Reduced-Resolution Radar Imagery, Digital Elevation Models, and Related GIS Layers for Barrow, Alaska, USA

Summary

This product set contains reduced-resolution Interferometric Synthetic Aperture Radar (IFSAR) imagery and geospatial data for the Barrow Peninsula (155.39 - 157.48°W, 70.86 - 71.47°N), for use in Geographic Information Systems (GIS) and remote sensing software. The primary IFSAR data sets were acquired by Intermap Technologies from 27 to 29 July 2002, and consist of an Orthorectified Radar Imagery (ORRI), a Digital Surface Model (DSM), and a Digital Terrain Model (DTM).

Derived data layers include aspect, shaded relief, and slope-angle grids (floating-point binary format), as well as a vector layer of contour lines (ESRI Shapefile format). Also available are accessory layers compiled from other sources: 1:250,000- and 1:63,360-scale USGS Digital Raster Graphic (DRG) mosaic images (GeoTIFF format); 1:250,000- and 1:63,360-scale USGS quadrangle index maps (ESRI Shapefile format); and a simple polygon layer of the extent of the Barrow Peninsula (ESRI Shapefile format).

The DSM and DTM data sets (20 m resolution) are provided in floating-point binary format with header and projection files. The ORRI mosaic (5 m resolution) is available in GeoTIFF format. FGDC-compliant metadata for all data sets are provided in text, HTML, and XML formats, along with the Intermap License Agreement and product handbook.

The baseline geospatial data support education, outreach, and multi-disciplinary research of environmental change in Barrow, which is an area of focused scientific interest. Data are available via FTP and CD-ROM.

Citing These Data

Manley, W. F., L. R. Lestak, C. E. Tweedie, and J. A. Maslanik. 2005. Reduced-resolution radar imagery, digital elevation models, and related GIS layers for Barrow, Alaska, USA . Boulder, CO: National Snow and Ice Data Center. Digital media and CD-ROM.

Overview Table

Please see the File List and the FGDC metadata for details about specific layers, including data sources, processing, data format, spatial and temporal resolution, extent, projection, and datum.

Category Description
Data format Primary, derived, and accessory data layers are provided in different formats, including floating-point binary, GeoTIFF, and ESRI Shapefiles.
Spatial coverage

Barrow Peninsula extent:
West: 157.476330°W
East: 155.394828°W
North: 71.472777°N
South: 70.862456°N

Temporal coverage and resolution Data extend from 27 to 29 July 2002.
Tools for accessing data These data are easily imported into ArcGIS and image processing software (ENVI, Erdas Imagine, and others).
Grid type and size Refer to the FGDC metadata (accessed from the File List) for details specific to each layer.
File naming convention See File List.
File size See File List.
Parameter(s) Elevation, terrain, radar imagery, aspect, shaded relief, slope, contours
Procedures for obtaining data Data are available via FTP. To request a copy of the CD-ROM, complete the Data Order Form.

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments

Investigator(s) Name and Title

William F. Manley
Institute of Arctic and Alpine Research (INSTAAR)
University of Colorado
Boulder, CO, USA

Leanne Lestak
Cooperative Institute for Research in Environmental Sciences (CIRES)
University of Colorado
Boulder, CO, USA

Craig Tweedie
Arctic Ecology Laboratory
Michigan State University
Lansing, MI, USA

James Maslanik
Cooperative Institute for Research in Environmental Sciences (CIRES)
University of Colorado
Boulder, CO, USA

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org

Acknowledgements

This research was funded by the National Science Foundation Award OPP-0224071, "High-Resolution Imagery and Terrain Model for Collaborative Research of Environmental Change at Barrow, Alaska."

NSIDC Distribution Liability Statement

The National Snow and Ice Data Center (NSIDC) shall not be held liable for improper or incorrect use of the data described and/or contained herein. The information contained in these data is dynamic and may change over time. The data are not better than the original sources from which they were derived. It is the responsibility of the data user to use the data appropriately and consistently within the limitations of geospatial data in general and these data in particular. Any related graphics are intended to aid the data user in acquiring relevant data; it is not appropriate to use the related graphics as data. NSIDC gives no warranty, expressed or implied, as to the accuracy, reliability, or completeness of these data. These data and related graphics are not legal documents and are not intended to be used as such. This disclaimer applies both to individual use of the data and aggregate use with other data.

