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IceBridge DMS L1B Geolocated and Orthorectified Images, Version 1
This data set contains Level-1B imagery taken from the Digital Mapping System (DMS) over Greenland and Antarctica. The data were collected as part of Operation IceBridge funded aircraft survey campaigns.
|Platform(s)||DC-8, HU-25C, P-3B|
|Data Contributor(s):||Roseanne Dominguez|
|Metadata XML:||View Metadata Record|
As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.Dominguez, R. 2010, updated 2016. IceBridge DMS L1B Geolocated and Orthorectified Images, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/OZ6VNOPMPRJ0. [Date Accessed].
Detailed Data Description
The DMS airborne digital camera acquires high resolution natural color and panchromatic imagery from low and medium altitude research aircraft. Measurements are embedded in the image files, including coordinate and projection information, GPS Date, GPS Time, Pitch, Roll, Altitude, FStop, Shutter Speed, and Mode.
The DMS Level-1B Geolocated and Orthorectified Images are GeoTIFF files. For each GeoTIFF there is an associated browse file in JPEG format. and an XML containing instrument, sensor, and campaign metadata.
Data are available on the n5eil01u.ecs.nsidc.org FTP site in the
ftp://n5eil01u.ecs.nsidc.org/DP4/ICEBRIDGE/IODMS1B.001/ directory. Within this directory are data subdirectories named for each year, month, and day of data collection, for example /2009.10.16/.
The DMS files are named according to the following convention and as described in Table 2:
||Digital Mapping System camera|
||Frame Number (all GeoTIFF files have 5 digit frame numbers)|
||Four-digit year image acquired|
||Two-digit month image acquired|
||Two-digit day image acquired|
||Two-digit hour image acquired|
||Two-digit minute image acquired|
||Two-digit second image acquired|
||Two-digit hundredths of a second image acquired|
||indicates output file: e.g. .tif|
NOTE: File names for the 2009 Antarctica campaign include a V02 indication, for example:
See the Version History and Special Processing Notes sections for more information about the 2009 Antarctica data.
XML metadata file names are the same as the GeoTIFF files, but use extension .tif.xml. Example:
Browse file names are the same as GeoTIFF files, but use extension .tif_brws.jpg. Example:
NOTE on Recent Insert files: During ingest of new IODMS1B data, "recent insert" files are temporarily stored with the data files. The recent insert files contain listings of the data files that have been added to the data set. After ingest is complete, the recent insert files are removed. Example file name:
GeoTIFF files range from approximately 2 MB to 248 MB.
The entire data set is approximately 68 TB.
Spatial coverage for the DMS Level-1B campaigns include Greenland, Antarctica, and Arctic and Antarctic Sea Ice areas. In effect, this represents the two coverages noted below.
Arctic and Greenland:
Southernmost Latitude: 60° N
Northernmost Latitude: 90° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Southernmost Latitude: 90° S
Northernmost Latitude: 53° S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
The DMS Level-1B spatial resolution ranges from 0.015 m to 2.5 m. Pixel size is dependent on flight altitude and referenced DEM. Spatial resolution is 10 cm for images acquired at 1500 ft AGL.
Projection and Grid Description
Arctic: Polar Stereographic Standard Parallel 70° N, Longitude of the origin (central meridian): 45° W, WGS 84 ellipsoid.
Antarctica: Polar Stereographic Standard Parallel 71° S, Longitude of the origin (central meridian): 0°, WGS 84 ellipsoid.
Note: For the 2010 Antarctica campaign only, the standard parallel for sea ice images is 70° S.
These data were collected as part of NASA Operation IceBridge funded campaigns from 16 October 2009 to 18 Noember 2016.
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 DMS Level-1B Geolocated and Orthorectified Images are natural color and panchromatic imagery. The GeoTIFF files include the following embedded information: GPS Date, GPS Time, Pitch, Roll, Altitude, FStop, Shutter SPeed, Mode, and Coordinate and Projection information.
Sample Data Record
The image below is a selected area of the image file:
The listing below shows the information embedded in the GeoTIFF image file
DMS_1000109_01938_20091016_17423840.tif displayed above. 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.
Software and Tools
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.
