This data set contains gridded Digital Elevation Models (DEM) and orthorectified images of Greenland and Antarctica derived from Digital Mapping System (DMS) and Airborne Topographic Mapper (ATM) instrumentation. The data were collected as part of Operation IceBridge funded aircraft survey campaigns.
We kindly request that you cite the use of this data set in a publication using the following citation. For more information, see our Use and Copyright Web page.
Dotson, Ryan C., and John Arvesen. 2014. IceBridge DMS L3 Photogrammetric DEM, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://nsidc.org/data/iodms3.html.
NASA DC-8, NASA P-3B
40 cm resolution gridded DEMs
18 March 2011 to present
Digital Elevation Model (DEM)
GeoTIFF floating point
Ryan C. Dotson
Fireball International Services Corp.
Reno, NV 89519
John C. Arvesen
Cirrus Digital Systems
Tiburon, CA 94920
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
NASA Contract NNH11CC78C. We would like to thank Pete M. Noles, Fireball International Services Corporation for his dedication and many, many long hours processing and verifying these data sets. We would also like to thank the entire DMS instrument group at NASA Ames, and specifically Rose Dominguez, for her support and assistance gathering the DMS raw metadata and her cooperation in modifying DMS operations to help improve the quality of these data sets.
The DEMs are provided as 40 cm resolution gridded, uncompressed 32-bit floating point GeoTIFF files. For a few 23 March 2011 lines, a 20 cm grid was used because of a lower flight altitude.
NOTE: Currently, the TIFF Sample Format tag is not embedded in the images. This results in client programs either auto-detecting the pixel format, or assuming a default. It has been discovered that some programs appear to assume a 32 bit unsigned integer format, while other programs auto-detect the correct 32 bit floating point. In the near future, TIFF headers will be updated to include the TIFF Sample Format tag indicating 32 bit floating point.
Orthorectified color images are provided as 10 to 20 cm gridded compressed 8-bit RGB GeoJPEG files.
XML files contain file level metadata and location, platform, and campaign information.
Data are available on the FTP site in the ftp://n5eil01u.ecs.nsidc.org/SAN2/ICEBRIDGE/IODMS3.001/ directory. Within this directory, the folders are organized by date, for example /2011.03.18/ to /2012.10.12/. Folders contain GeoTIFF, GeoJPG and XML files.
The files are named using the conventions shown below. File name variables are described in Table 1:
Example for a single DMS frame:
|IODMS3||Short name for IceBridge DMS L3 Photogrammetric DEM|
|YYYY||Four-digit year of survey|
|MM||Two-digit month of survey|
|DD||Two-digit day of survey|
|HH||Hour (00 - 23)|
|XX||Hundredths of Second|
|NNNNN||Sequence number from DMS camera|
|TYP||File content type.
DEM: gridded elevation data
RGB: orthorectified visible imagery
.tif = GeoTIFF file
.tfw = TIFF world file
.jpg = JPEG image file
.jgw = JPEG world file
GeoTIFF DEM files range from approximately 4 MB to 8 MB each.
JPEG image files range from approximately 2 MB to 10 MB each.
The entire data set is approximately 9.2 GB.
Spatial coverage for the IceBridge DMS L3 Photogrammetric DEM campaigns include the Arctic and Antarctica from the 2011 to 2013 campaigns.
Arctic / Greenland:
Southernmost Latitude: 60° N
Northernmost Latitude: 90° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Southernmost Latitude: 90°S
Northernmost Latitude: 60°S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Resolution and coverage of DEMs and orthorectified images depends on the flight elevation and source raw image resolution.
The DEMs are 40 cm resolution grids. For a few 23 March 2011 lines, a 20 cm grid was used because of a lower flight altitude.
Orthorectified images are 10 to 20 cm. For a few lines, the resolution is 5 cm, but in general it is 10 cm for Sea Ice flights.
Polar Stereographic North Pole, WGS-84
Polar Stereographic South Pole, WGS-84
These data were collected from 18 March 2011 to the present as part of NASA Operation IceBridge funded campaigns.
IceBridge campaigns are conducted on an annual repeating basis. Arctic and Greenland campaigns are conducted during March, April, and May, and Antarctic campaigns are conducted during October and November.
The IceBridge DMS L3 Photogrammetric DEMs are GeoTIFF imagery, in meters and above the WGS-84 ellipsoid.
The figures below display the IODMS3_20130410_14474149_06610_DEM.tif GeoTIFF DEM file, and the IODMS3_20130410_14474149_06610_RGB.jpg JPEG RGB file.
Figure 1. GeoTIFF DEM File.
Figure 2. Orthorectified JPEG RGB image.
