**3. GRACE data products**

The three official processing centers forming the GRACE Science Data Center (GSDC), i.e. the Center for Space Research (CSR) in Austin, Texas, United States; the GeoFoschungsZentrum (GFZ) in Potsdam, Germany; the Jet Propulsion Laboratory (JPL) in Pasadena, California, United States, produce the Level-1B parameter products and the Level-2 solutions derived from measurements of the GRACE mission. Level-1B products are constituted by the processed positions and velocities, which were measured by the on-board GPS receivers, accelerometers and the accurate K-band measurements of the variations in distance between the two vehicles. Using these measurements, the monthly gravity field models or Level-2 products for continental hydrology are computed. These products are expressed by means of geoid heights and Equivalent-Water Heights (EWH). The latter products are distributed by the GFZ's Integrated System Data Center (ISDC, [8]), and the JPL's Physical Oceanography Distributive Active Data Center (PODAAC, [9]).