2. Detailed Data Description

This product set contains reduced-resolution Interferometric Synthetic Aperture Radar (IFSAR) imagery and geospatial data for the Barrow, Alaska, USA region for use in Geographic Information Systems (GIS) and remote sensing software packages. The baseline geospatial data support education, outreach, and multi-disciplinary research of environmental change in Barrow, an area of focused scientific interest. The data are provided on CD and by FTP. High-resolution versions of the data sets are available to investigators funded by the National Science Foundation (NSF).

The primary IFSAR data sets were acquired by Intermap Technologies from 27 to 29 July 2002, and consist of Orthorectified Radar Imagery (ORRI), a Digital Surface Model (DSM), and a Digital Terrain Model (DTM). The ORRI depicts the ground surface as illuminated by airborne radar, and is useful for visualization, mapping, georectification, and a variety of analyses. The DSM is a "first-surface" reflectance model of elevation, including vegetation, buildings, and other structures. The DTM is a filtered model to better represent ground elevation, and is useful for visualization, orthorectification, and environmental analyses.

Value-added processing helped avoid redundant effort or confusion, and produced a suite of complete and consistent data. The DSM, DTM, and ORRI went through rigorous quality reviews before final acceptance of the data from Intermap Technologies. To make the primary data sets more usable, 26 original data tiles were converted to data mosaics at full 5 m resolution with a common projection (UTM Zone 4) for the spatial extent of the "Barrow Peninsula" (155.39 to 157.48°W, 70.86 to 71.47°N). These 5 m mosaics were resampled to 20 m resolution for a reduced-resolution version, available free of charge with a public-use license. The DSM and DTM mosaics are available as floating-point binary files. An ORRI mosaic, at reduced resolution (5 m), is provided as a contrast-enhanced GeoTIFF file. Also included are the Intermap License Agreement and product handbook.

Processing included the creation of derived GIS layers: aspect, shaded relief, and slope-angle grids (floating-point binary), as well as a vector layer of contour lines (ESRI Shapefile format). Also available are accessory layers compiled from other sources: 1:250,000- and 1:63,360-scale USGS Digital Raster Graphic (DRG) mosaic images (GeoTIFF format); 1:250,000- and 1:63,360-scale USGS quadrangle index maps (ESRI Shapefile format); and a simple polygon layer of the extent of the Barrow Peninsula (ESRI Shapefile format).

Finally, detailed documentation was created for all of the data layers. Federal Geographic Data Committee (FGDC)-compliant metadata are provided in text, HTML, and XML formats. Please read the FGDC metadata and view the thumbnail images (accessed from the File List) for a variety of details specific to each layer or image.

Primary Data Layers

Digital Surface Model (DSM)
DSM sample The DSM is a grid of elevation measurements derived from the return signals received by two radar antennas on the aircraft. The signals bounce off the first surface they strike, making the DSM a representation of any object large enough to be resolved, including buildings, vegetation and roads, as well as natural terrain features.
 
Digital Terrain Model (DTM)
DSM sample The DTM is a custom "bald-earth" model that references the elevation measurements of the bare terrain. It is better suited for derived layers such as slope angle, aspect, and contours. DTM values are a result of a custom process developed for the low coastal plain of Alaska's North Slope. A repeated median filter removed most structures, as well as high-frequency noise. The DTM is well-suited for most applications of elevation analysis.
 
Orthorectified Radar Imagery (ORRI)
DSM sample The ORRI is a grayscale image of the first reflective surface illuminated by the radar; it was corrected to remove geometrical distortions. This radar-derived product reveals Earth surface features that are not easily identifiable with aerial photography. Furthermore, the ORRI is well suited as a base layer for georectification of aerial photography and other imagery.

Derived Data Layers

The following value-added layers are provided with the same projection, datum, and spatial extent as the DSM, DTM, and ORRI. Please consult the metadata (accessed from the File List) provided with each layer for further details.

