Byron D. Tapley

2001 Charles A. Whitten Medal Winner

Byron D. Tapley received the Charles A. Whitten Medal at the 2001 Fall Meeting Honors Ceremony on 12 December in San Francisco, California. The medal recognizes outstanding achievements in research on the form and dynamics of the Earth and planets.


“The Charles A. Whitten Medal ‘recognizes outstanding achievements in research on the form and dynamics of the Earth and planets.’ Professor Byron Tapley is truly deserving of this prestigious award.

“For more than four decades, Byron Tapley has been an educator, a researcher, and a visionary who has made unique and significant contributions to advancing the field of space geodesy into an interdisciplinary branch of Earth and planetary science. The evolution of the field called geodesy, defined in the nineteenth century as the science ‘that measures size and shape of the Earth,’ into the discipline that now also ‘measures the changes of the size and shape of the Earth and the planets,’ is owed to a few pioneers who have been developing geodesy into what it is today. Byron Tapley is among the elites who have pioneered this interdisciplinary science in space geodesy, which is now routinely associated with contemporary problems in geodynamics, geophysics, oceanography, and climate change.

“He is cited for his innovative applications of statistical orbit determination and satellite dynamics theory to pioneer and advance the discipline of modern satellite geodesy for interdisciplinary Earth science. Here I will highlight only a few of his many scientific accomplishments.

“Byron Tapley’s early significant contribution, in the 1970s, was his elegant statistical formulation of the nonlinear precision orbit determination and geodetic parameter recovery problem to exploit increasing accurate data collected by planet-orbiting artificial satellites, which began to be available since the advent of the space age. This pioneer work helped create science and application areas such as Earth and lunar mission orbit determination, navigation, positioning and time transfer, reference frame realization, and geophysical and geodetic parameter recovery such as Earth rotation, gravity fields, tides, etc. A recent example is the application of this technique for accurately measuring the position of the TOPEX/POSEIDON satellite, 1300 km above the Earth, to 1-2 cm radially.

“This one-part-per-billion measurement enables the applications of the inferred sea surface height from satellite altimetry for scientific studies, including the now-routine monitoring of El Niño and La Niña phenomena and the study of general ocean circulation and global sea-level change.

“During the 1980s, the development of precise satellite laser ranging (SLR) systems enabled a number of interdisciplinary sciences to be studied with highly accurate measurements for the first time. They include the determination of tidal deceleration of the Moon, absolute tectonic plate velocities, crustal deformations, the measurement of secular change of the Earth’s zonal harmonics (i.e., ‘the Earth getting rounder due to ice melt which started since the last ice age 18,000 years ago’), and its constraint to Earth’s mantle viscosity and Earth’s meltwater budget.

“Even in the presence of the current GPS global network with ever-increasing use of GPS stations, SLR remains a critical and necessary technique for its sensitivity to the geocenter and its contribution to realization of the global terrestrial reference frame.

“Byron Tapley has contributed to the initial establishment of the first global SLR network in support of NASA’s Crustal Dynamics Project. Byron Tapley is among the group who first published the observed J2-dot from SLR to Lageos and the use of the observation to constrain the planet mantle viscosity.

“During the 1990s, in addition to the contribution as the leader of the TOPEX/POSEIDON Precision Orbit Determination Team, Byron Tapley contributed to the contemporary determination of Earth’s gravity field model, especially for the theory and applications of satellite data. The resulting gravity field model solution was used to compute precise orbits of TOPEX/POSEIDON, and the methodologies developed have benefitted subsequent gravity model developments, for example, EGM-96 and TEG-4; and will influence future model developments.

“During the late 1990s, Byron Tapley as the Principal Investigator provided leadership to enable the approval of the first-ever gravity mapping mission, the U.S.-German GRACE mission, which will be flown in 2002. GRACE will provide revolutionary measurements from space for mass motions at the surface or subsurface with an anticipated accuracy of less than 1 cm of fluid movement. These measurements manifest in the form of time-varying gravity field and is contributed by the complex solid Earth-ocean-atmosphere-hydrosphere-cryosphere processes within the Earth system. It has been widely accepted that many of these signals are climate change-sensitive and are critical for studying global climate change.

