Auxiliary Space-Based Systems for Interpreting Satellite Altimetry: Satellite Gravity

This chapter outlines satellite altimetry: the mean geoid and the mass component of sea level, or ocean bottom pressure variability and discusses how the mean gravity field is determined from Gravity Recovery and Climate Experiment (GRACE) and Gravity Field and Steady-State Ocean Circulation Explorer. It also discusses how it can be combined with surface gravity from marine and airborne gravity, satellite altimetry, and terrestrial gravity to obtain even higher resolution geoids. The chapter describes how time-variable gravity is estimated from GRACE, how it is converted to mass density, and how the relatively small signal of ocean mass variability is extracted from the noisy measurement. It explores how the mean geoid and altimetry can be combined to determine the mean dynamic topography, from which the surface geostrophic currents can be derived. The chapter discusses how ocean bottom pressure variations are related to sea level measured by an altimeter and to changes in the deep ocean circulation.