Satellite Remote Sensing: The Last Frontier
Scientists gear up to study the Earth's polar regions from space.
By Anthony P. Montesano

Santa Claus aside, the frigid, barren terrain of the Earth's polar regions has historically tested the very limits of human endurance, as explorers sought to discover all they could about the North and South Poles. The unfriendly environments of the Arctic and Antarctic have made first-hand study of these regions hazardous and, consequently, incomplete.
      Now, satellite technology-integrated with advanced data storage and supercomputing systems-offers the scientific community perhaps the best opportunity yet to understand these once-uncharted territories. In early November 1995, the United States and Canada jointly launched RADARSAT, the newest Earth observation satellite equipped with synthetic aperture radar (SAR).
     The RADARSAT project was originally conceived by Canadian industry in cooperation with federal and provincial governments to study Canada's high-latitude regions, i.e., areas bordering the polar icecaps. RADARSAT has a polar orbit of 98.6 degrees, (that is extending to LAT 81.4 degrees N and S), which means that the data it gathers will be of interest not just to Canadian and U.S. scientists but to researchers from around the world interested in the polar regions.
      The SAR capabilities of the satellite will allow acquisition of accurate images, day or night, through clouds, rain and snow-crucial when documenting changes in the Arctic and Antarctic regions. The five year mission of the Canadian-owned satellite is to acquire and downlink geophysical data from the Earth's surface, with emphasis on the polar regions. The raw data will be processed at one location in Canada and one in the U.S. - the NASA-sponsored Alaska SAR Facility, housed in the Geophysical Institute at the University of Alaska Fairbanks.
      ASF, one of nine data centers which comprise NASA's Earth Observing System Data and Information System (EOSDIS), will downlink and process RADARSAT data for the U.S., for distribution primarily to users in the research community.
      One of RADARSAT's primary objectives is to analyze the effect of global warming in the polar regions starting with the first available data in September 1996. According to Craig Lingle, a NASA principal investigator for glaciers in Alaska, RADARSAT will provide scientists studying the polar regions with several advantages over ERS-1, ERS-2 and JERS-1 SAR imagery. Among these advances are RADARSAT's broad beam (500 vs. 100 kilometers) data gathering capabilities; its ability to gather data at varying incidence angles; and its fine beam resolution-listed at 10 meters. Lingle says scientists will use the new tools provided by RADARSAT to 1) assess the role of polar sea ice in the climate system, 2)monitor the response of glaciers to warming trends in the climate and, 3) study their probable contribution to rising sea levels.
      As a result of its broad beam of coverage, RADARSAT will be able to scan the entire Artic region on a weekly basis with a series of 500 x 500-km images that can be captured in 80 seconds. RADARSAT has a variety of beams and modes to choose from. The fine mode offers an image 50 x 50-km in size with approximately 10-meter resolution, while ScanSAR can cover a 500 x 500-km area with about 100-meter resolution. RADARSAT also has a downlink transfer rate of 85 to 105 megabytes per second.
      "The rate and volume of data that we will be dealing with is mind-boggling," said Carl A. Wales, project director at ASF. "RADARSAT can collect up to 28 minutes of radar data per orbit and makes more than 14 orbits a day." That comes to approximately 2793 minutes of radar data a week and over 726,180 minutes of information for the entire mission. The U.S., in return for launching the spacecraft, will receive 10-20 percent of this data.
      As part of this technology exchange agreement, the CSA will rotate the entire satellite for a period of 21 days starting in October 1996. This difficult maneuver will allow RADARSAT to "look" southward and image all of Antarctica, including the South Pole region. The Byrd Polar Research Center at Ohio State University, along with Vexcel, in Boulder, Colorado, are developing a data processing system to convert the image data into a final map product. When concluded, scientists will have nearly 100 CD-ROMs of seamless, terrain corrected image mosaics covering a different quadrant of the continent.
      Lingle says the RADARSAT Antarctica Mapping Project will provide the first complete map of the region. "In the past," he said, "maps have been made using extrapolation of sparse data." Obtaining this complete picture of the ice sheet will be a substantial step forward in assessing the role of the Antarctic ice shet in present and probable future sea-level rise, according to Lingle.
      One of the challenges faced by ASF was how to handle the enormous amount of data collected by RADARSAT. "To store information from RADARSAT, we needed a system that could time code and manage high data rates," said Wales. "After examining several different systems, we chose to work with Sony Electronics' DR-1000 series because it is a cassette-based system with high data transfer rates, time code capability and high storage capacity."
      RADARSAT stores data backscattered from the Earth's surface using onboard tape recorders or real-time links. The data are then downloaded to the ground station in Fairbanks (in the case of U.S. data), where six Sony DR-1000 tape drives are used to record the data. Sony DFC interfaces are also being used in this project, providing both serial and parallel inputs, IRIG A and B record/playback and up to 100 gigabytes of storage capacity per cassette.
      In addition, the Series utilizes sophisticated, built-in diagnosis for detecting operational and system fault conditions in real time. The DIR-1000 also delivers a data transfer rate of up to 32 megabytes per second. "A lot of important information is headed our way," said Wales. "It's nice to know that we have the reliability of the Sony DIR-1000 to store, process, retrieve, and manage all of it properly."
      "There has never been a more important time for us to study the polar regions and their effects on the rest of the planet," said Wales. "As a global community, we are the most ecologically aware we've ever been. Evaluating where to go from here has never garnered more interest from both the scientific community and governments around the globe. RADARSAT and its data stream will probably make a significant contribution to research into global change."

About the Author:
Anthony P. Montesano is a writer specializing in the high-tech, communications and entertainment industries. He may be reached at 212-696-2000.

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