The scientific goals of the GRACE mission complements the research focus of a number of international programs, include the World Ocean Circulation Experiment (WOCE), the Climate Variability Program (CLIVAR), and the Global Ocean Observing System (GOOS). These goals are also responsive to the NASA Mission To Planet Earth (MTPE), which has placed a high priority on the need to observe the Earth's gravity field.
The primary goal of the GRACE mission is to obtain accurate global and high-resolution models for both the static and the time variable components of the Earth's gravity field. These gravity field estimates will provide, with unprecedented accuracy, integral constraints on the global mass distribution and its temporal variations. In the oceanographic community,the knowledge of the static geoid, in conjunction with satellite altimeter data, will allow significant advances in the studies of ocean heat flux, long term sea level change, upper oceanic heat content, and the absolute surface geostrophic currents. Further, the estimates of time variations in the gravity field obtained from GRACE, in conjunction with other in-situ data and geophysical models, will help the science community unravel complex processes in oceanography (e.g. deep ocean current changes and sea level rise), hydrology (e.g. large scale evapo-transpiration and soil moisture changes), glaciology (e.g. polar and Greenland ice sheet changes),and the solid Earth sciences. Due to its global coverage and high accuracy, a quantum leap in the accuracy of the models for the Earth's gravity field will be feasible with GRACE.
An additional science goal of the GRACE mission is to enable advances in the atmospheric sciences by the recovery of refractivity (and the derived quantities of temperature and water vapor profiles) and small scale ionospheric structure from the use of GPS radio occultation data.
The Earth's geopotential field will be characterized by the coefficients of a spherical harmonic expansion model. In the baseline science scenario, these coefficients will be estimated to degree and order 160 or more for the long-term mean part, and to degree and order 100 or less for the time variable part. The temporal variability will be characterized by mean values of the coefficients over 30 days or so. In addition, up to 200 GPS atmospheric profile soundings per day will be acquired, subject to data system limitations. These data will provide globally distributed profiles each day of the excess delay, or bending angle of the GPS measurements due to the ionosphere and the atmosphere.