SAFARI 2000 Tree Cover from AVHRR, 1-KM, 1993 (DeFries et al.) ---------------------------------------- Abstract -------- The data set consists of a southern Africa subset of the 1km Global Tree Cover Data Set developed at the Laboratory for Global Remote Sensing Studies (LGRSS) at the University of Maryland. Characterization of terrestrial vegetation from the Advanced Very High Resolution Radiometer (AVHRR) on the global to regional scale has traditionally been accomplished using classification schemes with discrete numbers of vegetation classes. Representation of vegetation into a limited number of homogeneous classes does not account for the variability within land cover, nor does the portrayal recognize transition zones between adjacent cover types. An alternative paradigm to describing land cover as discrete classes is to represent land cover as continuous fields of vegetation characteristics using a linear mixture model approach. This prototype data set, created by researchers at the Laboratory for Global Remote Sensing Studies (LGRSS) at the University of Maryland, contains 1km cells estimating: 1) Percent tree cover; 2) Percentage cover for two layers representing leaf longevity (evergreen and deciduous); and 3) Percentage cover for two layers estimating leaf type (broadleaf and needleleaf). Data acquired in 1992-93 from NOAA's AVHRR at a 1km spatial resolution and processed under the guidance of the International Geosphere Biosphere Programme (IGBP) were used to derive the tree cover, leaf type and leaf longevity maps. Each pixel in the layers has a value between 10 and 80 percent. These layers can be directly used as parameters in models or aggregated into more conventional land cover maps. For the latter, the product offers the flexibility to derive land cover maps based on user's requirements for a particular application. The product is intended for use in terrestrial carbon cycle models, in conjunction with other spatial data sets such as climate and soil type, to obtain more consistent and reliable estimates of carbon stocks. ========================================================================= Background Information ---------------------- Investigators: Ruth DeFries rd63@umail.umd.edu Matthew Hansen mhansen@Glue.umd.edu John Townshend jt59@umail.umd.edu Anthony C. Janetos Tom Loveland Project: SAFARI 2000 Data Set Title: SAFARI 2000 Tree Cover from AVHRR, 1-KM, 1993 (DeFries et al.) Site: Southern Africa Westernmost Longitude: 5 Easternmost Longitude: 60 Northernmost Latitude: 5 Southernmost Latitude: -35 Start_Date: 1992-01-01 End_Date: 1993-12-31 Data Set Citation: DeFries, R. S., M. Hansen, J. R. G. Townshend, A. C. Janetos, and T. R. Loveland. 2002. SAFARI 2000 Tree Cover from AVHRR, 1-km, 1993 (DeFries 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 (865) 241-3952 Original Data Set Link: http://glcf.umiacs.umd.edu/ ========================================================================= Data File Information --------------------- The Global Land Cover Facility tree cover data set consists of 5 separate ASCII data files, each one with an accompanying binary image file: 1.broadleaf.dat --> percent coverage for leaf type, broadleaf 2.deciduous.dat --> percent coverage for leaf longevity, deciduous 3.evergreen.dat --> percent coverage for leaf longevity, evergreen 4.needleleaf.dat --> percent coverage for leaf type, needleleaf 5.treecover.dat --> percent tree cover ========================================================================= 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. Data values range from 0 to 255 for treecover.dat and from 0 to 80 for the remaining files. Coordinates listed below are in decimal degrees. Rows 4800 Columns 6600 UpLeftX 5 UpLeftY 5 LoRightX 60 LoRightY -35 cellsize 0.008333333 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 files have also been converted into binary image files that can be viewed in any standard image viewing package. The files are single-byte images, no header, 6600 columns by 4800 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: For treecover: 10 - 80 percent tree cover 254 non-vegetated 255 tree cover less than 10% For evergreen, deciduous, broadleaf, and needleleaf 10 - 80 percent cover for indicated leaf longevity and type % evergreen + % deciduous = % tree cover; and % broadleaf + % needleleaf = % tree cover The original data and documentation can be obtained from the Global Land Cover Facility at the University of Maryland: http://glcf.umiacs.umd.edu/