Data Acquisition and Processing
This DMS data processing package is based on a rigorous camera model for perspective scene generation and mapping from image plane to the ground. In order to transform from 2D image frame to 3D world coordinates, camera focal length, pixel size, principal point, lens distortion coefficients, and camera position and attitude (Roll, Pitch, and Heading) must be known. These parameters are used in a photogrammetric rotation between image-plane and target coordinates process to orthorectify images into a real world coordinate on a pixel-by-pixel basis.
Two instruments are used in the airborne data acquisition: an Applanix POS/AV navigation system and Canon EOS II digital camera. The POS/AV is a combined inertial measurement unit (IMU) and Global Positioning System (GPS) and provides precise position and attitude information.
The basic photogrammetry relation between a point (x, y) on the image frame to the ground surface point (Xg,Yg,Zg) can be expressed as Equation 1:
||Camera rotation matrix to transform between 2D image frame and 3D grid north coordinates.|
||Image frame point vector of (x-xp, y-yp, -ƒ), where (xp, yp) is principal point, and ƒ is focal length.|
||Ground surface point vector of (Xg-X0, Yg-X0, Zg-Z0), where (X0, Y0, Z0) is the perspective center vector.|
Rcam rotation matrix in Equation 1 uses a grid north coordinate system with three rotation angles as Omega, Phi, Kappa. However, the navigation system collects Roll, Pitch, and Heading angles with a true north coordinate and differ from Omega, Phi, and Kappa angles.
Assuming the navigation system and camera offset can be measured and adjusted, a rotation correction (Rb) between IMU and camera angular misalignment can be estimated with a boresight angle correction procedure. Rcam rotation matrix can add the correction matrix (Rb) as in Equation 2:
||Rotation correction between IMU and camera angular misalignment.|
||Rotation matrix with Omega, Phi, and Kappa without rotation correction between navigation system and DMS camera.|
The orientation of the DMS camera is 90 degrees counter clockwise from the flight/navigation direction. Rnav in Equation 2 is therefore rewritten as in Equation 3:
||Rotation matrix for the 90 degree counter clockwise difference between flight direction and camera mounting direction.|
||Rotation matrix to correct between grid north and true north.|
||Matrix transpose of Rgnav, a rotation matrix with Roll, Pitch, Yaw (where Yaw = -Heading).|
DMS acquires standard JPEG imagery, which are stored via Ethernet on a supporting laptop computer. This computer also runs the EOS camera utility software to monitor and control image exposure. Frame capture is controlled using an external intervalometer. The intervalometer provides a Transistor-Transistor-Logic (TTL) pulse to the navigation system which enables precise timing for each image capture.
1. DMS Camera Calibration
Lens calibration is fundamental to rigorous camera modeling. It is used to eliminate geometric distortion. Calibrated camera interior correction parameters include:
- Focal length
- Principal point (xp, yp)
- 3rd-order (k1), 5th-order (k2), and 7th-order (k3) terms of radial distortion correction
- Coefficients of decentering distortion (p1, p2)
The corrected image frame coordinates (xc, yc) can be calculated from the measured coordinates (xm, ym) by using the Equations 4 and 5:
||Measured coordinate x|
||Principle point x|
||Measured coordinate y|
||Principle point y|
x and y are now with respect to the principal point:
||Distance from the principal point of the lens|
||Radial distortion from the principal point|
||3rd-order term of radial distortion correction|
||5th-order term of radial distortion correction|
||7th-order term of radial distortion correction|
||Corrected image frame coordinate x|
||Corrected image frame coordinate y|
||Coefficients of decentering distortion|
2. Offset Adjustment between Navigation System and Camera
The three dimensional distances between camera principle point, IMU, and GPS antenna are integrated into the final navigation data solution. This enables the rotation matrix Rb to properly represent the boresight correction angles.
The measured vector (dx, dy, dz) are fully integrated in the post flight navigation data process. Therefore, the camera position is adjusted to the same origin of navigation system.
3. Boresight Correction
If we combine Equations 2 and 3, Rcam can be rewritten as:
Therefore, the angular misalignment (Rb) between navigation system and camera can be estimated if Pg and Pf are known from equation (1).
Pg vector can be derived from GPS measured ground control points or a high resolution orthorectified reference map with DEM. Pg related Pf vector can be located in the raw image frame. Rotation matrix Rc is a constant matrix for each DMS configuration. Rotation matrix Rg is a constant matrix for a targeted area with the converged angle difference between grid north and true north. However, rotation matrix Rb can vary with physical and environmental conditions as well as navigation system errors. Rb is assumed to be relatively stable and errors from physical and environmental factors are minimized if the system installation is fixed under the same condition.
