NASA's Earth Observation System Data Information System

by Kevin Schaefer

Over the years, NASA has collected a great deal of Earth science data from dozens of orbiting satellites. With time, these data collections have scattered among many archives that vary significantly in sophistication and access. NASA risked losing valuable, irreplaceable data as people retired, storage media decayed, formats changed and collections dispersed. Scientists began to spend more time searching for data than performing research.

Today, NASA's Office of Mission to Planet Earth, which leads the agency's Earth science research, continues to collect data. This office operates 11 active satellites and instruments, which together produce 450 gigabytes (Gb) of data each day. Landsat alone, one of NASA's most popular sources of remote sensing data, produces 200 Gb of raw data per day. In 1997, NASA will launch the first of many Earth Observation Systems (EOS) satellites and instruments that will double the daily production of raw data. EOS will produce 15 years of global, comprehensive environmental remote sensing data.

To handle the size and variety of data now available and to promote cross-discipline research, NASA created EOSDIS, which drastically reduces the time spent searching for relevant data, allowing scientists to focus their research efforts on changes in the Earth's environment. EOSDIS allows scientists to search many data centers and disciplines quickly and easily, quickening the pace of research. The faster the research, the more quickly scientists can identify causes of detrimental environmental effects, opening the way for policy- and lawmakers to act at international, national and local levels.

The well-known hole in the ozone layer above the Antarctic illustrates the process from research to policy to law. Researchers first discovered the ozone hole when lofting a weather balloon from an Antarctic research station. But NASA's NIMBUS 7 satellite had the necessary instruments, so why hadn't it detected the hole? Scientists quickly discovered that the calibration algorithm routinely dropped low ozone values as "noise." When they retrieved 12 years of original NIMBUS 7 data, scientists verified the existence of the hole and indicated that it had grown over the last decade. Data from additional instruments revealed that CloroFloroCarbons (CFCs), such as Freon, destroyed the ozone layer and created the hole. Armed with this knowledge, the United States signed several international treaties restricting the production of CFCs. Congress passed regulations on the production, distribution and recovery of CFCs in the United States. As a direct result, worldwide production of CFCs has plummeted. Today, consumers cannot openly buy Freon. Given time, the CFCs already in the atmosphere will disperse and the ozone layer will heal itself.

Another example of the benefits of multiple-discipline Earth science research lies in the work of the EOSDIS Pathfinder projects, which recycle old data from past and current satellites into new products for scientific research. One project used old Landsat data to assess deforestation in the Amazon basin, indicating that the true rate of deforestation closely matches that cited by the Brazilian government, thus ending a long standing, international debate. Now that scientists have settled the extent of deforestation, policy- and lawmakers can act to fix it.

In yet another result of the EOSDIS philosophy, ocean dynamists recently discovered a huge, low-amplitude wave that propagates back and forth across the Pacific Ocean. Only a few inches high, but a thousand miles long, the wave bounces back and forth between South America and Asia. The same scientists also found that sea level has risen slightly over the last few years, while other researchers detected a slight decline in total ice coverage. Are these three phenomena related? If so, why? Only collaborative research between atmospheric physics, ocean dynamics, meteorology and climatology can answer these questions.

The same principles apply to regional and local, as well as national and international, policy and law. Through EOSDIS, state and local governments can obtain accurate data and information about water tables, flood plains, ground cover and air quality. For example, the state of Ohio has begun using NASA remote sensing data to monitor reclamation of strip mining sites, a task for which the state does not have enough personnel to perform on-site inspections.

EOSDIS does a lot more than just store and distribute Earth science data. It also provides the operational ground infrastructure for all satellites and instruments within the Mission to Planet Earth office at NASA. It contains Earth science data from EOS satellites, other MTPE satellites, joint programs with international partners and other agencies, field studies and past satellites. It receives and processes the raw data from the satellites. After initial processing, EOSDIS delivers the data to the Distributed Active Archive Centers (DAACs) for further processing, storage and distribution. EOSDIS also includes mission operations and satellite control.

Distributed Active Archive Centers

The DAACs serve as the interface between EOSDIS and the user community. Each DAAC concentrates on a specific discipline of global change and Earth science, storing all raw satellite data received from the Data Production Facility and processing the raw data into usable products. The products are then distributed on a variety of media, such as magnetic tape or CD-ROM. Users query DAAC content through the Internet, viewing low resolution, browse images of the desired data. EOSDIS has nine DAACs:
  1. Alaska Synthetic Aperture Radar (SAR) Facility (ASF), located outside Fairbanks, Alaska, specializes in sea ice and polar processes.
  2. EROS Data Center (EDC), jointly funded with the U.S. Geological Survey, specializes in land processes; it is located in Sioux Falls, South Dakota.
  3. Goddard Space Flight Center (GSFC), Greenbelt, Maryland, specializes in the upper atmosphere, atmospheric dynamics - the global biosphere.
  4. Jet Propulsion Lab (JPL), in Los Angeles, California, specializes in ocean circulation and air-sea interactions.
  5. Langley Research Center (LaRC), located near Norfolk, Virginia, specializes in radiation budget, aerosols and tropospheric chemistry.
  6. Marshall Space Flight Center (MSFC), Huntsville, Alabama, specializes in the Earth's hydrologic cycle.
  7. National Snow and Ice Data Center (NSIDC), at the University of Colorado in Boulder, specializes in the Earth's cryosphere.
  8. Oak Ridge National Lab (ORNL), jointly funded with the Department of Energy in Oak Ridge, Tennessee, specializes in biogeochemical dynamics.
  9. Socioeconomic Data Archive Center (SEDAC) at the University of Michigan in Saginaw, specializes in integrating socioeconomic and environmental data.
The Science Computing Facilities generate the software algorithms that DAACs use to transform raw satellite data into useful products and perform quality control on DAAC products. One or more Science Computing Facilities support each instrument on each satellite.

