30 arc-second DEM for Europe
Entry ID:
GNVd0190_104
|
[
Update this Record
]
|
Updating this record requires registration.
|
Summary
Abstract:
PLEASE NOTE: This is a preliminary release of the European 30 arc-second DEM. Constructive comments from users of this data set are greatly appreciated. Please contact Kris Verdin (kverdin@edcserver1.cr.usgs.gov) or Sue Jenson (jenson@edcserver1.cr.usgs.gov) with your comments. Data Set Assembly A Digital Elevation Model (DEM) consists of a sampled array of elevations for ground positions that ... are normally spaced at regular
intervals. The EROS Data Center's (EDC) 30 arc-second DEM project
includes generation of 30 arc-second DEM data for the entire world.
These data are being made available to the public via anonymous ftp as
they become available. As major geographic regions are completed, the
data, along with various derivative data sets, will be published on
CD-ROM. As of September 1995, Europe, North America, Africa, Japan,
Madagascar and Haiti are complete and available for distribution. The
South American data set is under development, as are Asia and
Australia.
The European 30 arc-second DEM was compiled from varied data sources.
The primary source was a generalization of the Level 1 Digital Terrain
Elevation Data. Digital Terrain Elevation Data (DTED) is a 1 degree
by 1 degree dataset produced by the US Defense Mapping Agency (DMA)
that contains digital data in the form of a uniform matrix of terrain
elevation values for most parts of the world. It was originally
designed to provide basic quantitative data for military training,
planning and operating systems that require terrain elevation, slope
and related information. This includes applications such as modeling
the influence of terrain on radar line-of-sight, automatic height
determination, terrain modeling etc.
The EROS Data Center's Digital Elevation Modeling project, that
includes generation of 30 arc second data for the entire world,
employed the DTED-Level 1 data in developing a 30 arc second DEM of
Europe. The DTED data cover over 99% of the landmass of Europe. The
elevation data for the small areas of Europe which are not covered by
the DTED data were developed using the 1:1,000,000 scale Digital Chart
of the World (DCW) mapping. The point and contour hypsography
coverages were processed into a 30 arc-second DEM using the ANUDEM
gridding software. This software utilized the DCW hydrography
information along with the hypsography to generate a hydrologically
realistic DEM. This technique was used to produce the 30 arc-second
DEM in all areas not covered by existing, distributable DEMs. The
data generated in this fashion were merged with the existing resampled
data using various mosaicing techniques to minimize the
discontinuities between the two data sources.
Spatial extent of coverage
The spatial extent of Europe follows the definition of National
Geographic:
"A commonly accepted division between Asia and Europe is formed by the
Ural Mountains, Ural River, Caspian Sea, Caucasus Mountains, and the
Black Sea with its outlets, the Bosporus and Dardanelles." (National
Geographic Magazine, December, 1992). The European 30 arc-second DEM
extends slightly beyond this division with longitudinal extent of 25W
to 70E and a latitudinal extent of 35N to 85N.
Data sources and characteristics
DTED-1 has been derived from a number of cartographic and photographic
sources, and by utilizing various techniques. Level 1 within DTED
refers to the specific spatial resolution model used, which in this
case, posts every 3 arc second in the original data.
DTED-1 is set to the Geographic Coordinate Reference System, and
the following datum specifications:
Horizontal: World Geodetic System (WGS 84)
Vertical : Mean Sea Level (MSL)
The standard file size is a 1 degree by 1 degree geographic cell
referenced by its south-west corner coordinates. Each of the
elevation data records contain 1201 elevation values in meters along a
single meridian, and a cell can have 201 to 1201 elevation data
records depending on the latitudinal location. The spacing of
elevations is according to the following:
Latitude Spacing - Latitude/Longitude
0 - 50 N-S 3 by 3 arc seconds
50 - 70 N-S 3 by 6 arc seconds
70 - 75 N-S 3 by 9 arc seconds
75 - 80 N-S 3 by 12 arc seconds
80 - 90 N-S 3 by 18 arc seconds
The accuracy objectives for DTED-1 according to the DMA Product
Specifications are as follows:
Absolute Horizontal 130 meters at 90% circular error
Absolute Vertical +/- 30 meters at 90% linear error
Mechanics of the DEM generation
The original 3 arc second DTED-1 data for Europe exists in a dozen
Compact Discs (CD-ROM) that use the standard volume and file structure
- ISO 9660. This data was converted to a Grid format using Arc/Info's
Grid module, which produced a dozen grids covering Europe. These full
resolution 3 arc second grids were resampled to 30 arc second using
Grid's "aggregate" function that generates a reduced resolution
version of a grid:
Grid: aggregate (, , {aggregation_type},
{expand | truncate}, {data | nodata})
The cell size of 3.000 in the original grids were aggregated using a
cell factor of 10 and median as the aggregation type. To deal with
the boundaries of the input grid when its rows and/or columns are not
a multiple of the cell factor, the "truncate" option was used. This
option reduces the number of rows and/or columns in the output grid by
one. Doing so truncates the remaining cells on the bottom and/or
right boundaries of the input grid thus making the number of rows
and/or columns in the input grid a multiple of the cell factor. The
resulting output grid's spatial extent can thus be smaller than the
input grid. The "nodata" option used specifies that if any cell that
falls within the spatial extent of a larger cell on the output grid
has a value of nodata, then the value for that output cell location
will be nodata.