In the boresight correction process, we select three to four continuous frames in multiple flight directions to cover a targeted area. Numerous ground control points, either from a high resolution reference map or GPS surveyed points, are picked for each frame. Boresight angles are derived based on Equations 1 and 10 from Rb for each selected frame. Finally, boresight angles are averaged from all frames.
4. DMS Production Software Package
The DMS software package developed for data production is an integration of public domain software with an in-house user interface to facilitate the entire production process. The public domain software includes:
- Open Source Software Image Map (OSSIM) (http://www.ossim.org). OSSIM is a publically available high performance engine for photogrammetry, remote sensing, image processing, and geographical information systems.
- Geospatial Data Abstraction Library (GDAL). GDAL is a translator library for raster geospatial data formats and processing. It is available under an X/MIT style Open Source license by the Open Source Geospatial Foundation (http://www.gdal.org).
OSSIM is written in C++ with object-orientated modules and classes. A customized sensor model is integrated in the OSSIM modules and recompiled for use in DMS production. The front end interface is developed in Perl to make the OSSIM and GDAL libraries and utilities more accessible.
Special processing notes regarding each deployment to date are provided below.
Special Processing Notes
2012 Antarctica Campaign
GeoTIFF files were produced using the RADARSAT 200 m DEM. GEOID reference is established by DEM. Sea Ice imagery referencing EGM2008 are identified with a COMMENT tag in the GeoTIFF. There are areas were DEM and aircraft converge and where DEM exceeds aircraft height. These frames were projected with zero elevation as input and altitude above terrain fixed to 250 m. Affected frames are identified with COMMENT tags in the GeoTIFF, where each data issue is explicitly noted. All output reference NSIDC Antarctic stereographic projections. There is one exception: imagery acquired over California reference standard geographic lat/long and were produced using the National Elevation Dataset 10 m DEM.
2012 Greenland Campaign
Geotiff files were produced using the GLAS/ICESat 1 km Laser Altimetry DEM. GEOID reference is established by DEM. Sea ice imagery referencing EGM2008 are identified with a COMMENT tag in the geotiff. There are areas were DEM and aircraft converge and where DEM exceeds aircraft height. These frames were projected with zero elevation as input and alitude above terrain fixed to 230 m. Affected frames are identified with COMMENT tags in the geotiff, where each data issue is explicitly noted. All output references NSIDC Antarctic stereographic projections. There is one exception: imagery acquired over Virginia's East Coast reference standard geographic lat/long and were produced using the National Elevation Dataset 10 m DEM.
2011 Antarctica Campaign
GeoTIFF files were produced using the RADARSAT 200 m DEM. GEOID reference is established by DEM. Sea Ice imagery referencing EGM2008 are identified with a COMMENT tag in the GeoTIFF. There are areas were DEM and aircraft converge and where DEM exceeds aircraft height. These frames were projected with zero elevation as input and altitude above terrain fixed to 230 m. Affected frames are identified with COMMENT tags in the GeoTIFF, where each data issue is explicitly noted. All output references NSIDC Antarctic stereographic projections. There is one exception: imagery acquired over Southern California reference standard geographic lat/long and were produced using the National Elevation Dataset 10m DEM.
2011 Greenland Campaign
GeoTIFF files were produced using the GLAS/ICESat 1 km Laser Altimetry Digital Elevation Model of Greenland. There are areas were DEM and aircraft converge. Affected frames are identified with a COMMENT tag in the GeoTIFF. Frames where DEM exceeds aircraft height were projected with zero elevation as input. Frames where Aircraft-DEM delta was less than 65 m were projected using a 2D model.
2010 Antarctica Campaign
For the 2010 Antarctica campaign only, the standard parallel for sea ice images is 70° S. The standard parallel for land ice images for this campaign is 71° S.
