BOREAS Regional DEM in Raster Format and AEAC Projection Summary This data set is based on the GTOPO30 DEM produced by the USGS EDC. The BOREAS region (1,000km x 1000km) was extracted from the GTOPO30 data and reprojected by BOREAS staff into the AEAC projection. The pixel size of these data is 1 km. The data are stored in binary, image format files. Note that the binary files of this data set on the BOREAS CD-ROMs have been compressed using the Gzip program. See section 8.2 for details. Table of Contents * 1 Data Set Overview * 2 Investigator(s) * 3 Theory of Measurements * 4 Equipment * 5 Data Acquisition Methods * 6 Observations * 7 Data Description * 8 Data Organization * 9 Data Manipulations * 10 Errors * 11 Notes * 12 Application of the Data Set * 13 Future Modifications and Plans * 14 Software * 15 Data Access * 16 Output Products and Availability * 17 References * 18 Glossary of Terms * 19 List of Acronyms * 20 Document Information 1. Data Set Overview 1.1 Data Set Identification BOREAS Regional DEM in Raster Format and AEAC Projection 1.2 Data Set Introduction This data set is based on the GTOPO30 global Digital Elevation Model (DEM) produced by the United States Geological Survey (USGS) Earth Resources Observation System (EROS) Data Center (EDC). The area covering the BOReal Ecosystem-Atmosphere Study (BOREAS) region (1,000km x 1,000km) was extracted from the GTOPO30 data and reprojected by BOREAS staff into the BOREAS grid projection. The pixel size of these data is 1km. The GTOPO30 data set produced by EDC is in latitude/longitude and has a pixel size of 30 arc seconds. The GTOPO30 data set is available from the EDC Distributed Active Archive Center (DAAC). 1.3 Objective/Purpose These data are provided as part of the BOREAS Staff Science GIS Data Collection Program that included the collection of pertinent map data, in both hard copy and digital form. The purpose of this data set is to provide users with a data product that characterizes the topography of the BOREAS Region. This data set is to be used for modeling purposes at a regional scale. 1.4 Summary of Parameters Elevation above mean sea level 1.5 Discussion None. 1.6 Related Data Sets BOREAS HYD-08 DEM Data over the NSA-MSA and SSA-MSA in the UTM Projection BOREAS DEM Data over the NSA-MSA and SSA-MSA in the AEAC Projection GTOPO30 Global 30 Arc Second Elevation Data Set (available at http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html) (tiles W100N90 and W140N90 of GTOPO30 cover the BOREAS region) 2. Investigator(s) 2.1 Investigator(s) Name and Title David E. Knapp BOREAS Information System Staff Member 2.2 Title of Investigation BOREAS Staff Science GIS Activities 2.3 Contact Information Contact 1 ---------- David E. Knapp NASA/GSFC Greenbelt, MD (301) 286-1424 (301)286-0239 (fax) David.Knapp@gsfc.nasa.gov Contact 2 ----------- Kristine Verdin USGS/EROS Data Center Sioux Falls, SD (605) 594-6002 kverdin@dg1.cr.usgs.gov 3. Theory of Measurements This data product was reprojected from a DEM product by EDC. It is intended to represent the terrain at a regional scale. 4. Equipment Users of this data set are referred to the EDC DAAC to obtain background information on how these data were compiled. 4.1 Sensor/Instrument Description Unknown. 4.1.1 Collection Environment Unknown. 4.1.2 Source/Platform Unknown. 4.1.3 Source/Platform Mission Objectives Unknown. 4.1.4 Key Variables Elevation above mean sea level 4.1.5 Principles of Operation Unknown. 4.1.6 Sensor/Instrument Measurement Geometry Unknown. 4.1.7 Manufacturer of Sensor/Instrument Unknown. 4.2 Calibration Unknown. 4.2.1 Specifications Unknown. 4.2.1.1 Tolerance Unknown. 4.2.2 Frequency of Calibration Unknown. 