MISSIONS - Who's Who

Overview: The Science Data Team takes the science telemetry, otherwise known as raw data, received from the TOPEX/Poseidon satellite and turns it into science data products. The science data products are sent to JPL's Physical Oceanography Distributed Active Archive Center (PODAAC) and to NOAA . From these locations, the products are distributed widely over the internet and are turned into various sea surface height, wind speed, significant wave height and atmospheric water vapor products. The products are used by research scientists, educators, and service providers. Service providers use the data to support marine operations such as ship routing. There are a large number of practical applications for the data.

The details: The creation of the science products by the Science Data Team is called the "build process," because there are several steps involved, each adding more information to the data files to refine the observations. Each morning a member of the Science Data Team who works with the Flight Control Team begins processing raw TOPEX/Poseidon data. This analyst, known as the Flight Control Team Data Analyst (FCT DA) or real-time analyst, merges and archives all flight telemetry data and produces two products, Spacecraft Telemetry Records (STRs) which consists of engineering data, and raw instrument data products which contain science data. These are forwarded to a Science Data Team Data Analyst, or SDT DA.

The Science Data Team Data Analyst picks up the engineering and science products and creates the first data records that go out to the world. The first products to be created are the NASA altimeter (ALT) and TOPEX/Poseidon Microwave Radiometer (TMR) Science Data Records (SDRs), which are essentially the data files received directly from the satellite with the engineering data removed through software processing. These products are based on early estimates of the satellite orbit called medium-accuracy orbit ephemeris (MOE) data, which the Science Data Team receives three to four days after the data are received by the FCT DA.

Three to four days later, information from the CNES Sea Surface Meteorology ("Surface Met") file is added to the ALT and TMR SDRs to create what are called Intermediate Geophysical Data Records (IGDRs), which are more comprehensive than the SDRs. About five weeks after this, information received from the Goddard Precision Orbit Determination Team, which provides more accurate orbit ephemeris data, is combined with the IGDRs to create the final NASA science data product the Geophysical Data Records, or GDRs. Once processed, the science products are "packaged," distributed, and archived. Distribution and archiving are handled by two organizations: the Science Data Team Library and JPL's Physical Oceanography Distributed Active Archive Center (PODAAC). From these sources, the data are available to scientists and researchers around the world.

Because the French have their own instruments on board the satellite and process their own data, they only need to receive the raw data from the French altimeter and the DORIS tracking receiver. Raw data are also provided to two other organizations: NASA's Wallops Flight Facility (which developed the NASA altimeter) and the Global Positioning System (GPS) instrument group at JPL. NASA and CNES exchange all final data products, so that each has a complete record of the satellite's observations. At JPL, the NASA and CNES GDRs are merged by PODAAC to produce the final mission data products, called the Merged Geophysical Data Records, or MGDRs.

PODAAC also provides "Quick-Look" data on its Web site at: http://podaac.jpl.nasa.gov/topex/www. Here, the science community and the general public can see colorful maps produced using the IGDRs from the latest 8 hours, 24 hours, 3 days, and 10 days. Maps are presented for three different measurements derived from the data: significant wave height, water vapor content of the atmosphere (as measured by the TOPEX/Poseidon radiometer), and wind speed at the ocean surface. Scientists use the Quick-Look data to get a preview of phenomena they may wish to study more closely when the final GDRs are generated. In addition to the products provided by the TOPEX/Poseidon mission, other organizations make data and information products for specialized use by scientists and people involved in activities such as fisheries management, cable laying, the hydrocarbon industry and marine navigation. See the section on applications at http://topex-www.jpl.nasa.gov/.