SATELLITE GRAVITY AND THE GEOSPHERE

Contributions to the Study of the Solid Earth and Its Fluid Envelope

Committee on Earth Gravity from Space

U.S. Geodynamics Committee

Board on Earth Sciences and Resources

Commission on Geosciences, Environment, and Resources

National Research Council

National Academy Press
Washington, D.C. 1997



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope SATELLITE GRAVITY AND THE GEOSPHERE Contributions to the Study of the Solid Earth and Its Fluid Envelope Committee on Earth Gravity from Space U.S. Geodynamics Committee Board on Earth Sciences and Resources Commission on Geosciences, Environment, and Resources National Research Council National Academy Press Washington, D.C. 1997

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope 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 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 study was supported by Grant No. NAG 5-3105 between the National Academy of Sciences and the National Aeronautics and Space 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 this project. Library of Congress Catalog Card Number 97–67450 International Standard Book Number 0-309-05792-2 Additional copies of this report are available from: National Academy Press 2101 Constitution Ave., NW Box 285 Washington, DC 20055 800-624-6242 202-334-3313 (in the Washington Metropolitan Area) http://www.nap.edu Cover art by Walter Smith, National Oceanic and Atmospheric Administration. The cover is a color shaded relief image of the Earth's gravity anomaly field. Warm colors (yellow-orange-red) indicate stronger than normal gravity, whereas cool colors (cyan-blue-violet) indicate weaker than normal gravity. Highlights are illuminated from the northwest. The image combines data from EGM96 over land areas with data derived from satellite altimetry (Smith and Sandwell, 1995a) over ocean areas. Copyright 1997 by the National Academy of Sciences. All rights reserved. Printed in the United States of America First Printing, September 1997 Second Printing, March 1998

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope COMMITTEE ON EARTH GRAVITY FROM SPACE JEAN O. DICKEY, Chair, Jet Propulsion Laboratory/California Institute of Technology, Pasadena CHARLES R. BENTLEY, University of Wisconsin, Madison ROGER BILHAM, University of Colorado, Boulder JAMES A. CARTON, University of Maryland, College Park RICHARD J. EANES, University of Texas, Austin THOMAS A. HERRING, Massachusetts Institute of Technology, Cambridge WILLIAM M. KAULA, University of California, Los Angeles GARY S. E. LAGERLOEF, Earth and Space Research, Seattle, Washington STUART ROJSTACZER, Duke University, Durham, North Carolina WALTER H. F. SMITH, NOAA Geosciences Laboratory, Silver Spring, Maryland HUGO M. VAN DEN DOOL, NOAA Climate Prediction Center, Camp Springs, Maryland JOHN M. WAHR, * University of Colorado, Boulder MARIA T. ZUBER, Massachusetts Institute of Technology, Cambridge Staff ANNE M. LINN, Senior Program Officer VERNA J. BOWEN, Administrative Assistant *   Resigned as a committee member on December 1, 1996; served as consultant to the committee through the end of the study. 

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope U.S. GEODYNAMICS COMMITTEE BRADFORD H. HAGER, Chair, Massachusetts Institute of Technology, Cambridge DON L. ANDERSON, California Institute of Technology, Pasadena RICHARD CARLSON, Carnegie Institution of Washington, D.C. THURE CERLING, University of Utah, Salt Lake City RICHARD S. FISKE, Smithsonian Institution, Washington, D.C. GRANT GARVEN, The Johns Hopkins University, Baltimore, Maryland GARY A. GLATZMAIER, Los Alamos National Laboratory, Los Alamos, New Mexico RAYMOND JEANLOZ, University of California, Berkeley KENNETH C. MACDONALD, University of California, Santa Barbara ELIZABETH L. MILLER, Stanford University, California HENRY N. POLLACK, University of Michigan, Ann Arbor MARY LOU C. ZOBACK, U.S. Geological Survey, Menlo Park, California Staff CHARLES MEADE, Senior Program Officer VERNA J. BOWEN, Administrative Assistant

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope BOARD ON EARTH SCIENCES AND RESOURCES J. FREEMAN GILBERT, Chair, University of California, San Diego MARK P. CLOOS, University of Texas, Austin JOEL DARMSTADTER, Resources for the Future, Washington, D.C. KENNETH I. DAUGHERTY, E-Systems, Fairfax, Virginia NORMAN H. FOSTER, Independent Petroleum Geologist, Denver, Colorado CHARLES G. GROAT, University of Texas, El Paso DONALD C. HANEY, University of Kentucky, Lexington RAYMOND JEANLOZ, University of California, Berkeley SUSAN M. KIDWELL, University of Chicago, Illinois SUSAN KIEFFER, Kieffer & Woo, Inc., Palgrave, Ontario PHILIP E. LAMOREAUX, P.E. LaMoreaux and Associates, Inc., Tuscaloosa, Alabama SUSAN M. LANDON, Thomasson Partner Associates, Denver, Colorado J. BERNARD MINSTER, University of California, San Diego ALEXANDRA NAVROTSKY, Princeton University, New Jersey JILL D. PASTERIS, Washington University, St. Louis, Missouri EDWARD C. ROY, JR., Trinity University, San Antonio, Texas EDWARD M. STOLPER, California Institute of Technology, Pasadena MILTON H. WARD, Cyprus Amax Minerals Company, Englewood, California Staff CRAIG M. SCHIFFRIES, Director THOMAS M. USSELMAN, Associate Director WILLIAM E. BENSON, Senior Program Officer ANNE M. LINN, Senior Program Officer CHARLES MEADE, Senior Program Officer LALLY A. ANDERSON, Staff Associate VERNA J. BOWEN, Administrative Assistant JENNIFER T. ESTEP, Administrative Assistant JUDITH L. ESTEP, Administrative Assistant

