Reproduced, with permission, from:
U.S. Environmental Protection Agency. 1993. North American Landscape Characterization (NALC), Research Brief. Las Vegas, NV: Environmental Monitoring Systems Laboratory
The 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.
Land cover (LC) is the characteristic elements of the earth's surface including vegetation, soil, topography and human features. Typically, changes in land cover occur when agriculture/pasture is converted to urban, or forest to agriculture/pasture. The results as to type of land cover and change in land covers will be valuable as input to U.S. Global Change Research Program (GCRP) measurement and modeling efforts.
NALC products will have an important role in evaluations of land processes and characteristics. Processes refers to actions of the atmosphere, water, and soils that are influential on the earth. These could include changes in trace gas fluxes, and changes in biodiversity.
The goals of the NALC-Pathfinder project are to produce standardized data sets for the majority of the North American Continent. 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 global change research programs.
The NALC project is a component of the National Aeronautics and Space Administration (NASA) Landsat Pathfinder Program. Pathfinder efforts are focused on evaluation of global change using available remote sensor technologies. The results and methodologies from NALC will help address current problems, and establish the "path" to more advanced Earth Observation System (EOS) technologies.
Global change results from alteration of natural atmospheric, oceanic and terrestrial processes. Changes in the quantity and variety of biotic and abiotic components of ecosystems are important global change indicators. Understanding change in natural processes and the influence of human contributions is important to addressing the impact of global climatic effects on ecosystems.
To address these processes and supply information to decision makers, a program of measurements and modeling of land cover conditions and their change will be required. To meet these requirements the U.S. Environmental Protection Agency has initiated the NALC project to provide land cover (LC) determinations and change over time. Study of land cover change along with earth systems processes will allow causative factors and feedback effects to be identified and quantified.
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. In particular, issues of carbon cycling (inventory or pool, carbon release, and sequestration) need to be evaluated at the regional and global scale. Changes in land cover over time are important spatial data to assist in understanding the flux of atmospheric trace gases such as methane and nitrous oxide.
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 (LC). The quantity, variety, and spatial distribution of land cover types are important data inputs for the inventory and modeling of terrestrial carbon stored in geographic regions of interest.
The NALC project has a number of linkages to Global Change Research Programs in EPA, as well as to other Agency domestic efforts and to international programs of global research and inventory. Examples of collaborative efforts include contributions to be made to programs on Deforestation, Biomass Burn Monitoring, Emission Modeling, EPA's Environmental Monitoring and Assessment Program (EMAP), and the Intergovernmental Panel on Climate Change (IPCC).
The NALC global change research project at the Las Vegas Environmental Monitoring Systems Laboratory (EMSL) is a component of the Office of Research and Development's (ORD) national program on global change research. The effort is being conducted as part of the National Aeronautics and Space Administration (NASA) Landsat Pathfinder Program of pilot studies. The goals of these studies are to evaluate existing satellite data for use in current and future satellite sensor programs in support of U.S. and international GCRP efforts. The Landsat Pathfinder Program will also develop some of the methods to archive, process and distribute the future high volume Earth Observation System (EOS) data. Work is being conducted by EPA and other government scientists, university cooperators, and contractor scientists.
In particular, work is being performed in collaboration with several groups. The U.S. Geological Survey EROS Data Center (EDC) is providing support in the areas of data acquisitions, pilot studies of data preprocessing techniques, MSS triplicate data archive and management, and ultimately in the production and dissemination of data sets. This collaboration creates great efficiencies in assembling requisite technical expertise, and allows NALC goals to be achieved with the available resources of EPA.
The Canada Centre for Remote Sensing (CCRS) is also participating in the NALC project. The CCRS efforts will initially focus on the development of methods for the creation of large area image mosaics from NALC MSS Triplicates. Work will initially be concentrated in both the Canadian and U.S. portions of the Great Lakes Watershed.
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 Multispectral Scanner System (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 initial NALC retrospective change detection effort.
Research and development activities will focus on the data products to be generated and organized into data sets for use in GCRP activities. The specific research and development tasks include: a) acquiring Landsat MSS images with less than 30% cloud cover during 1992, b) assembling the individual scenes from 1973, 1986, and 1991, plus or minus one year, to be used for generating coregistered "triplicate" scenes (Figure 1), c) creating triplicate scenes georeferenced to a 60 x 60 meter (m) Universal Transverse Mercator (UTM) ground coordinate grid (Figure 2), d) creating Reduced Cloud Cover Composites (RCCC's) for scenes when necessary (Figure 3), e) generating derivative products from the georeferenced image data, such as land cover categorizations, f) developing capabilities to facilitate archive/management, and distribution of the image data and attendant descriptions of the data or "meta" database, g) disseminating products to global change researchers via EDC, and h) conducting research on important issues such as image categorization and change detection using the NALC data sets.
The georegistered image products will be made available through cooperative research agreements with EPA-EMSL-LV, and at the cost of duplication from USGS-EDC. The MSS database products will be available in whole scenes corresponding to the Landsat World Reference System Two (WRS2) (Figure 1). Procedures have been developed to create high quality georegistered images in which systematic corrections for radiometry (variability in detector response) and geometry (earth rotational skew, picture element or pixel oversampling).
