SAFARI 2000 Land Cover from AVHRR, 8-km (Hansen et al.) ---------------------------------------------- Abstract -------- This data set consists of a southern Africa subset of the UMD 8 km Global Land Cover product in ASCII GRID format. Over the past several years, researchers have increasingly turned to remotel sensed data to improve the accuracy of data sets that describe the geographic distribution of land cover at regional and global scales. To develop improved methodologies for global land cover classifications as well as to provide global land cover products for immediate use in global change research, researchers at the Laboratory for Global Remote Sensing Studies (LGRSS) at the University of Maryland, have employed the NASA/NOAA Pathfinder Land (PAL) data set with a spatial resolution of 8km. This data set has a length of record of 14 years (1981-1994), providing the ability to test the stability of classification algorithms. Furthermore, this data set includes red, infrared, and thermal bands in addition to the Normalized Difference Vegetation Index (NDVI). Inclusion of these additional bands improves discrimination between cover types. The project aim is to develop and validate global land cover data sets and to develop advanced methodologies for more realistically describing the vegetative land surface based on satellite data. The 8km global land cover product was derived by testing several metrics that describe the temporal dynamics of vegetation over an annual cycle. These metrics were applied to 1984 PAL data at 8km resolution to derive a global land cover classification product using a decision tree classifier. The final product contains 13 land cover classes. The 8km global land cover product is available for download from the Global Land Cover Facility (GLCF) web site. The data are provided as UNIX compressed files in a choice of two formats: 1) BSQ binary Goodes projection and 2) BSQ binary lat/long projection (Plate Carree projection). Additional information and references on this data set can be found at the GLCF web site as well as at the LGRSS web site (link provided at the GLCF web site ) and in the readme files found along with the data. ===================================================================== ==== Background Information ---------------------- Investigators: Matthew Hansen mhansen@Glue.umd.edu Ruth DeFries rd63@umail.umd.edu John Townshend jt59@umail.umd.edu Rob Sohlberg rsohlber@geog.umd.edu Project: SAFARI 2000 Data Set Title: SAFARI 2000 Land Cover from AVHRR, 8-km (Hansen et al.) Site: Southern Africa Westernmost Longitude: 5 Easternmost Longitude: 60 Northernmost Latitude: 5 Southernmost Latitude: -35 Start Date: 1984-01-01 End_Date: 1984-12-31 Data Set Citation: Hansen, M., R. S. DeFries, J. R. G.Townshend, and R. Sohlberg. 2002. SAFARI 2000 Land Cover from AVHRR, 8-km (Hansen et al.). Available on-line [http://www.daac.ornl.gov/] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. Southern African subset extractions of this data were performed by Oak Ridge National Laboratory: ORNL DAAC User Services Office ornldaac@ornl.gov +1 (423) 241-3952 Original Data Set Link: http://glcf.umiacs.umd.edu/ ===================================================================== ==== ASCII File Information ---------------------- The data files are in ASCII Grid format for ArcInfo. More information on this format is contained within the README file (link provided above). Each file contains a single ASCII array with integer values. Coordinates listed below are in decimal degrees. Rows 640 Columns 880 UpLeftX 5 UpLeftY 5 LoRightX 60 LoRightY -35 cellsize 0.0625 Projection geographic The ASCII file consists of header information containing a set of keywords, followed by cell values in row-major order. The file format is: {NCOLS xxx} {NROWS xxx} {XLLCORNER xxx} {YLLCORNER xxx} {CELLSIZE xxx} {NODATA_VALUE xxx} row 1 row 2 . . . row n where xxx is a number, and the keyword NODATA_VALUE is optional and defaults to -9999. Row 1 of the data is at the top of the grid, row 2 is just under row 1 and so on. The end of each row of data from the grid is terminated with a carriage return in the file. To import this file into ArcInfo use the following command at an ARC prompt: ASCIIGRID {in_ascii_file} {out_grid} {INT | FLOAT} Arguments: {in_ascii_file} - the ASCII file to be converted. {out_grid} - the name of the grid to be created. {INT | FLOAT} - the data type of the output grid. INT - an integer grid will be created. FLOAT - a floating-point grid will be created. Binary File Information ----------------------- The ASCII data file has also been converted into a binary image file that can be viewed in any standard image viewing package. The file is a single-byte image, no header, 880 columns by 640 rows. Missing data (ASCII -9999) have been converted to the maximum value of 255. File Compression Information ---------------------------- For this archive, the data files have been compressed with the MS Windows-standard Zip compression scheme. These files were compressed using Aladdin's DropZip on a Macintosh. DropZip uses the Lempel-Ziv algorithm, also used in Zip and PKZIP programs. The compressed files may be uncompressed using PKZIP (with the -expand option) on MS Windows and UNIX, or with StuffIt Expander on the Mac OS. You can get newer versions from the PKZIP Web site at http://www.pkware.com/shareware/. ===================================================================== ==== Procedure Used to Create the Southern Africa Subset --------------------------------------------------- The original data were obtained and read following the directions in the original documentation. The data were converted to ASCII arrays and then imported into ArcInfo using the ASCIIGRID command. Using GRID (a raster- or cell-based geoprocessing toolbox that is integrated with ArcInfo) the SETWINDOW command was used to define the subarea of interest. This subarea was defined by identifying the bounding coordinates as follows: x_min 5 y_min -35 x_max 60 y_max 5 The "snap_grid" option of the SETWINDOW command was used. This snaps the lower-left corner of the specified window to the lower-left corner of the nearest cell in the snap_grid and snaps the upper-right corner of the specified window to the upper-right corner of the nearest cell in the snap_grid. In this case the snap_grid is an original data grid. The purpose of this is to ensure the proper registration of the newly set analysis window. The command format used is as follows: SETWINDOW x_min y_min x_max y_max original_grid Once the window was set, creating the new grid was simply a matter of setting the new subset grid equal to the original grid. subset_grid = original_grid An ASCII array was created from the new subset grid using the GRID command GRIDASCII. file.dat = GRIDASCII(subset_grid) ===================================================================== ==== Legend & Additional Sources of Information ------------------------------------------ The following legend is used in the original data set: 0 Water 1 Evergreen needleleaf forests 2 Evergreen broadleaf forests 3 Deciduous needleleaf forests 4 Deciduous broadleaf forests 5 Mixed forests 6 Woodlands 7 Wooded grasslands/shrubs 8 Closed bushlands or shrublands 9 Open shrublands 10 Grasses 11 Croplands 12 Bare 13 Mosses and lichens Although not all of these categories may be represented in the subset of the data, the original legend has been retained. The original data and documentation can be obtained from the Global Land Cover Facility at the University of Maryland: http://glcf.umiacs.umd.edu/