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES GEORGE M. HORNBERGER, Chair, University of Virginia, Charlottesville PATRICK R. ATKINS, Aluminum Company of America, Pittsburgh, Pennsylvania JAMES P. BRUCE, Canadian Climate Program Board, Ottawa, Ontario WILLIAM L. FISHER, University of Texas, Austin JERRY F. FRANKLIN, University of Washington, Seattle THOMAS E. GRAEDEL, Yale University, New Haven, Connecticut DEBRA KNOPMAN, Progressive Foundation, Washington, D.C. KAI N. LEE, Williams College, Williamstown, Massachusetts PERRY L. McCARTY, Stanford University, California JUDITH E. McDOWELL, Woods Hole Oceanographic Institution, Massachusetts RICHARD A. MESERVE, Covington & Burling, Washington, D.C. S. GEORGE PHILANDER, Princeton University, New Jersey RAYMOND A. PRICE, Queen's University at Kingston, Ontario THOMAS C. SCHELLING, University of Maryland, College Park ELLEN SILBERGELD, University of Maryland Medical School, Baltimore VICTORIA J. TSCHINKEL, Landers and Parsons, Tallahassee, Florida E-AN ZEN, University of Maryland, College Park Staff STEPHEN RATTIEN, Executive Director GREGORY SYMMES, Assistant Executive Director JEANETTE SPOON, Administrative Officer SANDI FITZPATRICK, Administrative Associate MARQUITA SMITH, Administrative Assistant/Technology Analyst

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council.

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope This page in the original is blank.

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope Preface For the past three decades, it has been possible to measure the Earth's static gravity field from satellites. Such measurements have been used to address many important scientific problems, including the internal structure of the Earth and geologically slow processes such as mantle convection. In recent years, improved accuracy of satellite gravity measurements has made it possible to resolve the time-varying component of the global gravity field. These temporal variations are caused by dynamic processes that change the mass distribution in the Earth, oceans, and atmosphere, and could potentially be used to study a new class of important scientific problems. The Committee on Earth Gravity from Space was formed under the auspices of the National Research Council's U.S. Geodynamics Committee to undertake the following tasks: evaluate the potential for using satellite technologies to measure the time-varying component of the gravity field; assess the utility of an improved global gravity field in general, and the time-varying component in particular, for addressing problems of interest to the earth science, natural hazards, and resource communities; and determine what complementary data are needed to increase the usefulness of satellite-derived gravity data. With regard to the first charge, the committee reviewed approximately a dozen mission concepts that were planned or envisioned by investigators in the United States and Europe. We grouped the missions into broad categories and developed a "generic" mission scenario for each category. In the course of our investigation it became clear that future technological refinements might yield more information than is currently feasible, so we expanded our list of generic mission scenarios to include future possibilities as well as current ones. We investigated the trade-offs in orbit design that affect the spatial and temporal resolution of the mission, and chose the altitudes for our generic missions. Mission resolutions were estimated assuming a white-noise error source in the measurements and an isotropic distribution of errors over the Earth. These assumptions simplified the committee's work and left the results generic and not tied to a specific mission proposal. The white noise levels we chose were calibrated initially so that the results corresponded closely with more detailed mission simulations in the published literature (reviewed in Chapter 2). We then adjusted the noise levels to reflect what we thought was currently feasible or likely from future technology,

