North American Landscape Characterization Project
Principal Investigators: Daniel T. Heggem and Ricardo D. Lopez
U.S. Environmental Protection Agency, Office of Research and
Development, Las Vegas, Nevada 89193-3478.
INTRODUCTION AND OBJECTIVES
The North American Landscape Characterization (NALC) project has been developed to take advantage of historical and current Landsat satellite remote sensor measurements for evaluation of global processes. These efforts involve characterizing land cover types or landscape features, and evaluating their change using satellite sensors.
The goal of the NALC project is to produce standardized digital data sets for the contiguous 48 states and Mexico. The project will develop standard data analysis methods to perform inventories of land cover, quantify land cover change analyses, and produce digital data base products in support of the U.S. and international research programs. Quantifying meaningful measures of landscape characteristics, monitoring of natural processes, and evaluating human influences pose difficult scientific challenges. Global and regional scale monitoring of atmospheric, terrestrial, and aquatic processes, and understanding the linkages of these processes, are required. Changes in land cover over time are important spatial data to assist in understanding the change in natural processes and the influence of human contributions, or its subsequent impact, on ecological condition. To supply information for these evaluations, measurements of variables must be made over large areas of the earth's surface and at suitable increments in time. Satellite remote sensor data are very appropriate as they supply repetitive, consistent, and global measurements for process-related research and modeling. The spectral reflectance characteristics of earth surface materials can be used to quantify the spatial distribution of land cover. The quantity, variety, and spatial distribution of land cover types are important data inputs for the inventory and assessment of changes in ecological condition. The U.S. Environmental Protection Agency, in collaboration with the U.S. Geological Survey EROS Data Center (EDC) and the National Autonomous University of Mexico (UNAM), has initiated the NALC project to provide land cover determinations and change over time. The U.S. Geological Survey EDC is providing support in the areas of data acquisition, data preprocessing, Landsat Multispectral Scanner (MSS) triplicate data archive and management, and production and dissemination of data sets.
To conduct change detection and other analyses over time and space it is best to utilize historical and current data from the same or similar instrument. The Landsat MSS sensor has acquired data from July 1972 through September 1992. These data have been archived in digital form and can be used for quantitative analyses. No other existing sensor system has a digital archive with a long term record of acquisitions over a major portion of the earth. Hence, these data have been selected for use in the NALC project for retrospective change analysis. Specific research and development tasks include: a) acquiring Landsat MSS images with less than 30% cloud cover, b) assembling the individual scenes from 1973, 1986, and 1991, ideally plus or minus one year, to be used for generating co-registered "triplicate" scenes, c) creating triplicate scenes georeferenced to a 60 x 60 meter (m) Universal Transverse Mercator (UTM) ground coordinate grid, d) generating derivative products from the georeferenced image data, such as Normalized Difference Vegetation Index (NDVI) and land cover categorizations, e) developing capabilities to facilitate archive/management, and distribution of the image data and attendant descriptions of the data or "meta" database, f) disseminating products to researchers via EDC, and g) conducting research on important issues such as image categorization, change detection, and landscape indicators using the NALC data sets and landscape ecology as a theoretical base. The MSS database products are available in whole scenes corresponding to the Landsat World Reference System Two (WRS2). The NALC images are geometrically rectified, georeferenced, and placed into a UTM map projection. Pixels have been resampled into a 60m x 60m size format. The 60m x 60m pixel resolution was selected for compatibility with the 30m x 30m Landsat Thematic Mapper (TM) data resolution. Data are distributed on 8mm magnetic tape and CD-ROM. Data may also be ordered and delivered through Internet. The EDC Web Site is available to query data sets, i.e., search inventory and status of NALC products, as well as facilitate browsing of NALC image scenes, and identification and procurement of suitable products.
RELATED EPA EFFORTS
Currently, NALC data products are useful to measuring and relating anthropogenic or natural causes to land cover change in at least two large pilot studies, i.e., Mid-Atlantic Region (northeast U.S.) and San Pedro Watershed (U.S./Mexico). Three-date georeferenced NALC data sets are being utilized to derive either digital land cover maps or generate NDVI spectral coverages for these locations. Ultimately, the NALC data sets and their derivative products are used to generate landscape indicators that relate to composition and pattern metrics. The landscape metrics are used to determine status and trend of ecological and hydrological condition over time (approximately 20 years) and are particularly related to environmental endpoints of concern, such as sustainability, biodiversity, and watershed integrity. Landscape metrics are further used to generate multi-scale assessments and are particularly useful in relating environmental well-being to both man-induced and natural stress.
U.S. Environmental Protection Agency. 1993. North American Landscape Characterization (NALC) Research Brief. EPA/600/S-93/0005, Office of Research and Development, Washington, D.C., 8pp.