30 arc-second DEM for Antarctica
Entry ID: GNVd0189_104

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Summary
Abstract: PLEASE NOTE: This is a beta release of the Antarctica DEM. If any data
anomalies are noticed, please send an E-mail to either Mike Oimoen at:
oimoen@dgl.cr.usgs.gov, or Sue Jenson at: jenson@dg1.cr.usgs.gov.
We will look into them, and they may be addressed in the next release.

The Antarctica data is provided in two projections.
Antarctic DEM in geographic (lat/lon) coordinates: 30 arc-second spacing
-ant_dem_lkms1 UL = 180 W, 60S. LR = 90W, 90S (3600 rows x 10800
columns)
-ant_dem_lkms2 UL = 90 W, 60S. LR = 0W, 90S (3600 rows x 10800 columns)
-ant_dem_1kms3 UL = 0 W, 60S. LR = 90E, 90S (3600 rows x 10800 columns)
-ant_dem_1kms4 UL = 90 E, 60S. LR = 180E, 90S (3600 rows x 10800 columns)

Antarctic DEM in polar stereographic coordinates (meters)
-ant_dem_1kmps UL = -2700000 x 2699000. LR = 2699000 x -2700000 (5400 rows x
5400 columns)

Note: Both DEMs are referenced to the WGS84 ellipsoid. The standard latitude of
the polar stereographic DEM is 71S, and it central meridian is 0.

Data Organization: Data are distributed as 16-bit straight raster image files
in a latitude/ longitude coordinate system, and also in a polar stereographic
coordinate system.

Image files are identified by the .bil.gz extension. Each image file of the
Antarctica data set is compressed using the GNU "gzip" utility. If you do not
have access to gzip, the FTP server will uncompress the file as you retrieve
it. To do this, simply leave off the ".gz" extension when retrieving the file
(NOTE: This option is not available through MOSAIC). For example, to retrieve
the file "af_1k_dem1.bil.gz" without compression just use "get
af_dem_lks1.bil". Note that the uncompressed files are typically five times
larger than the compressed versions and so will take five times longer to
transmit. The gzip program is available via anonymous FTP at the following
sites: prep.ai.mit.edu:/pub/gnuwuarchive.wustl.edu:/systems/gnu

Each image file is accompanied by five ancillary files (header file, world
file, statistics file, coordinate file, and data descriptor
record ). The format of each ancillary file is described below:

Header File (.hdr) - The header file can be used as input to the ARC/INFO Image
Integration application. Information contained within this file can also be
used with other image display packages such as IMDISP. The header file is
named after the image with an .hdr extension. The following list identifies
the keywords used in the header file (ARC/INFO User's Guide, Image Integration,
5-4 to 5-10):

byteorder: byte order in which image pixel values are stored
M = Motorola byte order (high order byte first--Sun, HP, etc.)
layout: organization of the bands in the file
bil = band interleaved by line (note: single band image.
This field is required for image integration in ARC/INFO.
nrows: number of rows in the image
ncols: number of columns in the image
nbands: number of spectral bands in the image (will always be 1)
nbits: number of bits per pixel (will always be 16)
bandrowbytes: number of bytes per band per row (will always be double
the number of columns)
totalrowbytes: total number of bytes of data per row (will always be
double the number of columns)
bandgapbytes the number of bytes between bands in a BSQ format image,
the default is 0.
nodata: value used for masking purposes (will be ignored by the Image
Integration application; it is not a standard ARC/INFO keyword)
ulxmap: longitude of the center of the upper-left pixel
ulymap: latitude of the center of the upper-left pixel
xdim: x dimension of a pixel in geographic units (decimal degrees)
ydim: y dimension of a pixel in geographic units (decimal degrees)

Example Header file:

byteorder M
layout BIL
nrows 2410
ncols 2401
nbands 1
nbits 16
bandrowbytes 4802
totalrowbytes 4802
nodata -999
bandgapbytes 0
nodata -9999
ulxmap 30.0000000000000000000000000
ulymap 20.0000000000000000000000000
xdim 0.0083333333333333285900000
ydim 0.0083333333333333285900000