NALC images will be geometrically rectified, georeferenced, and placed into a UTM map projection. Pixels will be 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.
Some efforts will be devoted to developing composites of multiple date Landsat images of the same area. This is necessary as some image scenes will be collected with cloud cover in excess of 30%. These Reduced Cloud Cover Composites or RCCC images (Figure 3) will be made of cloud free portions of images from different dates.
These Reduced Cloud Cover Composites will exhibit some scene variability resulting from changes in the sun's position, atmospheric conditions, vegetation growth patterns or phenology, and other temporal influences. These sources of variability may cause similar materials or land cover types to exhibit dissimilar spectral responses. Portions of this systematic variability may be reduced to facilitate data processing and LC categorizations.
Coregistered, derivative products will be developed and made available along with the original data. These derivative products would include pixel identity images to index pixels of mosaics or Reduced Cloud Cover Composite images (RCCC) to the original input scene (Figure 2). Additional images would include multi-spectral categorization images, and land cover change images.
Data will be distributed to the non-commercial research community by EDC at the nominal cost of reproduction. It is anticipated that products will be available on media or in formats such as nine track magnetic tape, 8mm magnetic tape, and/or 3480 tape cartridges. Later, data may be ordered and delivered through communication networks. In addition, characteristics of these scenes will be incorporated in USGS's "meta" database of satellite image scenes. A UNIX based information management system (IMS) and the Global Land Information System (GLIS) will be available to query data sets that are involved in the Landsat Pathfinder Project. This will allow inventory and archiving of NALC products, as well as facilitate browsing of NALC image scenes, and identification and procurement of suitable products.
Efforts are under way to develop standard procedures for generation and analysis of NALC products. These standard methods for Landsat data analysis are of major importance to the NALC project. The standardization of analytical methods will provide consistent land cover and land cover change products over the North American continent. These standard approaches also address important Agency issues related to data Quality Assurance/Quality Control (QA/QC), such as data validation .
Pilot studies will test and determine the standard land cover (LC) categorization procedures for the project. Methods development projects will evaluate approaches using study areas in forested, agriculture/pasture, and cloud-prone tropical forested areas. An additional, important activity is the formulation and testing of standard change detection procedures using NALC data. These procedures will focus on generation of products useful to measurement and modeling of global change. Results will also yield a series of procedures that can relate anthropogenic or natural causes to land cover change.
These efforts will be accomplished using a variety of federal collaborators and university cooperators. Collaborators include EPA, EMSL-Las Vegas, the USGS EROS Data Center, and other federal agencies. Certain work will require assistance from outside the government, and the contract or Cooperative Agreement vehicles will help to obtain additional capabilities for data processing, and research and development.
Three large pilot studies will test the standard land cover categorization and change detection procedures. One pilot study focuses on the 64,000 square mile Chesapeake Bay Watershed. A second pilot study will evaluate these procedures in the State of Chiapas, Mexico. The third pilot will be conducted in the 150,000 square mile Great Lakes Watershed to evaluate procedures in the north temporate and boreal forest ecoregions. These data analyses and comparative evaluations will lay the ground work for efforts with NALC products.
Several major program outputs are envisioned. By September 1993 a detailed technical plan will be finalized and its elements will be in place. By September 1993 pilot study data sets will be available, and by September 1994 the NALC standard product data sets will be initially available for North America.
International cooperation will involve universities of Mexico, Central America, and the Caribbean. Early work will focus on Southeastern Mexico and issues related to humid tropical forests. Later efforts will involve contributions in the form of research and in the form of ground data collection support activities.
The project goal of developing products from satellite data in support of global change research is a continuing one. A principal aim is to move to a prospective evaluation methodology based on the use of Landsat Thematic Mapper (TM) Data. This will facilitate detailed spectral and spatial analyses of ecosystems and detection of changes in land cover in a contemporary timeframe.
The use of TM data will also facilitate the development of products that represent an entire "swath" of data across the earth's surface. Such a swath would run north to south across the entire continental land mass, and stretch east to west 185 kilometers in width. This product would supply a great deal of data over a large area of the earth in a "same day" timeframe. It is anticipated that these large data sets will be processed in a Supercomputer environment. In addition to change detection efforts, these data sets would be useful in the calibration or verification of results from numerical models, or in support of analyses of AVHRR and Landsat MSS products, which have less spatial and spectral resolution.
Several proposals have been initiated within the Agency to characterize changes in land cover types in North America.
There is also an initiative to acquire data for the coastal Atlantic forests of eastern Brazil, and to do so with a format similar to the NALC program of data acquisition. These efforts and others proposed for Southeast Asia and tropical Africa will extend this land cover analysis approach to additional regions of interest to Global Change researchers.
Points of contacts are Ross Lunetta (702-798-2175), EPA Environmental Monitoring Systems Laboratory - Las Vegas, and James Sturdevant (605-594-6511), USGS-EROS Data Center.
