The GRACE products will be developed, processed and archived in a shared Science Data System (SDS) between the Jet Propulsion Laboratory (JPL), the University of Texas Center for Space Research (UTCSR) and the GeoForschungsZentrum Potsdam (GFZ).
The level-0 to level-2 products are defined as follows (please refer also to above figures):
Level-0:
The level-0 data are the result of the data reception, collection and decommutation by the Raw Data Center (RDC) of the Mission Operation System (MOS) located in Neustrelitz/Germany. The MOS receives twice per day using its Weilheim and Neustrelitz tracking antennae the science instrument and housekeeping data from each GRACE satellite which will be stored in two appropriate files in the level-0 rolling archive at DFD/Neustrelitz. The SDS retrieves these files and extracts and reformats the corresponding instrument and ancillary housekeeping data like GPS navigation solutions, space segment temperatures or thruster firing events. Level-0 products shall be available 24 hours after data reception.
Level-1:
The level-1 data are the preprocessed, time-tagged and normal-pointed instrument data. These are the K-band ranging, accelerometer, star camera and GPS data of both satellites. Additionally the preliminary orbits of both GRACE satellites will be generated. Level-1 data processing software will be developed by JPL with support from GFZ (e.g. accelerometer data preprocessing). Processing of level-1 products will be done primarily at JPL. An identical processing system (hardware/software) will be installed at GFZ to serve as a backup system in case of hardware or network problems. This double implementation is neccessary to guarantee the envisaged level-1 product delay of 5 days. All level-1 products will be archived at JPL's Physical Oceanography Distributed Active Data Center (PODAAC) and at GFZ 's Integrated System Data Center (ISDC) . Both archives will be harmonized on a sub-daily timeframe.
Level-2:
Level-2 data include the short term (30 days) and mean gravity field derived from calibrated and validated GRACE level-1 data products. This level also includes ancillary data sets (temperature and pressure fields, ocean bottom pressure, hydrological data) which are necessary to eliminate time variabilities in gravity field solutions. Additionally the precise orbits of both GRACE satellites will be generated. All level-2 products will be archived at JPL's PODAAC and at GFZ 's ISDC and shall be available 60 days after data taking. The level-2 processing software will be developed independently by all three processing centers using already existing but completely independent software packages which will be upgraded for GRACE specific tasks. Common data file interfaces will guarantee a strong product validation. Routine processing will be done at UTCSR and GFZ, while JPL will only generate level-2 products at times for verification purposes.
The level-2 occultation processing systems at JPL and GFZ are not part
of the GRACE SDS, but both are linked to the SDS archives for retrival
of level-1 products and ancillary ground data and for archiving of their
level-2 products (total electron content, temperature and water vapor).