4.2.3 Other Calibration Information 5. Data Acquisition Methods The original data were acquired from personnel at the USGS EDC. EDC personnel used Digital Terrain Elevation Data (DTED) from Canada and resampled it to 30 arc seconds using a nearest neighbor resampling method. Any areas that were not covered by DTED were filled in with gridded contour data from the Digital Chart of the World (DCW). These data were gridded by EDC using the TOPOG software package. The stream network from the DCW was used for drainage enforcement. The data covering the BOREAS region were extracted from the EDC DEM by BOREAS Information System (BORIS) staff and reprojected into the BOREAS grid projection. 6. Observations 6.1 Data Notes Unknown. 6.2 Field Notes Unknown. 7. Data Description 7.1 Spatial Characteristics 7.1.1 Spatial Coverage The area covered by this DEM is a 1,000 km x 1,000 km area that roughly straddles the Manitoba-Saskatchewan border in Canada. The outside corners of the corner pixels of the data set are as follows: The North American Datum 1983 (NAD83) corner coordinates of the BOREAS region are: BOREAS Corner Latitude Longitude X (km) Y (km) ------------------------------------------------------------ Northwest 58.979 N 111.000 W 0.000 1000.000 Northeast 58.844 N 93.502 W 1000.000 1000.000 Southwest 51.000 N 111.000 W 0.000 0.000 Southeast 50.089 N 96.969 W 1000.000 0.000 7.1.2 Spatial Coverage Map Not available. 7.1.3 Spatial Resolution These data were gridded to a cell size of 1,000 meters in both the X and Y directions. 7.1.4 Projection The area mapped is projected in the BOREAS grid projection, which is based on the ellipsoidal version of the Albers Equal Area Conic (AEAC) projection. The projection has the following parameters: Datum: NAD83 Ellipsoid: GRS80 or WGS84 Origin: 111.000°W 51.000°N degrees Standard Parallels: 52° 30' 00"N 58° 30' 00"N Units of Measure: kilometers 7.1.5 Grid Description 7.2 Temporal Characteristics 7.2.1 Temporal Coverage Not applicable 7.2.2 Temporal Coverage Map Not available. 7.2.3 Temporal Resolution The sources of data produced by EDC were from different dates. The temporal characteristics of these data are insignificant, considering the fact that these are elevation data at a very coarse scale (a pixel is 1,000m x 1,000m). 7.3 Data Characteristics 7.3.1 Parameter/Variable Elevation above mean sea level 7.3.2 Variable Description/Definition Elevation above mean sea level - The vertical distance between a plane at mean sea level and a parallel plane intersecting the given geographic point. 7.3.3 Unit of Measurement Meters 7.3.4 Data Source The original data were acquired from personnel at the USGS EDC. 7.3.5 Data Range Not available. 7.4 Sample Data Record Not applicable to binary raster images. 8. Data Organization 8.1 Data Granularity The smallest amount of data that can be ordered from this data set is the entire data set covering the entire BOREAS region. 8.2 Data Format(s) 8.2.1 Uncompressed Data Files The data product contains two files: File 1: ASCII header file containing 8 records of 80 bytes. File 2: DEM data file consisting of 1,000 records containing 2,000 bytes each. Each 2,000-byte record is an image line and contains 1,000 2-byte (16-bit) integers stored as low-order byte first. 8.2.2 Compressed CD-ROM Files On the BOREAS CD-ROMs, file 1 is stored as ASCII text; however, file 2 has been compressed with the Gzip compression program (file name *.gz). These data have been compressed using gzip version 1.2.4 and the high compression (-9) option (Copyright (C) 1992-1993 Jean-loup Gailly). Gzip (GNU zip) uses the Lempel-Ziv algorithm (Welch, 1994) used in the zip and PKZIP programs. The compressed files may be uncompressed using gzip (-d option) or gunzip. Gzip is available from many websites (for example, ftp site prep.ai.mit.edu/pub/gnu/gzip-*.