NASA initiated the Landsat Pathfinder data set in 1991, with the intent of reconfiguring selected portions of the global Landsat data archive to optimize use of Landsat data for global change research. The historical archive consists of 21 years of Landsat Multispectral Scanner (MSS) data at a spatial resolution of 80 meters, and 11 years of Landsat Thematic Mapper (TM) data at a spatial resolution of 30 meters. The Landsat Pathfinder Program Definition Phase Report [not yet available] provides a complete description of the Landsat Pathfinder concept and component activities (publication expected late 1994).
The Landsat Pathfinder data set currently includes three component efforts. The first is the Humid Tropical Forest Inventory Project, which is associated with developing a complete three-epoch, consistently processed Landsat database for the humid, tropical forests of the Amazon Basin, Central Africa, and Southeast Asia. The three epochs are generally the early- to mid-1970s, mid-1980s, and the early 1990s. For each epoch, a set of Landsat scenes will be selected on the basis of minimal cloud cover and acceptable data quality to provide complete coverage of the humid, tropical forest regions. This data set is intended for evaluation of the rate and extent of tropical deforestation.
The second effort is the North American Land Characterization (NALC) Project, which will bring together three epochs of historical Landsat MSS data in a standard configuration for much of the land surface of the North American continent, according to the Environmental Protection Agency research brief (1993) North American Landscape Characterization. The three epochs include the early- to mid-1970s, mid-1980s, and the early 1990s. The database will consist of Landsat MSS scenes from each epoch that are georeferenced at 60-m spatial resolution and coregistered to form a "temporal triplet." Some 800 triplets will be produced to provide complete coverage of the conterminous United States, Alaska, Hawaii, Mexico, Central America, and the Caribbean Islands. Land elevation data, also at 60-m resolution, will be included with each triplet. Additional data products to be derived and included in the database will include computer-categorized land cover from the 1990s MSS scenes and land-cover change data sets computed for each of the intervals between epochs.
Canadian participation in the NALC Project, under the leadership of the Canada Center for Remote Sensing (CCRS), will initially result in the development of a 50-m MSS mosaic of the Great Lakes Watershed. Subsequent expansion of the NALC Project methodology throughout Canada is yet to be determined.
The objective of the third effort, the Land Cover Test Site Project, is to develop existing and future Landsat data into a long term multiepoch and multiseasonal data set for a selected group of test sites distributed around the globe. Test sites will be chosen to represent a wide range of land-cover types with additional characteristics such as availability of historical data, ongoing field-based monitoring programs, and interest to the international global change research community. For each of the test sites, existing correlative data such as AVHRR 1-km data sets, digital elevation data, soils and vegetation data, and aircraft photography will be assembled. Development of this data set is intended to support the development of algorithms for land information to be used with Earth Observing System (EOS) instrument data and for validating land-cover databases generated from continental- and global-scale coarse-resolution satellite image data.
Development of the component projects comprising the Landsat Pathfinder Data Set should offer significant technological and cost advantages to scientists studying the human dimensions of global change. From a technological perspective, Landsat Pathfinder data products will provide already prepared and consistently processed, multidate, georeferenced satellite image data of high spatial resolution effective for documenting and evaluating many of the types, extents, and changes in human activities at local scales. The large regional coverage of the data sets should allow comparison of the results of various local studies for equivalent spatial scales and temporal periods. In "The Benefits of the Landsat Pathfinder Program," Sadowski, Roller, and Colwell (1993) discuss the program's benefits for meeting conceptual and methodological challenges facing social scientists studying the human dimensions of global change.
Currently, the data purchase and processing costs of the Landsat Pathfinder Data Set are funded principally by U.S. Government agencies, including the National Aeronautics and Space Administration, the Environmental Protection Agency, and the U.S. Geological Survey Earth Resources Observation Systems Data Center (EDC). All data sets and derived products will be archived within the Land Processes Distributed Active Archive Center (DAAC) at EDC and distributed to the noncommercial research community at the nominal cost of reproduction.