Aspect
Aspect
Slope
Slope
Shaded relief
Shaded relief
Contours
Contours

Accessory Data Layers

1:250,000 DRG
mosaicked 1:250,000 scale USGS Digital Raster Graphic (DRG)
1:63,360 DRG
mosaicked 1:63,360 scale USGS DRG
1:250,000 index map
1:250,000 scale USGS quadrangle boundaries
1:63,360 index map
1:63,360 scale USGS quadrangle boundaries
Barrow Peninsula extent
Barrow Peninsula extent boundary

Format

The primary, derived, and accessory data layers are provided in a variety of standardized data formats, including floating-point binary, GeoTIFF, and ESRI Shapefiles. The layers vary in terms of grid cell resolution and dimensions. For example, the DSM mosaic for the Barrow Peninsula is available in floating-point binary format, has grid cell spacing of 20 m, and dimensions of 3,255 rows by 3,615 columns. Please see the FGDC metadata (accessed from the File List) for details specific to each layer. To read the floating-point DSM and DTM into an image processing program, refer to the associated header files (.hdr). To import the floating-point DSM and DTM into ArcGIS, use the FLOATGRID command. Or, in ArcToolbox choose Conversion Tools / Import to Raster / Floating Point Data to Grid.

File and Directory Structure

File names for GIS layers of the Barrow Peninsula begin with "bp." Names for most of the raster layers also include a number indicating horizontal resolution. For example, "bp20_dsm" is the reduced-resolution version of the DSM with 20 m grid-cell spacing.

Follow the links in the tables below to view FGDC metadata, which provide details about specific data layers, including data sources, processing, data format, spatial and temporal resolution, extent, projection, and datum.

.html, .xml, .txt: Federal Geographic Data Committee (FGDC) metadata
.hdr: ArcInfo header file
.prj: ArcInfo projection file
.tfw: GeoTIFF world file
.dbf, .prj, .sbn, .sbx, .shx: ESRI Shapefiles
.flt: 32-bit IEEE signed floating-point binary file

File List
Approximate
File Size
File Names Description Format Accompanying Metadata
3 KB 0README_CD.txt Readme File Text  
1 KB readme_nsidc.txt Readme File Text  
82 KB EULA_Resampled_Unrestricted.pdf Intermap License Agreement PDF  
3 MB gt_product_handbook_v2_3.pdf Intermap Product Handbook PDF  
180 MB bp05_orri_mosaic.aux
bp05_orri_mosaic.tif
bp05_orri_mosaic.tfw

ORRI mosaic raster

browse image

GeoTIFF .html, .txt, .xml
45 MB bp20_aspect.flt
bp20_aspect.hdr
bp20_aspect.prj

Reduced-resolution (20 m) aspect raster

browse image

Floating-point binary .html, .txt, .xml
47 MB bp20_contours.shp
bp20_contours.dbf
bp20_contours.prj
bp20_contours.shx

Reduced-Resolution (20 m) contours

browse image

ESRI Shapefile .html, .txt, .xml
45 MB bp20_dsm.flt
bp20_dsm.hdr
bp20_dsm.prj

Reduced-resolution (20 m) DSM raster

browse image

Floating-point binary .html, .txt, .xml
45 MB bp20_dtm.flt
bp20_dtm.hdr
bp20_dtm.prj

Reduced-resolution (20 m) DTM raster

browse image

Floating-point binary .html, .txt, .xml
45 MB bp20_shaded.flt
bp20_shaded.hdr
bp20_shaded.prj

Reduced-resolution (20 m) shaded relief raster

browse image

Floating-point binary .html, .txt, .xml
45 MB bp20_slope.flt
bp20_slope.hdr
bp20_slope.prj

Reduced-resolution (20 m) slope raster

browse image

Floating-point binary

.html, .txt, .xml
21 MB bp_drg_250.tif
bp_drg_250.tfw

1:250,000 scale USGS Digital Raster Graphic (DRG)

browse image

GeoTIFF .html, .txt, .xml

325 MB
uncompressed

bp_drg_63.tif
bp_drg_63.tfw

1:63,360 scale USGS DRG

browse image

GeoTIFF .html, .txt, .xml
1 MB bp_extent.dbf
bp_extent.prj
bp_extent.sbn
bp_extent.sbx
bp_extent.shp
bp_extent.shx

Barrow Peninsula extent boundary

browse image

ESRI Shapefile .html, .txt, .xml
508 KB bp_itmquad.dbf
bp_itmquad.prj
bp_itmquad.sbn
bp_itmquad.sbx
bp_itmquad.shp
bp_itmquad.shx

