GRACE Gravity Model 02

The GRACE Gravity Model 02 (GGM02) has been released to the public. This global Earth gravity model is a significant improvement upon, and supersedes, the previously released model GGM01.

The GGM02 model is based on the analysis of 363 days of GRACE in-flight data, spread between April 4, 2002 and Dec 31, 2003. As before, this model is available in two forms: GGM02S - complete to harmonic degree 160 - is derived purely from GRACE satellite data, and is unconstrained by any other information; and GGM02C - complete to degree 200 - is constrained with terrestrial gravity information.

The GGM02 model is released with the following information:

• GGM02 - An improved Earth gravity field model from GRACE (6.4 MB - PDF)
• GGM02 Notes (PDF)
• GGM02 Model Archive (ZIP) - Download Stuffit Expander

The GGM02 models should be cited as: Tapley, B., J. Ries, S. Bettadpur, D. Chambers, M. Cheng, F. Condi, B. Gunter, Z. Kang, P.Nagel, R. Pastor, T. Pekker, S.Poole, F. Wang, "GGM02 - An improved Earth gravity field model from GRACE", Journal of Geodesy (2005), DOI 10.1007/s00190-005-0480-z The original publication is available at www.springerlink.com

The previously released GGM01 model is now available here.

For more information, please contact the Center for Space Research at 512-471-5573 or e-mail: grace@csr.utexas.edu.

Further Progress in Measuring the Earth's Gravity Field

Prior to GRACE, the long-wavelength part of the Earth's gravity field from space was determined from various tracking measurements of Earth orbiting satellites. These measurements were of considerably varying vintage and quality, and of incomplete geographical coverage. Consequently the accuracy and resolution of the Earth gravity field models were limited, with most of the satellite contributions limited to wavelengths of 700 km or longer. At shorter wavelengths, the errors were too large to be useful. Only broad geophysical features of the Earth's structure could be detected. As a result, improvements to the Earth gravity models at medium & short wavelengths had to come from the use of measurements of terrestrial or marine gravity - also of varying vintage, quality and geographic coverage.

The new GGM02 model builds upon the experience with the older GGM01 model, and is also derived from globally distributed, precise inter-satellite range rate measurements derived by the GRACE mission. This model used improved GRACE mission data and processing methods, when compared to the previously released model. As a result, the GGM02 models are more accurate than the GGM01 models at all wavelengths. In these images, the increased resolution of satellite-determined gravity field can be seen clearly.

Gravity anomalies from decades of tracking Earth-orbiting satellites

Gravity anomalies from 111 days of GRACE data (GGM01S)

Gravity anomalies from 363 days of GRACE data (GGM02S)

A milligal is a convenient unit for describing variations in gravity over the surface of the Earth. 1 milligal (or mGal) = 0.00001 m/s2, which can be compared to the total gravity on the Earth's surface of approximately 9.8 m/s2. Thus, a milligal is about 1 millionth of the standard acceleration on the Earth's surface.

Applications

These gravity field model improvements allow solid Earth scientists to more accurately infer the Earth's internal structure at finer resolution than ever before possible from space. Ocean scientists can combine this gravity model with ocean height measurements from satellite altimeters to study global ocean circulation on a finer scale than has been previously possible. These will, in turn, enable a better understanding of the processes that drive the Earth's dynamic system (solid Earth, ocean and atmosphere), thus leading to better analysis and predictions of climate change & natural hazards

• Solid Earth Science (updated to GGM02)
• Oceanographic Sciences (updated to GGM02)
• Geodesy
• Earth's Gravity Definition (updated)