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 competencies and with regard for appropriate balance.

This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.

This report and the committee were supported by the National Oceanic and Atmospheric Administration. The views expressed herein are those of the authors and do not necessarily reflect the views of the sponsor.

This study was supported by Contract No. 50-DKNA-6-90040 between the National Academy of Sciences and the National Oceanic and Atmospheric Administration. Any opinions, findings,conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the organizations or agencies that provided support for the project.

Cover art, by Winslow Homer, titled "The Fog Warning." Provided by the Otis Norcross Fund, courtesy of the Museum of Fine Arts, Boston, Massachusetts.

Library of Congress Catalog Card Number 98-84912