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    NATIONAL ACADEMY PRESS 2101 Constitution Avenue, N.W. Washington, DC 20418

    NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

    This study was supported by Contract/Grant No. NAG5-8766 between the National Academy of Sciences and NASA. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project.

    International Standard Book Number 0-309-07401-0

    Cover: Space radar image of the Weddell Sea. The cover image shows two large ocean circulation features, called eddies, at the northernmost edge of the sea ice pack in the Weddell Sea, off Antarctica. The eddy processes in this region play an important role in the circulation of the global ocean and the transportation of heat toward the pole. The image was produced at NASA's Jet Propulsion Laboratory by the Alaska SAR Facility's ScanSAR processor system, using data obtained on October 5, 1994 during the second flight of the Spaceborne Imaging Radar S/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) onboard the space shuttle Endeavour. The image has been reversed for purposes of this cover. In reality, the ocean eddies have a clockwise (or cyclonic) rotation. The dark areas are new ice and the lighter green areas are small sea-ice floes that are swept along by surface currents. First year seasonal ice is shown in the darker green area. The open ocean to the north is uniformly bright and appears blue. The small image inserted on the back cover shows the size of a standard space-borne radar image as a comparison to what can be created when the radar instrument is used in the ScanSAR mode (the main image). This image and many others are available at NASA's Visible Earth website, <>, which provides a central catalog of Earth science-related visualizations and images.

    Additional copies of this report are available from: National Academy Press 2101 Constitution Avenue, N.W. Lockbox 285 Washington, DC 20055 800-624-6242 202-334-3313 (in the Washington metropolitan area)

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    Copyright 2001 by the National Academy of Sciences. All rights reserved.

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