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope and asked the scientists and engineers involved in the design of current missions to review our estimates. Based on that review, we made some refinements in the white noise levels and added recommendations about ancillary acceleration and tracking data. We believe that this process has yielded results that are sufficiently generic to be broadly useful, but that also accurately reflect the capability of current technology. The committee addressed its second and third charges by focusing on two classes of scientific problems: (1) fields of study that would be significantly advanced by a dedicated satellite gravity mission, and (2) fields that would benefit from improved gravity data but that would also require ancillary data to interpret the results. The committee also considered phenomena that move mass, but that are not currently amenable to study with satellite gravity data because of small size, high speed, or difficulty in isolating the relevant geophysical signal. A large number of natural hazards fall into this category. With a few exceptions, these phenomena are not discussed in this report Because relatively little has been written on the application of the time-varying component of the gravity field to scientific problems, it was necessary for the committee to conduct a substantial amount of original research and to develop forward models. I would like to extend my appreciation to the committee, which undertook the demands of this study with collegial enthusiasm and a remarkable ability to work across disciplines. Each member made an important and unique contribution to the report Special thanks go to Richard Eanes, who had the time-consuming and difficult task of generalizing a dozen proposed or envisioned gravity missions into generic mission classes, and John Wahr, who modeled (and remodeled) all the time-varying phenomena discussed in this report. Although John had to leave the committee in December 1996 to honor a previous commitment, he continued, as a consultant, to complete the final model runs on behalf of the committee. The committee also expresses it sincere appreciation to the staff of the Board on Earth Sciences and Resources, and particularly to Anne Linn, Study Director of this project, for a job superbly done. Finally, I would like to thank the individuals who made presentations to the committee or who provided input to the study. They include Knut Aagaard, Peter Bender, Srinivas Bettadpur, Bruce Bills, David Bromwich, Frank Bryan, William F. Budd, Steve Castles, Ben Chao, T.C. Chen, Tom Clark, Oscar Colombo, Ab Davis, Mike DiPirro, Danon Dong, Mario B. Giovinetto, Arnold Gordon, Brad Hager, Gordon Hamilton, K.H. Ilk, Yu Jin, Masao Kanamitsu, Günther Können, Steve Marcus, Marcia McNutt, Mark Meier, Bill Melbourne, P.C.D. Milly, Mery Molenaar, RS. Nerem, Lauri Newman, Denis O'Brien, Ho Jung Paik, Erricos Pavlis, Dick Rapp, Mark Richards, Rick Rosen, Suranjana Saha, Jae Schemm, Peter Shirron, Dave Smith, Detlef Stammer, Court Stevenson, Byron Tapley, Jim Titus, Kevin Trenberth, Michael Watkins, Raymond Willemann, and Victor Zlotnicki. Jean O. Duckey Chair

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope Contents     EXECUTIVE SUMMARY   1     Benefits of a Dedicated Satellite Gravity Mission,   2     Mission Scenarios and Measurement Techniques,   2     Ocean Dynamics and Heat Flux,   3     Solid Earth Processes,   4     Water Cycling,   4     Sea-Level Rise and Glaciology,   4     The Dynamic Atmosphere,   5     A Tool for Science,   5 1   INTRODUCTION   7     Scientific Overview,   7     The Atmosphere as a Potential Source of Noise for Time-Dependent Applications,   10     History of Satellite Gravity,   11     ''Gravity" as Used in this Report,   13     Organization of Report,   14 2   MISSION SCENARIOS AND MEASUREMENT TECHNIQUES   15     Satellite Observations of the Gravity Field,   16     Trade-offs in Spacecraft Mission Design,   16     Mission Scenarios,   19     GPS,   19     SST and SSI,   19     SGG and SGGE,   20     Previous Studies,   20     Error Estimates for Mission Scenarios of this Report,   21     Degree Amplitude Error Spectra,   21     Precision Versus Resolution,   23     Standard Generic Missions,   27     Conclusions,   27

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope   3   THE GRAVITY FIELD AS A TOOL FOR SCIENCE   29     Reference Frame (1): The Foundation for Measuring the Changing Earth,   29     Reference Frame (2): The Geoid, Fluid Circulation, and Satellite Altimetry,   30     Data Calibration and Verification: Giving Old Data New Value,   31     Conclusions,   33 4   OCEAN DYNAMICS AND HEAT FLUX   35     Static Field,   35     Time-Dependent Measurements,   40     Bottom Pressure and Mass,   41     Steric Changes,   43     Accuracy,   44     Conclusions,   45 5   SOLID EARTH PROCESSES   47     Mantle Convection and Plumes: Understanding the Earth's Heat Engine,   47     Post-Glacial Rebound,   49     Regional Deformation and Structure: The Surface Manifestation of Plate Tectonics,   55     Earthquakes,   58     Conclusions,   58 6   WATER CYCLING   59     Water Transfer to the Atmosphere,   59     Soil Moisture Inventory,   63     Gravity and the GEWEX Continental-Scale International Project,   63     Snowload and Associated Runoff,   64     Aquifers,   64     Conclusions,   64 7   SEA-LEVEL CHANGE   67     Thermal Expansion of the Oceans,   67     Ice Mass Balance,   71     Contributions from the Greenland and Antarctic Ice Sheets,   71     Contributions from Glaciers,   76     Conclusions,   77 8   THE DYNAMIC ATMOSPHERE: UNRAVELING THE CONTRIBUTIONS OF THE EARTH'S SUBSYSTEMS   79     Conclusions,   86 9   CONCLUSIONS   87     AFTERWORD   89     APPENDIXES     A Spherical Harmonics: Degree Variances, Wavelengths, Upward Continuation, Anomalous Potentials, Signal and Error Spectra, and Gaussian Averages   91     B Modeling   99     ACRONYMS   105     REFERENCES   107

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope Satellite Gravity and the Geosphere Contributions to the Study of the Solid Earth and Its Fluid Envelope

OCR for page R1
Satellite Gravity and the Geosphere: Contributions to the Study of the Solid Earth and its Fluid Envelope This page in the original is blank.