The GRACE twin satellites, launched 17 March 2002, are making detailed measurements of Earth's gravity field and are revolutionizing investigations about Earth's water reservoirs, large-scale solid earth changes, ice cover, and oceans. To aid in the interpretation of gravity change over the oceans, the GRACE Tellus project provides ocean bottom pressure (OBP) derived from the GRACE satellites. OBP is the sum of the mass of the atmosphere and ocean in a 'cylinder' above the seafloor.