EOSDIS Core System

The EOSDIS core system consists of the Science Data Processing Segment, the Flight Operations Segment and the Communications and Systems Management Segment.

The Science Data Processing Segment handles all data production, archive and distribution through the Information Management Service, the Planning and Data Processing System, and the Data Archival and Distribution Services. The Information Management Service performs data search, access and retrieval for the EOSDIS. The Planning and Data Processing System processes the raw data into the standard products offered by the EOSDIS. The Data Archival and Distribution Service permanently stores all data received or produced by EOSDIS.

The Flight Operations Segment, consisting of the EOS Operations Center, the Instrument Support Terminals and the Spacecraft Simulator, supports the EOS satellites and instruments. The Operations Center commands and controls the operation of EOS satellites. The Instrument Support Terminals consist of a few generic workstations dedicated to the command and control of specific instruments. Generally, each instrument will have its own Instrument Support Terminal. The Spacecraft Simulator analyzes general satellite information stripped off the main data stream, searching for trends and problems.

The Communications and Systems Management Segment, consisting of the Systems Management Center and the NASA Internal Network, manages schedules and operations among the DAACs and other elements of the EOSDIS. The Systems Management Center manages network loading, data transfer and overall processing to optimize EOSDIS performance. The Internal Network connects all of the permanent archives, transferring data among all of the DAACs and Science Computing Facilities via a dedicated fiber network utilizing the asynchronous transfer mode. The NASA Science Internet (or Internet for short) links the general user to the EOSDIS. The Internet also links EOSDIS to data centers outside NASA.

The EOSDIS Data and Operations System (EDOS), consisting of the Data Interface Facility, the Data Production Facility and the Sustaining Engineering Facility, handles all telemetry to and from the satellite and performs the initial data processing. The Data Interface Facility is the primary communication and data link between the ground and the satellites. The Data Interface Facility separates the main data stream into the scientific and system information. The scientific information goes to the Data Production Facility, while the system information goes to the EOS Operations Control Center and the Spacecraft Simulator. The Data Production Facility separates the scientific data by instruments, calibrates it and attaches any ancillary data (orbit information, for example). All data then gets transferred to the DAACs for permanent storage. The Sustaining Engineering Facility maintains equipment, identifies hardware trends and plans for future upgrades.

The DAACs process the data from each instrument on each satellite into approximately 250 products. Among the many satellite projects from which products are developed are the Tropical Rain Measurement Mission, the Ocean Topography Experiment and Total Ozone Mapping Spectrometer. Through EOSDIS, data products can come from field campaigns, such as the Boreal Ecosystem Atmosphere Study; from satellites operated by other agencies, such as NOAA's Geostationary Orbit Environmental Satellite; and from past NASA missions and programs. Users can locate data products by discipline, DAAC, Earth location, instrument, satellite or time. EOSDIS allows any data format, but uses the Hierarchical Data Format, developed by the National Center for Supercomputing Applications, as the standard.

NASA released Version 0 of the EOSDIS to the general public in 1994. Version 0 connects all the DAACs with some elements of the Science Data Processing Segments, primarily the Information Management Service. Version 0 consolidates 12 distinct data systems and allows users to locate and order data products at eight DAACs (SEDAC will come on line later this year). Through Version 0, users can also link to NOAA's Satellite Active Archive. Version 1, due for release in February 1996, will include all functional elements of the EOSDIS, but not at full capacity. Version 2, due for release in November 1997, will bring the EOSDIS up to full capacity. Minor upgrades between versions will fix small problems, improve specific services and add new products.

Anyone can access the EOSDIS via the Internet with telenet or via modem. One can access Version 0 from a computer that runs UNIX, X-Windows or VT100. Users can search through the EOSDIS archives in a variety of ways: by scientific discipline, satellite or product name. One can limit the search to specific regions on the Earth or specific dates. To help in selection, EOSDIS allows users to preview low-resolution browse images before ordering the data product. Data set descriptions also help users choose applicable products. A help desk at each DAAC takes data orders and troubleshoots problems. Kevin Schaefer is with NASA Headquarters in Washington, DC.