World File (.bilw) - The world file can be used for image-to-world
transformation when displaying an image using the ARC/INFO Geographic
Information System (GIS) Image Integration routine. The world file is named
after the image with a .blw extension. The following is an example of a world
file with a description of each record (ARC/INFO User's Guide, Image
Integration, 2-3 to 2-5):

Description
-----------
0.0083333333333333285900000 xdim x dimension of a pixel in geographic
units
0.0000000000000000000000000 rotation term (will always be zero)
0.0000000000000000000000000 rotation term (will always be zero)
-0.0083333333333333285900000 negative y-scale; dimension of a pixel in
geographic units
30.0000000000000000000000000 longitude of the center of the upper-left
pixel
20.0000000000000000000000000 (latitude of the center of the upper-left
pixel)

Note: ARC/INFO will ignore ulxmap, ulymap, xdim, and ydim in header file if a
world file is present during ingest.

The Statistics File (.stx) - The statistics file contains the band number, the
minimum pixel value (elevation expressed in feet above mean sea level), the
maximum pixel value, the mean, and the standard deviation. The statistics file
is named after the image with an .stx extension.

Example Statistics File:

1 489.0 8427.0
2875.5212789045699500000000000 1179.4763719888228400000000000

The Coordinate File (.tik) - The coordinate file is named after the image with
a .tik extension. The following list identifies the keywords used in the
coordinate file.

ulxmap: longitude of the center of the upper-left pixel
ulymap: latitude of the center of the upper-left pixel
urxmap: longitude of the center of the upper-right-pixel
urymap: latitude of the center of the upper-right-pixel
llxmap: longitude of the center of the lower-left-pixel
llymap: latitude of the center of the lower-left-pixel
lrxmap: longitude of the center of the lower-right-pixel
lrymap: latitude of the center of the lower-right-pixel
xdim: x dimension of a pixel in geographic units (decimal degrees)
ydim: y dimension of a pixel in geographic units (decimal degrees)

Example Coordinate File:

ulxmap 30.0000000000000000000000000
ulymap 20.0000000000000000000000000
urxmap 50.0000000000000000000000000
urymap 20.0000000000000000000000000
llxmap 30.0000000000000000000000000
llymap 0.0000000000000000000000000
lrxmap 50.0000000000000000000000000
lrymap 0.0000000000000000000000000
xdim 0.0083333333333333285900000
ydim 0.0083333333333333285900000

The Data Descriptor Record (.ddr) - This file has been included to allow the
image to be read directory by EDC's LAS software. To take advantage of this,
the image file extension will have to be renamed from .bil to .img. This file
contains all of the information contained in the other data files.

Example Data Descriptor Record:

IMAGE NAME:af_dem_lks1.bil
NL:4201 NS:1201 NB:1 DTYPE:INTEGER*2
LAST MODIFIED: DATE: TIME: SYSTEM:ieee-std
PROJ. CODE:(0)GEOGRAPHIC Valid:VALID
ZONE CODE:0 Valid:INVALID
DATUM CODE:0 Valid:INVALID
PROJ. PARM: Valid:VALID
A: 0.00000000000000E+00 0.00000000000000E+00 0.00000000000000E+00
B: 0.00000000000000E+00 0.00000000000000E+00 0.00000000000000E+00
C: 0.00000000000000E+00 0.00000000000000E+00 0.00000000000000E+00
D: 0.00000000000000E+00 0.00000000000000E+00 0.00000000000000E+00
E: 0.00000000000000E+00 0.00000000000000E+00 0.00000000000000E+00
CORNER COOR: Valid:VALID
ULcorner:-5.00000000000000E+00 -1.50000000000000E+01
URcorner:-5.00000000000000E+00 -5.00000000000000E+01
LLcorner:-4.00000000000000E+01 -1.50000000000000E+01
LRcorner:-4.00000000000000E+01 -5.00000000000000E+01
PROJ. DIST:8.33333333333333E-03 8.33333333333333E-03 Valid:VALID
PROJ. UNITS: degrees Valid:VALID
INCREMENT:0.00000000000000E+00 0.00000000000000E+00 Valid:INVALID
MASTER COOR:0 0