1:63,360 scale USGS quadrangle boundaries

browse image

ESRI Shapefile .html, .txt, .xml
625 KB bp_qmquad.dbf
bp_qmquad.prj
bp_qmquad.sbn
bp_qmquad.sbx
bp_qmquad.shp
bp_qmquad.shx

1:250,000 scale USGS quadrangle boundaries

browse image

ESRI Shapefile .html, .txt, .xml
181 KB bp_quarter_quads.dbf
bp_quarter_quads.prj
bp_quarter_quads.sbn
bp_quarter_quads.sbx
bp_quarter_quads.shp
bp_quarter_quads.shx

Quarter quadrangle tile boundary index map

browse image

ESRI Shapefile .html, .txt, .xml
390 MB bt_extent.dbf
bt_extent.prj
bt_extent.shp
bt_extent.shx

Barrow Peninsula extent boundary

browse image

ESRI Shapefile .html, .txt, .xml

Spatial Coverage

Spatial extent of the Barrow Peninsula layers:

West: 157.476330°W
East: 155.394828°W
North: 71.472777°N
South: 70.862456°N

Spatial Coverage Map

The following map displays the spatial extent of the Barrow Peninsula (red lines) and Barrow Triangle (purple lines) data sets. Click the thumbnail for a larger image.

Coverage Map

Projection

The map projection for the Barrow Peninsula data sets is Universal Transverse Mercator (UTM), Zone 4. Horizontal datum is the North American Datum of 1983 (NAD83).

Temporal Coverage

Intermap Technologies' STAR-3i airborne radar system collected data from 27 to 29 July 2002.

Parameter or Variable

Unit of Measurement

Pixel values in the DSM and DTM represent values above mean sea level (in meters). Pixels in the ORRI mosaics are greyscale values that represent magnitude of radar signal return.

Error Sources

Several potential sources of error exist in the DSM and DTM, as well as other layers. For more information, refer to the FGDC metadata (accessed from the File List).

25 April 2004
NSIDC discovered the file "bp20_dsm.hdr" contained an unnecessary reference to ENVI software. The correct header information should be:

ncols 3615
nrows 3255
xllcorner 555660
yllcorner 7865740
cellsize 20
NODATA_value -9999
byteorder LSBFIRST

This file was replaced on the FTP site and CD-ROM (labeled "Version 1.1").

Quality Assessment

Quality checks were performed throughout all processing steps. Minimum and maximum domain values were checked for each tile, for merged and mosaicked products. Map extents of separate tiles are correct. Overlaps between tiles are seamless and contain identical values. Value-added layers and their ranges were quality checked; these value-added layers were also used to quality check the values in the DSM.

The vertical accuracy of DSMs and DTMs is approximately ± 1.0 m or better root-mean-square-error (RMSE). Horizontal accuracy is ± 2.5 m or better RMSE for slopes less than 20°. Horizontal accuracy of ORRI data is ± 1.25 m or better RMSE for slopes less than 20°. These accuracy statements depend on the sensor's view of the ground, and are applicable to the height of the first surface return. These statements also assume the surface is devoid of vegetation or continuous roof coverage in urban areas (Intermap 2002).

Accuracy statements are based on areas of moderate terrain. Diminished accuracies are to be expected in areas of extreme terrain and dense vegetation. The DSM and DTM contain some small (30 to 50 cm high) ripples or "corn rows." The Intermap data collection systems are very accurately calibrated to control the constant differential phase error between the antennae. The calibration ensures that data are within specification; however, on flat terrain, very low-level artifacts are present from uncompensated differential phase errors. Very small periodic DEM ripples in the range dimension occurred at a consistent location in range and are continuous along the strip. High-frequency variation (speckle) exists in both the imagery and terrain data sets. The high-frequency variation in the DEM is a product of the signal-to-noise ratio that decreases from the near to far range across the track; therefore, the noise increases with the distance from the antenna. The difference in noise between the near and far range of the strip can sometimes be seen at the seam where DEMs from two strips are mosaicked together.

3. Data Access and Tools

Data Access

Data are available via FTP. To request a copy of the CD-ROM, complete the Data Order Form.

Volume

The entire data set is approximately 500 MB.