*) for a variety of operating systems in both executable and source code form. Versions of the decompression software for various systems are included on the CD-ROMs. 9. Data Manipulations 9.1 Formulae 9.1.1 Derivation Techniques and Algorithms As stated in Section 5, these data were reprojected from latitude/longitude coordinates to the BOREAS grid projection. The BOREAS grid is based on the ellipsoidal version of the AEAC projection as defined within the NAD83. The parameters used for this projection are given in Section 7.1.4. A nearest neighbor resampling method was used in reprojecting the data. 9.2 Data Processing Sequence 9.2.1 Processing Steps BORIS staff processed the data by: 1) Extracting the DEM from EDC into ARC/INFO grid. 2) Creating a projection file to define input (latitude/longitude) and output (AEAC) projections. 3) Reprojecting the original DEM into the AEAC projection using the ARC/INFO PROJECT command. 4) Writing the reprojected data file to tape. 5) Copy the ASCII and compress the binary files for release on CD-ROM. 9.2.2 Processing Changes None. 9.3 Calculations 9.3.1 Special Corrections/Adjustments None. 9.3.2 Calculated Variables None. 9.4 Graphs and Plots None. 10. Errors 10.1 Sources of Error The TOPOG program interpolates the values to grid cells from vector data (digitized contours). Errors occur where the original vector data are too sparse spatially, e.g., in flat lowland areas. 10.2 Quality Assessment No quality assessment is available; therefore, caution is advised to those who use this product. 10.2.1 Data Validation by Source Not available. 10.2.2 Confidence Level/Accuracy Judgment Not available. 10.2.3 Measurement Error for Parameters Not available. 10.2.4 Additional Quality Assessments Not available. 10.2.5 Data Verification by Data Center After extracting and reprojecting the data, BORIS staff displayed and visually reviewed the data. No anomalies or errors were detected in this review. 11. Notes 11.1 Limitations of the Data Elevation variations can exist within the lakes, especially large lakes, due to the reason given in Section 10.1. 11.2 Known Problems with the Data See Sections 10.1 and 11.1. 11.3 Usage Guidance It is important for the user to keep in mind that this data set is at a coarse scale and might not be useful at other scales. Before uncompressing the Gzip files on CD-ROM, be sure that you have enough disk space to hold the uncompressed data files. Then use the appropriate decompression program provided on the CD-ROM for your specific system. 11.4 Other Relevant Information The original EDC GTOPO30 Global 30 Arc Second Elevation Data Set is available at http://edcwww.cr.usgs.gov/landdaac/gtopo30/ (map tiles W100N90 and W140N90 of GTOPO30 cover the BOREAS region). 12. Application of the Data Set These data could be used by anyone needing elevation data at coarse resolutions over large areas. 13. Future Modifications and Plans None. 14. Software 14.1 Software Description The data manipulation capabilities in the ARC/INFO software package (Version 7.0) were used to reproject the data. ARC/INFO is a GIS package developed by the Environmental Systems Research Institute, Inc. (ESRI). Gzip (GNU zip) uses the Lempel-Ziv algorithm (Welch, 1994) used in the zip and PKZIP commands. 14.2 Software Access ARC/INFO is a proprietary software package produced byESRI: Environmental Systems Research Institute, Inc. 380 New York St. Redlands, CA 92373-8100 Gzip is available from many websites across the net (for example) ftp site prep.ai.mit.edu/pub/gnu/gzip-*.