HEPL Monthly Seminar

Monday 14 February 2005, 4pm
Location HEPL Conference Room

Refreshments at 4pm; Presentation starts at 4:15pm

The GRACE Mission: Status and Science Results

The GRACE mission will accurately map variations in the Earth's gravity field over its 5-year lifetime using two identical spacecraft flying about 220 kilometers apart in a polar orbit 500 kilometers above the Earth. The gravity field is mapped by making accurate measurements of the distance between the two satellites, using GPS and a microwave ranging system. Launched in March 2002, the two GRACE satellites have collected over two years of data. The gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models. The error estimates indicate a 1-cm accuracy uniformly over the land and ocean regions, a consequence of the highly accurate, global and homogenous nature of the GRACE data. Initial results from the GRACE mission also show seasonal variability of the Earth's gravity field at monthly intervals with a 400 km resolution, and a global geoid accuracy of 2-3 mm. These early results are a strong affirmation of the GRACE mission concept.

John Ries is a senior research scientist at the Center for Space Research at The University of Texas at Austin. His research interests include orbit mechanics, geodesy, relativity, and the application of computers and computational techniques to the solution of problems in those areas. He has worked with laser range, altimeter, and Doppler data from satellites such as LAGEOS-1/-2, Starlette, SeaSat, ERS-1/-2, SPOT-2, and TOPEX/POSEIDON. His current efforts are toward improving precision orbit determination for the Jason-1 altimeter mission and gravity model determination for the Gravity Recovery and Climate Experiment (GRACE).

Dr. Ries received his B.S. (1972) and M.S. (1975) in mathematics from Michigan Technological University in Houghton, Michigan. He completed his Ph.D. program in 1989 at The University of Texas at Austin, Department of Aerospace Engineering and Engineering Mechanics. He is a member of the American Geophysical Union, the American Astronomical Society, the AAS Division on Dynamical Astronomy, and a fellow of the International Association of Geodesy.

rev 2/11/05 nc