CIESIN Reproduced, with permission, from: National Aeronautics and Space Administration (NASA). 1993. Earth Observing System (EOS) Reference Handbook, ed. G. Asrar and D. J. Dokken. Washington, D. C.: National Aeronautics and Space Administration, Earth Science Support Office, Document Resource Facility.

PATHFINDER DATA SETS


The Pathfinder data set concept was initiated by the EOS Program Office at NASA Headquarters in answer to the question "What can be done now to further global change research?" Pathfinders will provide access to large remote-sensing data sets applicable to global change research prior to the availability of data from the EOS satellites. From these long time-series of global and/or regional data sets, higher level geophysical products will be derived in support of USGCRP objectives. The main goal of the Pathfinder Program is to make research-quality global change data sets easily available to the Earth science community. Of course, experience gained in processing/ reprocessing, archiving, and distributing standard scientific data products proves a boon as well. As scientific understanding develops and product retrieval algorithms are improved, these data sets may require additional reprocessing, which would be provided by this program.

All Pathfinder data sets involve space-based observations, and are subject to the following requirements: 1) Stable calibration of the raw data should be attainable; 2) when data from multiple instruments are involved, consistent intercalibration among instruments in a series should be possible; and 3) archive may include transferring the data to a more accessible medium. Pathfinder activities include reprocessing of these data using community-consensus algorithms as recommended by designated Science Working Groups (SWGs). The resultant data sets will be available through DAACs under EOSDIS Version O.

A Benchmark Period (April 1987 to November 1988) has been chosen to facilitate complementary analyses and intercomparison studies. Wherever possible or applicable, Pathfinder data processing will begin with this time period. In pursuit of the most efficient processing method, different procedures may take place at separate facilities, requiring data transfer among them.

In October 1990, NOAA and NASA signed an agreement establishing three joint NASA/NOAA Pathfinders to be generated from existing NOAA data sets, as follow:

In 1991, the Special Sensor Microwave/Imager (SSM/I) data set was added as a NASA/NOAA Pathfinder. SSM/I data are currently archived by NOAA under a Shared Processing Agreement with the Navy and the Air Force. Landsat Multispectral Scanner (MSS) and Thematic Mapper (TM) data--held primarily by USGS/EDC--were added to the Pathfinder activity in 1992. The Landsat Pathfinder effort involves NASA, EPA, and USGS. Also in 1992, NASA's Scanning Multispectral Microwave Radiometer (SMMR) data set was added as the first NASA-only Pathfinder. Other existing data sets are currently being evaluated to determine their utility within the overall objectives of the multiagency Pathfinder Program.

One or more SWGs have been formed for each of the identified data sets to provide recommendations for specific Pathfinder activities. SWG reports to the involved partner agencies consist of the following:

Pathfinder data products will be treated as new data sets and will be archived at one or more EOSDIS DAACs according to discipline responsibilities. Copies will also be archived by the collaborating agencies. Table 9 lists the current Pathfinder efforts and the DAACs currently planning to house the reprocessed data.

AVHRR Pathfinder scientific data products consist of global vegetation and radiance data for the land community, global sea-surface temperature data for the ocean community, and global clouds, radiation, and aerosols data for the atmospheric sciences community.

These data are produced from GAC observations made by the five channel AVHRR instruments onboard NOAA-7/9/11, and will cover the time period of mid-l981 through 1992 and beyond. Processing of land, ocean, and atmosphere products is scheduled to begin in FY1993, with the land products processing beginning in February 1993. The AVHRR Level 1B GAC data that serves CIS the processing input (including new calibration tables designed to stabilize the calibration and provide inter-instrument calibration) are also a Pathfinder product. Transcription teams at NASA and NOAA have copied more than 30,000 magnetic tapes to almost 400 optical disks, each holding 6 GB of data. This effort was completed at the end of l992.

A Pathfinder study concerning the quality of existing GOES data has been completed, and a summary report is being prepared. An intensive development effort is underway at the University of Wisconsin's Space Science and Engineering Center (SSEC) to create a product generation system that can ingest data at 3.6 times the present real-time capability. Initial GOES Pathfinder product generation will begin in the spring of 1993.

A TOVS implementation team meeting was held in June 1992. A set of geophysical parameters for specific spatial/temporal scales was selected for inclusion into the NOAA-l0 Benchmark Period data set. In addition, it was decided that the Level 3 products from the first month of the period (i.e., April 1987) will be used as a quality check using three distinct processing methodologies: Path A at GSFC, Path B at the Laboratoire de Meteorologie Dynamique/Atmospheric Radiation Analysis Group (LMD/ARA) at Ecole Polytechnique in Paris, France, and Path C at both NOAA/NESDIS and Marshall Space Flight Center (MSFC). Thereafter, the remaining 19 months of the Benchmark Period data will be processed by the four teams by September 1993, for intercomparison and validation of the results. The GSFC DAAC will archive and distribute final products.

The SSM/I Pathfinder will create a suite of products at both Levels 2 and 3. The Level 1 antenna temperatures will be converted to Hierarchical Data Format (HDF), and the swath products will be generated at MSFC beginning in February 1993; the Level 3 gridded products will be generated at the National Snow and Ice Data Center (NSIDC) in July 1993. Archive of the product suites will vary by discipline interest in specific products. A CD-ROM containing selected products is planned for early distribution.

The goal of the Landsat Land (over Pathfinder effort is to establish long-term, medium-to high-resolution data sets for particular regional and global applications to global change research. The Landsat Pathfinder SWG has defined several projects to address land cover change. Within the Tropical Deforestation Project, NASA and EPA are funding selected universities to produce a 3-epoch forest/no-forest data set showing areas of deforestation, derived from each of the moist tropical forested regions (i.e., the Amazon, Central Africa, and Southeast Asia). EPA has taken the lead in a second project to produce 3 epochs of wall-to-wall coverage of conterminous North America. The Pathfinder Program expects to create additional data sets related to global change monitoring issues in such areas as biology, ecology, geology, hydrology, atmospheric sciences, and social sciences. Lastly, work is underway to compile time-series data sets of selected sites chosen because of historical data richness or for other characteristics contributing to global change research.

A Pathfinder Interuse Workshop was held in July 1992, to determine standards and to identify solutions to problems associated with formats, projections, resolution, and binninq; the objective was to facilitate Pathfinder data product integration. The workshop resulted in the resolve to use, when possible, the EOSDIS Version 0 prototype standard (i.e., HDF) as the common data format. A smaller technical group is being formed to work intensively on the remaining problems of binning, resolution, and projection, with results expected in 1 to 2 years.