*) for a variety of operating systems in both executable and source code form. Versions of the decompression software for various systems are included on the CD-ROMs. 15. Data Access 15.1 Contact Information Ms. Beth Nelson BOREASData Manager NASA/GSFC Greenbelt, MD (301) 286-4005 (301) 286-0239 (fax) Elizabeth.Nelson@gsfc.nasa.gov 15.2 Data Center Identification See Section 15..1 15.3 Procedures for Obtaining Data Users may place data requests by telephone, electronic mail, or fax. 15.4 Data Center Status/Plans The regional DEM data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The BOREAS contact at ORNL is: Merilyn Gentry User Services/Data Coordinator Oak Ridge National Laboratory DAAC Oak Ridge, TN (423) 241-3952 ornldaac@ornl.gov 16. Output Products and Availability 16.1 Tape Products The DEM data can be made available on 8-mm, Digital Archive Tape (DAT), or 9- track tapes at 6250 or 1600 Bytes Per Inch (BPI). 16.2 Film Products None. 16.3 Other Products These data are available on the BOREAS CD-ROM series. 17. References 17.1 Platform/Sensor/Instrument/Data Processing Documentation Snyder, J.P. 1987. Map Projections - A Working Manual. USGS Professional Paper 1395. TOPOG User Guide (Version 5.0). 1994. Division of Water Resources, CSIRO. Canberra, Australia. Welch, T.A. 1984, A Technique for High Performance Data Compression, IEEE Computer, Vol. 17, No. 6, pp. 8 - 19. 17.2 Journal Articles and Study Reports Sellers, P., F. Hall. 1994. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1994-3.0, NASA BOREAS Report (EXPLAN 94). Sellers, P., F. Hall. 1996. Boreal Ecosystem-Atmosphere Study: Experiment Plan. Version 1996-2.0, NASA BOREAS Report (EXPLAN 96). Sellers, P., F. Hall, and K.F. Huemmrich. 1996. Boreal Ecosystem-Atmosphere Study: 1994 Operations. NASA BOREAS Report (OPS DOC 94). Sellers, P., F. Hall, and K.F. Huemmrich. 1997. Boreal Ecosystem-Atmosphere Study: 1996 Operations. NASA BOREAS Report (OPS DOC 96). Sellers, P., F. Hall, H. Margolis, B. Kelly, D. Baldocchi, G. den Hartog, J. Cihlar, M.G. Ryan, B. Goodison, P. Crill, K.J. Ranson, D. Lettenmaier, and D.E. Wickland. 1995. The boreal ecosystem-atmosphere study (BOREAS): an overview and early results from the 1994 field year. Bulletin of the American Meteorological Society. 76(9):1549-1577. Sellers, P., F. Hall. 1997. BOREAS Overview Paper. JGR Special Issue (in press). 17.3 Archive/DBMS Usage Documentation None. 18. Glossary of Terms None. 19. List of Acronyms AEAC - Albers Equal Area Conic BOREAS - BOReal Ecosystem-Atmosphere Study BORIS - BOREAS Information System BPI - Bytes Per Inch DAAC - Distributed Active Archive Center DCW - Digital Chart of the World DAT - Digital Archive Tape DTED - Digital Terrain Elevation Data DEM - Digital Elevation Model EDC - EROS Data Center EOS - Earth Observing System EOSDIS - EOS Data and Information System EROS - Earth Resources Observation System ESRI - Environmental Systems Research Institute, Inc. GSFC - Goddard Space Flight Center NAD27 - North American Datum of 1927 NAD83 - North American Datum of 1983 NASA - National Aeronautics and Space Administration NSA - Northern Study Area ORNL - Oak Ridge National Laboratory PANP - Prince Albert National Park SSA - Southern Study Area URL - Uniform Resource Locator USGS - United States Geological Survey UTM - Universal Transverse Mercator 20. Document Information 20.1 Document Revision Dates Written: 17-Mar-1995 Last Updated: 30-Jul-1998 20.2 Document Review Dates BORIS Review: 05-Jun-1997 Science Review: 20.3 Document ID 20.4 Citation The efforts of the BORIS staff in making this data available are greatly appreciated. 20.5 Document Curator 20.6 Document URL Keywords -------------------- DIGITAL ELEVATION MODEL DEM TERRAIN ELEVATION Region_AEAC_DEM.doc 08/18/98