BAND NO:1

MINIMUM:1.00000000000000E+00 Valid:VALID
MAXIMUM:6.54800000000000E+03 Valid:VALID

DATA SOURCE:
SENSOR TYPE:
CAPT. DIRECTION:
DATE:
TIME:

ACQUISITION
SOURCES

Antarctic Digital Elevation Model (DEM) data are produced from contour and
coastline data supplied with the Antarctic Digital Database (ADD), produced
under the auspices of the Scientific Committee on Antarctic Research (SCAR).
The ADD contours were compiled from source maps at scales ranging from
1:200,000 to 1:5,000,000.

PROCESSING STEPS
DEM GENERATION:

Once the data are pre-processed, they are used as input into the
Australian National University Digital Elevation Model (ANUDEM)
generation program developed by Michael Hutchinson, Centre for
Resources and Environmental Studies, Australian National University.
This program first reads input elevations, windows the data to the
specified map limits, then generates a grid at a 1 km point spacing in
a polar stereographic projection.

Elevation data are generalized by accepting a maximum of 4 data points
per grid cell and discarding any remaining points. Contour data are
generalized by accepting a maximum of one line per grid cell. The
program then employs a multi-grid method that calculates grids at
successively finer resolutions until the specified grid resolution is
achieved. During this process, drainage conditions are imposed to
remove sinks where possible. Values at grid points not occupied by
data points are calculated by Gauss-Seidel iteration with over
relaxation (SOR method) subject to an appropriate roughness penalty
and ordered chain constraints. The ordered chain constraints are
obtained from the stream line, sink point, and contour line data and
through automatic drainage enforcement as calculated by the program.
Starting values for the first coarse grid resolution are calculated
from a least squares plane fit to the data points. Values for each
succeeding grid are linearly interpolated from the preceding grid
(M.F. Hutchinson, unpub. data, 1991).

After DEM generation, the resultant data was transformed into
geographic coordinates using ARC/INFO.

DATA CHARACTERISTICS
SPATIAL RESOLUTION

The Antarctic DEM is distributed in two forms to address the
complications inherent in equiangular point spacing near the poles.

ant_dem_1kmps.bil presents elevation information at a 1 km point
spacing based on a polar stereographic projection.

ant_dem_1kms1.bil, ant_dem_1kms2.bil, ant_dem_1kms3.bil, and
ant_dem_1kms4.bil present the DEM data in geographic (lat/lon)
coordinates, with a point spacing of 30 arc seconds.

The horizontal datum is WGS84. Elevation values are expressed in
meters above mean sea level.

ACCURACY

The absolute accuracy of the ADD vector information is difficult to
assess, as the ADD was produced from a broad variety of cartographic
sources. However, the accuracy of the grid generated from these data
will be no more accurate than this source. The accuracy for the grid
has not been measured or calculated.

DATA AVAILABILITY
PROCEDURES FOR OBTAINING DATA

Haiti, Madagascar and Africa datasets are available through an
Internet anonymous File Transfer Protocol (FTP) account at the EDC (at
no cost).

Orders for tape copies can be placed through the GLIS Inventory
SUMMARY RESULTS screen or by contacting the EROS Data Center,
Customer Services section, at the following address:

Customer Services
EROS Data Center
Mundt Federal Building
Sioux Falls, SD 57198
TEL: (605) 594-6151
FAX: (605) 594-6589

Customer Services can also be contacted for information about DCW DEM
data that are in progress. As additional geographic areas become
available they will be announced in the GLIS News.

PRODUCTS AND SERVICES

DCW DEM data are available from the EROS Data Center on unlabeled
magnetic tape. Africa, North America, Madagascar, and Haiti datasets
can be obtained through anonymous FTP. Instructions for accessing the
anonymous FTP account can be found under Procedures for Obtaining
Data.