2009 Antarctica Campaign
A refined camera model was implemented, as well as enhanced boresight angles. In addition RADARSAT 200 m DEM was used as ground reference input. A new metadata field has been embedded in each GeoTIFF referencing version differences. There are areas were DEM and aircraft converge. Affected frames are identified with an additional COMMENT tag in the GeoTIFF. Frames where the DEM exceeds aircraft height were projected with zero elevation as input. Frames where Aircraft-DEM delta was less than 65 m were projected using a 2D model. Most imagery were acquired in panchromatic mode, but all provided output is 3-banded imagery. Flights where some imagery were collected in both modes were processed as "color" as identified in the GeoTIFF embedded metadata.
DMS is a commercial off the shelf camera. The time stamp in the Level-0 jpeg imagery is from the internal camera clock. The camera's intervalometer is tied to the Applanix. For the Level-1B data, a series of linear regressions is used to map out the time lag and sync the camera shutters to the nav data. That synched time is embedded into the GeoTIFF along with other metadata.
The following processing steps are performed by the data provider.
DMS geo-rectified TIFF imagery is supplied on a best effort basis. Processing steps include (1) time sync between the DMS internal clock and POS/AV, (2) definition of frame geometry to include bore-sight adjustment, lens distortion and digital elevation model (DEM) inputs, and (3) GeoTIFF production with ancillary documentation and a variety of map projection allowances.
The camera's internal clock drifts over time. Alone it cannot be used to sync to corresponding navigation data. Thus an intervalometer is used to trigger each shutter function. This is captured via a TTL pulse as an Applanix event.
The cameras are calibrated prior to each deployment using the Photometrix Australis package. The calibration provides focal length, principal point, terms of radial distortion, as well as coefficients of de-centering distortion.
Boresight angles are calculated using High Resolution Ortho-rectified images (HRO) or other precise surveys and best available elevation data. Three or four continuous frames from multiple flight headings are used to derive the alignment differences between the camera's focal plane and the POS/AV. Ten to twelve broadly spaced control points are selected for each frame.
Once the boresight and lens distortion corrections are applied, a 3D ray trace is performed to generate the final GeoTIFF. The quality and resolution of DEM is a key factor in geo-location accuracy. The distance between the focal plane and ground determines the footprint of each frame. Over varying terrain the frame-edge location will be severely degraded if DEM resolution significantly differs from pixel geometry.
There were some targets where the available DEM exceeded aircraft height or where the DEM converged towards aircraft altitude. Spring 2013 also had a single flight with a polar crossing. Any frame requiring additional processing has extra embedded metadata.
Version 01.1 re-processed 2009 Antarctica DMS data became available April 12, 2011, and replaced the previous version. The 2009 Antarctica DMS data required re-processing because the data were projected using the SRTMplus Digital Elevation Model (DEM). This DEM references the sea floor for all non-terrestrial locations. In addition, during re-processing, a more refined boresight model was employed and provides a more accurate attitude reference. See the Special Processing Notes section for more on the 2009 Antarctica campaign.
Version 01.2 data for 2012 Greenland. On March 18, 2013, 9505 frames were replaced with reprocessed data for the 11 April 2012 East Glaciers-1 flight. If you downloaded the 11 April 2012 files prior to 18 March 2013, it is recommended that you re-download them. The original frames from the flight's Level-1B files were smaller and of lower resolution than images earlier in the flight at the same aircraft height above ground level (AGL) of 470-480 m. The affected 11 April 2012 frames include: 09186 to 09189, 09243 to 09268, 09270 to 09368, 09376 to 09385, 09391 to 10428, 10488 to 10733, and 10833 to 18914. See the File Naming Convention section for reference to frame numbers.
2015 Antarctica: during the 2015 Antarctica campaign the aircraft window had to be repaired in the field. The replacement window was green and tinted the imagery. Affected frames include an additional COMMENT in the GeoTIFF file describing the issue.
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.
References and Related Publications
Contacts and Acknowledgments
Airborne Sensor Facility
NASA Ames Research Center
Moffett Field, CA 94035-1000 USA
DMS is supported by the NASA Airborne Science Program. Data collection and exceptional image quality is the result of the phenomenal efforts of our field team: Robert Billings, Kent Dunwoody, Eric Fraim, Dennis Gearhart and James Jacobson. Software integration and development was provided by Dr. Haiping Su (UCSC).
Document Creation Date
15 November 2012
Document Revision Date
11 January 2013
19 February 2013
01 October 2013
28 May 2014
10 November 2014
11 May 2015
21 August 2015
26 May 2016
13 June 2016
25 August 2016
23 November 2016
08 February 2017