Data Distribution
The European 30 arc-second DEM covers the European landmass from 25W
to 70E longitude and 35N to 85N latitude. The raster image contains
representative elevation values for each pixel in meters above MSL.
In order to facilitate distribution of the data, the DEM has been
divided into two equal pieces as follows:
EXTENT
DEM Name Longitudinal Latitudinal
eur_30_dem1 25W - 22.5E 35N - 85N
eur_30_dem2 22.5E - 70E 35N - 85N
Data are distributed as compressed BIL images, 16-bit straight raster
image files in a latitude/longitude coordinate system. The image
files were compressed using the GNU 'gzip' utility and can be
identified by the .bil.gz extensions. These files must be
uncompressed before use. They can be uncompressed with the gzip
utilities or if you do not have access to gzip, the FTP server can
uncompress the files as you retrieve them. 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
"eur_30_dem1.bil.gz" without compression just use "get
eur_30_dem1.bil". Please note that the uncompressed files are
typically five times larger than the compressed versions and therefore
will take five times longer to transmit. If you would like to obtain
the gzip program, it is available via anonymous FTP at the following
sites:
prep.ai.mit.edu:/pub/gnu
wuarchive.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 DEM Name makes up the prefix of each file. The three
digit suffix varies depending on the file type. The formats of the
ancillary files are 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 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 (1)
nbits: number of bits per pixel (16)
bandrowbytes: number of bytes per band per row (twice the number of columns)
totalrowbytes: total number of bytes of data per row (twice the number
of columns)
bandgapbytes the number of bytes between bands in a BSQ format image (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 6000
NCOLS 5700
NBANDS 1
NBITS 16
BANDROWBYTES 11400
TOTALROWBYTES 11400
BANDGAPBYTES 0
NODATA -9999
ULXMAP -24.99583333333333
ULYMAP 84.99583333333333
XDIM 0.0083333333333
YDIM 0.0083333333333
World File (.blw)
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 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):
Example World file: Description
0.0083333333333333 x dimension of a pixel (decimal degrees)
0.00000000000000 rotation term (will always be zero)
0.00000000000000 rotation term (will always be zero)
-0.0083333333333333 negative y-dimension of a pixel (in
decimal degrees)
-24.995833333333333 longitude of the center of the upper-left
pixel
84.995833333333333 latitude of the center of the upper-left
pixel
The Statistics File (.stx)
The statistics file contains the band number, the minimum pixel value
(elevation expressed in meters above mean sea level), the maximum
pixel value, the mean, and the standard deviation.
Example Statistics File:
1 -9999 4536 -7458.3 4475.4
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 -24.99583333333333333
ulymap 84.99583333333333333
urxmap 22.49583333333333333
urymap 84.99583333333333333
llxmap -24.99583333333333333
llymap 35.00416666666666666
lrxmap 22.49583333333333333
lrymap 35.00416666666666666
xdim 0.00833333333333333
ydim 0.00833333333333333
The Data Descriptor Record (.ddr)
This file has been included to allow the image to be read directly 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
the information contained in the other ancillary data files.
Example Data Descriptor Record:
IMAGE NAME: eur.30.dem1;ddr
NL:6000 NS:5700 NB:1 DTYPE:INTEGER*2
LAST MODIFIED: DATE:22-Sep-95 TIME:1608:37 SYSTEM:ieee-std
PROJ. CODE:(0)GEOGRAPHIC Valid:VALID
ZONE CODE:62 Valid:VALID
DATUM CODE:8 Valid:VALID
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:8.49958333333333E+01 -2.49958333333333E+01
URcorner:8.49958333333333E+01 2.24958333333143E+01
LLcorner:3.50041666666867E+01 -2.49958333333333E+01
LRcorner:3.50041666666867E+01 2.24958333333143E+01
PROJ. DIST:8.33333333333000E-03 8.33333333333000E-03 Valid:VALID
PROJ. UNITS:seconds Valid:VALID
INCREMENT:0.00000000000000E+00 0.00000000000000E+00 Valid:VALID
MASTER COOR:0 0
BAND NO:1
MINIMUM:0.00000000000000E+00 Valid:INVALID
MAXIMUM:0.00000000000000E+00 Valid:INVALID
DATA SOURCE:
SENSOR TYPE:
CAPT. DIRECTION:
DATE:
TIME:
Tape Organization
Along with access via ftp transfer, customers can receive these data
sets through a tape order. If the data were obtained through a tape
order, this README.txt file will be the first record on the tape,
followed by the five ancillary files and image. Each ancillary file
contains one record, while for the image, each row of data is one
record long.