The listing below shows the information embedded in the GeoTIFF DEM image file in Figure 1. GeoTIFF file information can be displayed using tools such as gdalinfo from the Geospatial Data Abstraction Library (GDAL). Visit the GDAL Web site for more information.
gdalinfo output:Driver: GTiff/GeoTIFF
The IODMS3_20130410_14474149_06610_DEM.tfw TIFF World file contains the following:
Data are available via FTP.
Software that recognizes the GeoTIFF file format is recommended for these images. See libGeoTIFF.
Along with coordinate and projection information, additional metadata is embedded in the GeoTIFF files. NSIDC provides a MATLAB GeoTIFF reader that reads time and position from the GeoTIFF data files. The additional fields can be extracted using the gdalinfo command line utility available from the Geospatial Data Abstraction Library (GDAL). Visit the GDAL Web site for more information.
The DMS DEM production process consists of several steps and uses a combination of commercial and custom developed software. Due to limitations of the DMS camera and limitations of the IceBridge flight plans, the photogrammetric DEMs were adjusted to an external control data set. We used IceBridge ATM L1B Elevation and Return Strength QFIT and HDF5 data for this purpose.
The DEMs are first generated by purely photogrammetric techniques using key point matching, bundle adjustment, and dense stereo depth map generation. Agisoft PhotoscanTM is used to do this processing. The result of the Agisoft PhotoscanTM processing is a depth map at a 1:4 resolution ratio from the original imagery.
A rigid Helmert transformation (7 parameters: 1 scale, 3 rotational, 3 translational) is then computed for each depth map to match the ATM point cloud. After alignment, the depth map is projected to a polar stereographic projection and the final DEM and orthorectified images are produced.A quality review is performed on the final frames to identify processing failures.
The altimetry measurements are computed by standard photogrammetric processing techniques with some necessary changes based on the DMS sensor and flight profiles used. The internal algorithmic details used by the Photoscan software package are considered proprietary and are not published by Agisoft. At a high level, the Photoscan processing steps consist of:
Two fundamental challenges with the DMS raw imagery required modifications to this typical DEM generation workflow:
As a result of these limitations, raw output DEMs from the Photoscan software package have vertical and horizontal errors on the order of tens to hundreds of centimeters. In most cases, there are significant "tilts" in the output DEM surfaces which cannot be calibrated out due to the lack of adjacent flight lines.
Thus, a correction/calibration process is used to compute and apply a rigid 3D transformation to correct the depth maps prior to generating the final DEMs. The process is based on minimizing the difference between the DEM and the ATM LIDAR point cloud measurements on a per-frame basis.
The resulting singe-frame DEMs have a zero- or near-zero mean difference in absolute altitude from the corresponding LIDAR point cloud. The DEMs contain substantially more elevation detail (resolution) than the LIDAR data. In the event that LIDAR data is not available for a given frame, the frame is not processed.
The input data were acquired from two locations:
LIDAR Alignment Algorithm
In order to reduce the tilting and scaling issues that sometimes occur in the raw depth maps generated by Photoscan, a rigid transform is used to map these to existing ATM LIDAR data. This is done as a 4-step process:
The trajectory and attitude data used in processing were acquired by the DMS Applanix POS/AV 510 system and provided by the DMS instrument group.
An outline of the processing steps follows:
The underlying accuracy of the measurements can depend on a number of factors, including:
DMS provides natural color or panchromatic tracking imagery from low and medium altitude research aircraft. The system configuration includes a 21 megapixel Canon EOS 5D Mark II digital camera, computer-controlled intervalometer, and an Applanix POS/AV precision orientation system. In-flight operators maximize image quality with adjustments to exposure and intervalometer settings.
Sjöbert, L. E. 2013. Closed-form and Iterative Weighted Least Squares Solutions of Helmert Transformation Parameters, Journal of Geodetic Science. 3(1): 7â€"11, ISSN (Print) 2081-9943, DOI: 10.2478/jogs-2013-0002.
The acronyms used in this document are listed in Table 2.
|ATM||Airborne Topographic Mapper|
|CIRES||Cooperative Institute for Research in Environmental Science|
|DEM||Digital Elevation Model|
|DMS||Digital Mapping System|
|ECEF||Earth-Centered, Earth-Fixed coordinate system|
|FTP||File Transfer Protocol|
|GDAL||Geospatial Data Abstraction Library|
|GeoJPEG||Georeferenced Joint Photographic Experts Group JPEG|
|GeoTIFF||Georeferenced Tagged Image File Format TIFF|
|NASA||National Aeronautics and Space Administration|
|NSIDC||National Snow and Ice Data Center|
|SVD||Singular Value Decomposition|
|URL||Uniform Resource Locator|
03 December 2014
26 January 2015