasting, dropping out of "Hurricane Hunter" airplanes
right into raging storms. As the sonde falls through the air, its sensors
gather data about the atmosphere to help us better understand climate and other
atmospheric conditions.
"Dropsondes have a huge impact on
our understanding of hurricanes and our ability to predict hurricanes,"
explains electrical engineer Terry Hock at the Earth Observing Laboratory in
the National Center for Atmospheric Research (NCAR), located in Boulder, Colo.
With support from the National Science
Foundation (NSF), Hock and his colleagues at NCAR have been designing, building
and improving dropsonde technology for more than 30 years. "Our most
current development is a fully automated dropsonde system for NASA's unmanned
Global Hawk aircraft," says Hock.
Compared to earlier models, today's
sondes are lighter weight, relatively inexpensive and loaded with sensors.
"We have a lot of electronics and,
on the back side, a battery pack to operate the sonde. We have a temperature
and two humidity sensors, and we have a GPS receiver," explains Hock, as
he points out the different circuit board components. "As the sonde moves,
we're using that GPS receiver to track the sonde's movements very precisely,
which is then telling us the wind speed and wind direction. At the top of the
sonde is a parachute which slows down the descent."
Electrical engineer Dean Lauritsen, a
member of Hock's team, developed the system software on the aircraft, which
controls the aircraft data system and process, and also displays dropsonde data
during the sondes free fall to earth. There's such a system on the HIAPER, the
NSF/NCAR Gulfstream V Research Aircraft, which uses sondes for scientific
research, and a similar system used by the U.S. Air Force Reserve Hurricane
Hunters in Biloxi, Miss., and the NOAA Hurricane Hunters in Tampa, Fla. On
board each aircraft are a computer and a rack of electronic equipment to
monitor and receive information from sondes. "The system is capable of
tracking as many as eight dropsondes in the air at the same time. Each one of
them is transmitting data on a separate frequency as it falls." says
Lauritsen.
From the time the sonde leaves the
aircraft, it is checking surroundings two times a second and sending
information back to the aircraft, including pressure, temperature, humidity,
wind speed, and wind direction. Future developments are expected to include
sensors for chemicals such as ozone.
"We're taking vertical slices of
the atmosphere constantly as the sonde falls," says Hock. "We're
seeing very precise single measurements show up immediately on the computer
screen."
Researchers process the information
using NCAR-developed custom software, and then send it to weather forecasters
and researchers around the world. In the case of the Hurricane Hunters, the
information goes to the National Hurricane Center in Miami.
NCAR software engineer Charlie Martin
develops custom software called ASPEN, which stands for Atmospheric Sounding
Processing Environment. ASPEN helps make sense of all the dropsonde data.
"Once the dropsonde has fallen through the atmosphere and the data has
come back to the aircraft, that raw data needs a little more treatment before
we send it to weather services around the world," explains Martin.
Martin points to a map showing a
compilation of dropsonde wind data collected in August 2011, as Hurricane Irene
was churning its way toward the Florida coast. "The winds are in a
circular pattern," says Martin, as he identifies small triangles on the
map that represent the wind and wind direction. "The center of the
hurricane is clearly depicted in the center of the circular pattern. The
National Hurricane Center uses this data along with other data to classify the
hurricane and assign a category to it."
Hock and his team also custom fit
aircraft with launchers to deploy the sondes, including one system for
helium-filled balloons. In 2010, American and French researchers deployed
balloons over Antarctica that dropped 600 sondes over a four-month period to
study atmospheric conditions and the shifting ozone layer. "There is now a
very dense set of measurements that came out of this project that has mapped
the Antarctic atmosphere like it has never been done before," notes
Martin.
"Atmospheric conditions above the
Antarctic continent are hard to study since only a handful of sounding stations
are regularly maintained there," says Peter Milne, program manager for
ocean and atmospheric sciences within NSF's Office of Polar Programs. "Fortunately,
the Antarctic polar vortex, a huge cyclone that sets up above the entire
continent, is like the NASCAR of long distance ballooning, with balloons
sweeping around the continent for as long as they stay aloft. Using these
drifting platforms provided a unique data set."
Such "inside information" is
helping scientists learn more about climate and hurricanes. Data from
dropsondes is also giving scientists a better understanding about atmospheric
conditions that spawn any number of weather conditions. Hock expects this will
help forecasters make earlier and more precise hurricane predictions, giving
people in the path of a killer storm more time to get out of harm's way.
Miles O'Brien, Science Nation
Correspondent
Ann Kellan, Science Nation Producer
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