“Byron Tapley’s contribution to the interdisciplinary field of satellite geodesy is diverse. He is among the elites who have brought this branch of science to be one of the foci of contemporary problems in geophysics. It is my pleasure to have known Byron for over 25 years as a former student and colleague and to be able to describe some of his many accomplishments for which he is awarded the Whitten Medal from the American Geophysical Union.”

—C. K. SHUM, Ohio State University, Columbus


“Thank you C. K. for your generous remarks.

“I am especially pleased to receive this award, not just because of its Union significance, but also because of my previous contact with the individual for which it is named. The broad vision and keen insight possessed by Charles Whitten, along with the enormous contributions that he made to our field, add a special significance to the award.

“I have been very lucky to participate in the exciting transition in geodesy, which has occurred during the past few decades. During this period, geodesy has moved from a predominately regional observation-based science, focused on stationary phenomena, to a science whose framework is global and one in which the temporal changes have become as important as the mean properties. The development of space geodetic techniques allows accurate global measurements with comparatively short campaigns and provides the capability to repeat these measurements as needed. These techniques have transformed geodesy from an essentially observational science to one in which the interpretative phase, in an interdisciplinary context, is of equal importance. To participate in this transformation has been a pleasure and a privilege.

“In accepting this award, it is important to recognize that it is symbolic of the contributions of numerous colleagues and very bright students with whom I have interacted. I have had the good fortune to learn a great deal from both and for this I am very grateful.

“My commitment to the space geodesy field began one morning in the summer of 1977 with a telephone call from George Born, who at that time was at JPL and was responsible for the orbits for the planned SeaSat mission. The mission had a radial orbit accuracy requirement of ten centimeters and the best orbit accuracy achievable at that time was between two and five meters, mostly limited by knowledge of the Earth’s gravity field. George was seeking a lead for an experiment team to implement the first space-based GPS receiver, as a means of obtaining some portion of the two-order magnitude improvement in orbit accuracy that was needed to support the altimeter measurements. This sounded like an interesting extension to my concern with the satellite orbit determination problem and I agreed to the assignment. This decision set a course that is still ongoing and has influenced the efforts of numerous associates and students. The GPS receiver development was troubled and eventually was dropped from the SeaSat instrument complement, only to resurface for all following satellite altimeter missions. I moved on to the lead of the POD/Altimeter Team, where a mixture of radio and optical measurement systems were involved. Although SeaSat lasted only ninety days, the potential for satellite altimeters was demonstrated and the requirement for the following altimeter missions, with the improved tracking and POD approaches and better gravity models, was set. These requirements became major drivers of the space geodesy community during the subsequent decades. The MOBLAS SLR systems, which were base lined as one of the primary systems for tracking SeaSat, were not deployed prior to the satellite failure, but they became the tracking backbone for the altimeter missions during the following decades and for supporting the measurement goals of NASA’s Crustal Dynamics Project.

“The combination of Doppler and SLR tracking along within an extensive community effort to improve the gravity and surface force models provided the basis for the two order magnitude orbit accuracy improvement achieved for the TOPEX/POSEIDON mission. The success in attacking the numerous problems related to meeting the challenging requirements for precise point positioning, whether a satellite in orbit or a point on the Earth’s surface, has been achieved through the contributions of a number of collaborators.

“In the interest of time, I would limit specific recognition to those individuals with whom I have had more or less daily contact. In addition to George Born, these include Bob Schutz, John Ries, C. K. Shum, Mike Watkins, Srinivas Bettadpur, and Richard Eanes. They have been an essential part of the overall effort and share in the success achieved.

“On a personal basis, I would like to recognize the importance of my family. My wife Sophia and our sons Mark and Craig are able to be here tonight. Throughout this period, Sophia has been a valued companion and a point of stability in an otherwise dynamic and sometimes stressful environment. She has endured the long hours and let many of her personal pursuits lag to participate in my commitments. The affection, support, and wise council that she has provided have been a very important ingredient in any measure of success that I have achieved. I am especially pleased that she is here tonight. I am also happy that Craig and Mark could be here. As much as Sophia and I were pleased and amazed by them as children, the interaction with them as adults is even more rewarding.

“In closing, I would like to express my appreciation to the Union, and to my colleagues within the Union, for this award. I trust that our future interactions will be as rewarding as those of the past.”

—BYRON D. TAPLEY, University of Texas, Austin