APPLICATIONS AND RELATED DATA SETS

Moderate resolution (100 meter to 1 kilometer) topographic data have
applications in many diverse land science fields such as geology and
geophysics, ecology, soil science, botany, and glaciology.
Topographic data are also critical to procedures used for correcting
and/or presenting remotely sensed satellite and other global data.

The elevation data available here are a result of the global 30
arc-second elevation data project being carried out by staff of the
USGS' EROS Data Center (EDC) in Sioux Falls, South Dakota and the
co-located United Nations Environment Program / Global Resource
Information Database office (UNEP/GRID). The broad goal of this
project is the completion of global 1 km elevation data for the land
surface and the systematic extraction of derivative information to
assemble a global data base of topographic elevation, slope, aspect,
hydrologic flow paths, and watersheds. The primary collaborators and
data contributors to date are the USGS, NASA, UNEP/GRID, USAID, DMA,
the Instituto Nacional de Estadistica Geografica e Informatica (INEGI)
of Mexico, and the Geographical Survey Institute of Japan.

Geographic Coverage
 N: -60.0 S: -90.0  E: 180.0  W: -180.0

Data Set Citation
Dataset Originator/Creator: USGS/EROS DATA CENTER
Dataset Title: 30 ARC-SECOND DEM For Antarctica
Online Resource: http://www.grid.unep.ch/data/summary.php?dataid=GNV189&category=lit...


Temporal Coverage
Start Date: 1996-07-17
Stop Date: 1996-07-17


Location Keywords
CONTINENT > ANTARCTICA
GEOGRAPHIC REGION > POLAR


Science Keywords
LAND SURFACE >TOPOGRAPHY >TERRAIN ELEVATION >DEM    [Definition]


ISO Topic Category
ELEVATION


Platform
DEM >Digital Elevation Model    [Information]


Access Constraints
Public


Keywords
ELEVATION
TOPOGRAPHY
DIGITAL ELEVATION MODEL


Data Center
Global Resource Information Database - Nairobi, Division of Early Warning and Assessment, United Nations Environment Programme
Data Center URL: http://gridnairobi.unep.org/
Dataset ID: GNV189

Data Center Personnel
Name: JOHANNES AKIWUMI
Phone: (+254-20) 7624214
Fax: (+254-20) 7624315
Email: Johannes.Akiwumi at unep.org
Contact Address:
Head, Data and Information Management Section
Division of Early Warning and Assessment (DEWA)
United Nations Environment Programme
P. O. Box 30552
City: Nairobi
Postal Code: 00100
Country: Kenya


Personnel
JOHANNES AKIWUMI
Role: TECHNICAL CONTACT
Phone: (+254-20) 7624214
Fax: (+254-20) 7624315
Email: Johannes.Akiwumi at unep.org
Contact Address:
Head, Data and Information Management Section
Division of Early Warning and Assessment (DEWA)
United Nations Environment Programme
P. O. Box 30552
City: Nairobi
Postal Code: 00100
Country: Kenya


Publications/References
Defense Mapping Agency, 1992, Development of the Digital Chart of the World: Washington, D.C., U.S. Government Printing Office.

Environmental Systems Research Institute, 1991, Image Integration ARC/INFO User's Guide: Redlands, California, Environmental Systems Research Institute, Inc.

Hutchinson, M.F., 1988, Calculation of hydrologically sound digital elevation models: Proc. Third Inter. Symp. Spatial Data Handling, Columbus, Ohio, August 17-19.

Hutchinson, M.F., 1989, A new method for gridding elevation and stream line data with automatic removal of pits: J. Hydrol, 106, 211-232 p.

Hutchinson, M.F., 1991, A continental hydrological assessment of a new grid- based digital elevation model of Australia: Hydrological Processes 5, 45-58 p.

Creation and Review Dates
DIF Creation Date: 1996-11-18
Last DIF Revision Date: 2012-06-11

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