Software and Tools

NSIDC does not provide any software to read these data, which are easily imported into ArcGIS and image processing software.

Related Data Collections

4. Data Acquisition and Processing

Theory of Measurements

The DSM, DTM, and ORRI are derived from airborne Interferometric Synthetic Aperture Radar (IFSAR). Interferometry involves detecting the radar return signal using antennas at two different locations. With an interferometric radar, the patterns of electromagnetic radiation emanating from the same point on the ground strike each antenna independently because of their different ranges. These waves are out of phase, meaning they do not always overlap each other. This phase difference result, and the geometry formed by the separation of antennas, provide all the information required to derive the height and corresponding geographic position of targets that interact with the transmitted energy (Intermap 2002).

Sensor or Instrument Description

IFSAR data were acquired from Intermap Technologies' STAR-3i airborne radar system aboard a Learjet 36A, 31,000 ft above ground level. The system transmits a radar pulse 2,200 times per second at a peak power of 8 W. Bandwidth is 135 MHz, digitization rate of the return signal is 300 million times per second, and information is recorded at 90 MB per second. The radar is mounted on a pedestal that rotates to allow the crew to collect data from either side of the aircraft, using two parallel antennas separated by 1 m. Each terrain height calculation represents the average height within the 1.25 m resolution cell (Tennant, Coyne, DeCol 2003). Acquired data are "interfered" by a digital correlation process to extract terrain height data and geometrically correct radar images. Areas of missing data are interpolated using continuous curvature spline over non-data areas. Most of these instances are due to radar shadow and layover due to steep terrain. The system's accuracy was independently validated by the U.S. Army Topographic Engineering Center, the Institute of Navigation, Stuttgart University, and by NASA.

The STAR-3i system was developed by the Environmental Research Institute of Michigan (ERIM) under contract to the U.S. Defense Advanced Research Projects Agency (DARPA).

Data Acquisition Methods

Raw radar and navigation information are combined to produce flight strip information referenced in a radar-specific coordinate system, which are then subject to quality control (QC). Once they pass QC, the strips are transformed to the desired map projection, merged into map sheet products for elevation, radiometrically balanced, and mosaicked into map sheets (Tennant, Coyne, DeCol 2003).

Processing Steps

IFSAR data for the Barrow region were originally delivered by Intermap Technologies as 26 tiles of data split across UTM Zones 4 and 5. Manley et al. imported the tiles into ArcInfo, merged tiles within each zone, and projected Zone 5 to Zone 4 to produce a mosaic across both zones. Data were then clipped by a Barrow Peninsula extent and a Barrow Triangle extent. (See High-Resolution Radar Imagery, Digital Elevation Models, and Related GIS Layers for Barrow, Alaska, USA for data layers subsetted to the extent of the Barrow Triangle.) These mosaics were then regridded to 20 m, to make a free, reduced-resolution version available to the general public.

5. References and Related Publications

Intermap Technologies, Inc. 2002. GLOBAL terrain product handbook and quick start guide. Englewood, CO, USA: Intermap Technologies Inc.

Tennant, J.K., T. Coyne, and E. DeCol. 2003. Star-3i interferometric synthetic aperture radar (IFSAR): more lessons learned on the road to commercialization. Calgary, Alberta: Intermap Technologies Corp.

6. Document Information

List of Acronyms

The following acronyms are used in this document:

ARCSS: Arctic System Science
BIL: Band interleaved by line
CIRES: Cooperative Institute for Research in Environmental Sciences
DARPA: Defense Advanced Research Projects Agency
DEM: Digital Elevation Model
DRG: Digital Raster Graphic
DSM: Digital Surface Model
DTM: Digital Terrain Model
ERIM: Environmental Research Institute of Michigan
ESRI: Environmental Systems Research Institute
IFSAR: Interferometric Synthetic Aperture Radar
GIS: Geographic Information Systems
NAD: North American Datum
NSF: National Science Foundation
NSIDC: National Snow and Ice Data Center
ORRI: Orthorectified Radar Imagery
QC: Quality Control
RMSE: Root-mean-square error
USGS: United States Geological Survey
UTM: Universal Transverse Mercator

Document Creation Date

February 2005

Document Revision Date

February 2005

Document Review Date

February 2005

Document URL

http://nsidc.org/data/docs/arcss/arcss303/index.html