The file list for the tape is:
README.txt File: 1 Record: 1 Record Size in Bytes: 22222
eur_30_dem1.hdr 2 2 327
.blw 3 3 222
.stx 4 4 28
.tik 5 5 390
.ddr 6 6 1851
eur_30_dem1.bil 7 7 - 6006 11400
eur_30_dem2.hdr 8 6007 355
.blw 9 6008 222
.stx 10 6009 28
.tik 11 6010 390
.ddr 12 6011 1849
eur_30_dem2.bil 13 6012 - 12011 11400
DCW Gridding Techniques
For the 1 percent of the European landmass lacking DTED data, the
ANUDEM software was used to grid a DEM from the 1:1,000,000 scale DCW
data set.
The map source for the DCW database is the U.S. Defense Mapping Agency
(DMA)'s Operational Navigation Chart (ONC) series. This is the
largest- scale map series that provides consistent, continuous global
coverage of essential basemap features.
A brief description of the techniques used to produce a DEM from the
DCW data set is included here.
Drainage Orientation: Initially, DCW files are stored as vector
contours (hypsography) and hydrology. Using automated stream
orientation procedures, contour line and point data are compared to
the hydrology network to determine drainage direction. Drainage lines
are oriented in the direction of flow, so that they are ordered from
the highest point to the lowest. After the stream orientation process
is complete, the resulting output is verified and edited to ensure
that all streams are represented as flowing downhill.
DEM Generation: Once 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
30-arc-second intervals. Elevation data are generalized by accepting
a maximum of 4 data points per grid cell and discarding any remaining
points. Contour and hydrography line 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).
Data Characteristics
Spatial Resolution
Spacing of the elevations along and between each sample is
30-arc-seconds (approximately 1 km). The horizontal datum is WGS84.
Elevation values are expressed in meters above mean sea level.
Accuracy
The absolute accuracy of the DCW vector information is 2000 meters
circular error (horizontal) and + or - 650 meters linear error
(vertical) at 90-percent confidence as defined by the Defense Mapping
Agency (DMA). 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
30 arc-second data sets for Europe, North America, Africa, Japan,
Madagascar and Haiti are available through an Internet anonymous File
Transfer Protocol (FTP) account at the EDC (at no cost).
To access this account:
1. FTP to 152.61.128.6 (edcftp.cr.usgs.gov)
2. Enter "anonymous" at the Name prompt.
3. Enter your email address at the Password prompt.
4. Change (cd) to the "pub/data/30ASDCWDEM" subdirectory.
5. The files are located under the subdirectories:
EUROPE
NORTH_AMERICA
AFRICA
HAITI
JAPAN
MADAGASCAR
6. Files are named after the image with the following extensions:
*.bil.gz = compressed image file
*.blw = world file
*.hdr = header file
*.stx = statistics file
*.tik = coordinate file
*.ddr = data descriptor record
7. Enter "binary" to set the transfer type
8. Use get or mget to retrieve the desired files.
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
30 arc-second DEM data are available from the EROS Data Center on
unlabeled magnetic tape. European, North America, Africa, Madagascar,
Japan 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 30 arc-second DEM data, produced for use in conducting large-area
studies, have been generated at a resolution which is compatible with
the Advanced Very High Resolution Radiometer (AVHRR) sensor.
References
Defense Mapping Agency, Digitizing the Future, DMA Stock
No. DDIPDIGITALPAC
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.
Attached Raster(s):
Member_ID: 1
Raster Name: WESTERN HALF (35N-85N 25W-22.5E) OF COMPLETE DATA FILE
Raster Projection: GEOGRAPHIC
Raster Resolution: 92
Number of Rows: 6000
Number of Columns: 5700
Number of Bits: 16
Raster
30 ARC-SECOND DEM DATA ARE ALSO AVAILABLE FROM THE USGS/EROS DATA
Attached Raster(s):
Member_ID: 2
Raster Name: EASTERN HALF (35N-85N 22.5E-70E) OF COMPLETE DATA FILE
Raster Projection: GEOGRAPHIC
Raster Resolution: 92
Number of Rows: 6000
Number of Columns: 5700
Number of Bits: 16
Raster
30 ARC-SECOND DEM DATA ARE ALSO AVAILABLE FROM THE USGS/EROS DATA 
Geographic Coverage
(Click for Interactive Map)
Spatial coordinates
| |
N: 85.0
|
|
S: 35.0
|
|
E: 22.0
|
|
W: -25.0
|
Temporal Coverage
Start Date:
1995-09-22
Stop Date:
1995-09-22
Access Constraints
Public
Personnel
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
Creation and Review Dates
DIF Creation Date:
1996-11-18
Last DIF Revision Date:
2012-06-11
|
[
Update this Record
]
|
Updating this record requires registration.
|
|
