Recent images produced from the NASA Scatterometer (NSCAT) are giving scientists new insights into the Antarctic ice sheet and the Amazon rainforest after researchers devised ways of using the ocean-monitoring instrument to study land and ice.
The scatterometer's primary function is to study winds over the oceans, but a scientist at Brigham Young University (BYU), Provo, Utah, has come up with a way of enhancing the resolution of the instrument's radar backscatter to take a detailed look at land and ice surfaces as well.
"A radar scatterometer measures the radar backscattering cross-section of the Earth's surface. Measurements of the backscatter over the ocean are used to infer the near-surface wind speed and direction, but can also be used over land to study ice and vegetation," said Dr. David Long, an NSCAT team member at BYU. "Areas which reflect more microwaves are typically rougher and appear brighter in the images than smoother areas which reflect less. The electrical properties of the surface also affect the image brightness. This is the first time we've been able to provide rapid, global coverage that is both uniform and accurate at this resolution."
The polar regions play a central role in regulating global climate, and it is important to accurately record and monitor the extent and surface conditions of the Earth's major ice masses, according to Long. Scientists are using the Antarctic image to understand the effects of the ice pack on the ocean and climate systems. The image shows variations in the ice sheet, as well as a "super-iceberg" that broke off the Thwaites ice tongue and is now circulating in the sea-ice pack.
"Spaceborne radar remote sensors are uniquely well-suited for mapping the polar regions since the radar can image the surface through clouds and both day and night. Similarly, radars are also useful for vegetation studies because different vegetation types and densities have different radar responses," Long said. "Tropical rainforests are critical to the climatic health of the Earth and are thought to contain half of all the world's species."
The new NSCAT image shows the extent of the tropical rainforest. The false color image is being used by scientists to identify types of vegetation on the surface which allows them to differentiate between areas of tropical rainforest and regions of woodlands and savanna.
"This technique of using the scatterometer to study land and ice is a great new application of this radar instrument. We can get measurements of ice extent for use in research and as an aid to shipping and we get them accurately and frequently under all weather conditions," said Jim Graf, the NSCAT Project Manger at JPL. "We can view large-scale vegetation changes enabling us to track the processes of desertification and deforestation. Data from the NSCAT instrument is extremely versatile and can be used to measure short-term changes over the oceans and long-term changes over the land and ice."
The scatterometer uses an array of stick-like antennas that radiate microwave pulses in the Ku-band across broad regions of the Earth's surface. A small fraction of the energy in the radar pulses is reflected back and captured by NSCAT's antennas. At any given time NSCAT's array of six dual beam antennas scans two swaths of ocean or land --one on either side of the satellite's near-polar, sun-synchronous 800-kilometer (500-mile) orbit. Each swath is 600 kilometers (375 miles) wide. The swaths are separated by a gap of about 350 kilometers (215 miles) directly below the satellite, where no data collection is possible.
The scatterometer makes 50-kilometer (30-mile) resolution measurements of the wind over the oceans. This resolution is too coarse for most land and ice studies, but through computer processing of the data, Long is able to produce images with a resolution of 8 kilometers (4.8 miles) or better. "This resolution is still coarse when compared with photographs, but it is nearly ideal for studying many land and ice processes," Long concluded.
The NSCAT instrument was launched August 16, 1996, aboard Japan's Advanced Earth Observing Satellite (ADEOS). ADEOS is an international global change research mission of the National Space Development Agency of Japan (NASDA), which includes instruments from the United States, Japan and France and investigators from many other countries. The satellite is a key part of an international environmental research effort that includes NASA's Mission to Planet Earth (MTPE) program, a long- term, coordinated research effort to study the Earth as a global environmental system. The goal of MTPE is to develop a better scientific understanding of natural environmental changes and to distinguish between natural and human-made changes and impacts.
The Jet Propulsion Laboratory developed, built and manages the NSCAT instrument for NASA's Office of Mission to Planet Earth, Washington, D.C.
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