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NASA QuikScat Data Aids Polar Ice, Global Warming Studies
PROVO, Utah-- NASA's newest device to study the ocean's weather patterns not only promises to improve the accuracy of weather forecasts, it may also aid research on shrinking rainforests, melting ice and other factors that influence the earth's long-term health.
Once QuikScat begins transmitting its high resolution radar images back to earth, Brigham Young University engineering professor David Long will use the data to study polar ice over Greenland and Antarctica and to search for evidence of global warming and climatic instability.
"Scatterometer data seems to be particularly well suited for studying polar ice," says Long, a principal investigator on NASA's SeaWinds science team and a former project engineer for the Jet Propulsion Lab (JPL).
"It will provide rapid coverage of the polar regions, at a resolution that allows us to see what's happening on the surface and, in some cases, what's happening below the surface."
In a 1997 report on global warming and polar ice, Long and coauthor Mark Drinkwater of JPL compared scatterometer data from the 1996 NSCAT mission to microwave sensor data from the 1978 SeaSat mission. They found that Greenland's ice sheet showed significant change over those 18 years, that its "melting zone" had moved up, change consistent with a one-degree increase in the earth's temperature.
Since NSCAT was lost to mechanical failure of the spacecraft in 1997, Long has been anticipating new scatterometer data that will help him answer additional questions about the polar ice sheet and global warming.
"The NSCAT data was excellent, high-quality data but unfortunately it didn't monitor a full seasonal cycle. We need to get a whole seasonal cycle of scatterometer data over Antarctica and Greenland, which will help us to understand interannual variabilities, as well as long-term trends," he says.
From its orbit 500 miles above the earth, QuikScat will circle the earth every 100 minutes, sending back high-resolution radar images of 90 percent of the earth's surface every 24 hours. Rather than producing photo images of clouds, the device bounces radar waves off of the earth's surface and provides a measure of "surface roughness."
"What you see in the weather reports are actually satellite photos of clouds. Clouds tell you what's happening in the atmosphere at the level of the cloud formation, but unfortunately that doesn't tell us what's going on at the surface," says Long.
"A radar system can see right through the clouds, to see what's happening on the surface where weather patterns develop. We call the scatterometer an all-weather instrument because it can see through clouds, night and day, and it can see through rain," he says.
When the device is over the water, the scatterometer records tiny centimetric waves called "cat's paws," which are used to calculate wind speed and direction and to track weather patterns. It is designed to detect the earliest signs of weather abnormalities, such as the trade-wind changes along the equator that signal the development of El Nino. NASA has even dubbed QuikScat its "El Nino watcher."
When the scatterometer is over land, it measures surface roughness created by everything from desert sands to forests to ice flows. Rougher surfaces--those with heavy vegetation or glacial ice--reflect a very bright image. In the rainforest, the device images the upper layer of the rainforest canopy.
"Leaves represent extremely rough surfaces, so you get a very bright backscatter from rainforests. The instrument can even detect different sizes of leaves and different species of trees, so we can tell a 'Tarzan of the Apes' kind of jungle from a lighter rainforest or woodland," he says.
Because different types of ice and snow also absorb and reflect the radar in different ways, Long can use scatterometer data to distinguish between dry snow grains, hardened glacial ice and moisture-heavy snowpack. In some cases, tiny ripples on the surface of the snow "dunes" reveal the direction and speed of arctic winds. The researchers can also see where ice melts and refreezes.
A radar image of Antarctica, for example, shows a clear line between the dark, smooth ice cap--which never thaws--and the rougher, brighter "percolation zone"--where snow melts and then refreezes in ice pockets.
"The scatterometer gives us something that no other sensor gives us--we can see different polarizations, different incidence angles--which means we can tell what's underneath the surface of the snow, and that's very important," says Long.
"What we observed in our studies of Greenland was that the line where the snow melts has moved uphill, which indicates some warming and is evidence of change."
Long says stability of the ice pack is a primary concern because polar ice sheets regulate the earth's temperatures.
"Ice sheets are sensitive indicators of climate change. The polar climate system is really the regulator for the entire earth, because it's warm at the equator and cold at the poles and you circulate the heat to keep the poles warm enough and the equator cool enough," he says.
Now that QuikScat has been launched, Long and his students are working with NASA scientists to help calibrate the device and check its reliability. From a ground site in New Mexico, they will record the satellite passes and check the accuracy of the device to make sure it is operating at the correct speed and power.
Student researchers can also take credit for writing some of QuikScat's computer processing code and for creating reference tables that will aid in interpretation of the data.
When he was with the Jet Propulsion Lab, Long was the senior technical designer for NASA's original scatterometer. He has published dozens of papers on applications of scatterometer data and methods to improve data resolution and processing.
The QuikScat instrument was developed, built and managed by JPL for NASA's Office of Mission to Planet Earth, which utilizes technologies designed for space exploration to study the Earth. JPL is a division of the California Institute of Technology in Pasadena, Calif.
Once QuikScat is in orbit and calibrated, the National Oceanic & Atmospheric Administration (NOAA) will assume responsibility for incorporating the data into regular weather reports. -###-
Update: NASA/JPL successfully launched its QuikScat satellite on June 19, 1999. The device will undergo testing and calibration for approximately 30 days, and will then begin providing regular reports for use in weather forecasting. NASA provides updated information on QuikScat, its "El Nino watcher," on its website at: http://winds.jpl.nasa.gov/
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