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GRACE Gravity Model 03 - Released 2008

The GRACE Gravity Model 03 (GGM03) has been released to the public. This global Earth gravity model is a significant improvement upon, and supersedes, the previously released models GGM01 and GGM02.

The GGM03 model is based on the analysis of four years of GRACE in-flight data, spread between January 2003 and December 2006. As before, this model is available in two forms: GGM03S - complete to harmonic degree 180 - is derived purely from GRACE satellite data, and is unconstrained by any other information; and GGM03C - complete to degree 360 - is combined with terrestrial (ocean and land) gravity information.

The GGM03 model is released with the following information available here:

The GGM03 models should be cited as: B. Tapley, J. Ries, S. Bettadpur, D. Chambers, M. Cheng, F. Condi, S. Poole, The GGM03 Mean Earth Gravity Model from GRACE, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract G42A-03, 2007.

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 GGM03 model builds upon the experience with the older GGM01 and GGM02 models. It is derived from globally distributed, precise inter-satellite range rate measurements derived by the GRACE mission, but it also includes terrestrial gravity information to extend the resolution to degree and order 360. In the following images, the ever-increasing resolution of the satellite-determined gravity field can be seen clearly.

Gravity anomalies from decades of tracking Earth-orbiting satellites
Gravity anomalies from decades of tracking Earth-orbiting satellites

Gravity anomalies from 111 days of GRACE data (GGM01S)
Gravity anomalies from 111 days of GRACE data (GGM01S)

Gravity anomalies from 363 days of GRACE data (GGM02S)
Gravity anomalies from 363 days of GRACE data (GGM02S)

Gravity anomalies from four years (2003-2006) of GRACE data (GGM03S)
Gravity anomalies from four years (2003-2006) of GRACE data (GGM03S)

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

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