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IceBridge DMS L1B Geolocated and Orthorectified Images

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.

Operation IceBridge products may include test flight data that are not useful for research and scientific analysis. Test flights usually occur at the beginning of campaigns. Users should read flight reports for the flights that collected any of the data they intend to use. Check IceBridge campaign Flight Reports for dates and information about test flights.

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

Citing These Data

We kindly request that you cite the use of this data set in a publication using the following citation example. For more information, see our Use and Copyright Web page.

Dominguez, Roseanne. 2010, updated 2014. IceBridge DMS L1B Geolocated and Orthorectified Images, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://nsidc.org/data/iodms1b.html.

Overview

Platform

NASA DC-8, NASA P-3B

Sensor

DMS

Spatial Coverage

Antarctica, Greenland, and Arctic and Antarctic Sea Ice

Spatial Resolution

Nominal 10 cm at 1500 feet AGL

Temporal Coverage

16 October 2009 to the present.

Temporal Resolution

Seasonal

Parameters

Natural Color and Panchromatic Imagery

Data Format

GeoTIFF, JPEG, XML

Metadata Access

View Metadata Record

Get Data

FTP

1. Contacts and Acknowledgments

Investigator(s) Name and Title

Roseanne Dominguez
Airborne Sensor Facility
NASA Ames Research Center
MS 244-15
Moffett Field, CA 94035-1000 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

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).

2. 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.

Format

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 metadata file.

File and Directory Structure

Data are available on the n4ftl01u.ecs.nasa.gov FTP site in the ftp://n5eil01u.ecs.nsidc.org/SAN/ICEBRIDGE/IODMS1B.001/ directory. Within this directory, there are data subdirectories named for each year, month, and day of data collection, for example /2009.10.16/.

File Naming Convention

The DMS files are named according to the following convention and as described in Table 1:

DMS_1000109_00551_20091016_15114115.tif

DMS_fffffff_FFFFF_YYYYMMDD_HHmmsshh.tif

Where:

Table 1. DMS GeoTIFF File Naming Convention
Variable Description
DMS Digital Mapping System camera
fffffff Flight number
FFFFF Frame Number (all GeoTIFF files have 5 digit frame numbers)
YYYY Four-digit year image acquired
MM Two-digit month image acquired
DD Two-digit day image acquired
HH Two-digit hour image acquired
mm Two-digit minute image acquired
ss Two-digit second image acquired
hh Two-digit hundredths of a second image acquired
.tif indicates GeoTIFF file

XML metadata file names are the same as the GeoTIFF files, but use extension .tif.xml. Example: DMS_1000109_00551_20091016_15114115_V02.tif.xml

Browse file names are the same as GeoTIFF files, but use extension .tif_brws.jpg. Example: DMS_1000109_00551_20091016_15114115_V02.tif_brws.jpg

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: DPRecentInserts_IODMS1B_001_20130820.

File Size

GeoTIFF files range from approximately 2 MB to 248 MB.

Volume

The entire data set is approximately 38 TB.

Spatial Coverage

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

Antarctic:
Southernmost Latitude: 90° S
Northernmost Latitude: 53° S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E

Spatial Resolution

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.

Antarctic: Polar Stereographic Standard Parallel 71° S, Longitude of the origin (central meridian): 0°, WGS 84 ellipsoid.

Temporal Coverage

These data were collected as part of NASA Operation IceBridge funded campaigns from 16 October 2009 to the present.

Temporal Resolution

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.

Parameter or Variable

Parameter Description

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: DMS_1000109_01938_20091016_17423840.tif

sample data record

Figure 1. Sample Data Record

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.

sample data record embedded information

3. Data Access and Tools

Get Data

Data are available via FTP.

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.

4. Data Acquisition and Processing

Theory of Measurements

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:

Equation 1 (Equation 1)

Where:

Table 2. Relation Between a Point on the Image Frame to the Ground Surface Point
Variable Description
k Scale factor.
Rcam 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.
Pg 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:

Equation 2 (Equation 2)

Where:

Table 3. Camera Rotation Matrix
Variable Description
Rb Rotation correction between IMU and camera angular misalignment.
Rnav 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:

Equation 3 (Equation 3)

Where:

Table 4. Rotation Matrix
Variable Description
Rc Rotation matrix for the 90 degree counter clockwise difference between flight direction and camera mounting direction.
Rg Rotation matrix to correct between grid north and true north.
Trans(Rgnav) Matrix transpose of Rgnav, a rotation matrix with Roll, Pitch, Yaw (where Yaw = -Heading).

Data Acquisition Methods

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.

Derivation Techniques and Algorithms

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:

  1. Focal length
  2. Principal point (xp, yp)
  3. 3rd-order (k1), 5th-order (k2), and 7th-order (k3) terms of radial distortion correction
  4. 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:

Equation 4 (Equation 4)

Equation 5 (Equation 5)

Where:

Table 5. Corrected Image Frame Coordinates
Variable Description
xm Measured coordinate x
xp Principle point x
ym Measured coordinate y
yp Principle point y

x and y are now with respect to the principal point:

Equation 6 (Equation 6)

Equation 7 (Equation 7)

Equation 8 (Equation 8)

Equation 9 (Equation 9)

Where:

Table 6. x and y to Principle Point
Variable Description
r Distance from the principal point of the lens
dr Radial distortion from the principal point
k1 3rd-order term of radial distortion correction
k2 5th-order term of radial distortion correction
k3 7th-order term of radial distortion correction
xc Corrected image frame coordinate x
yc Corrected image frame coordinate y
p1 and p2 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:

Equation 10 (Equation 10)

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:

  1. 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.
  2. 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.

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.

Processing Steps

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 History

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.

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 above for reference to frame numbers.

Sensor or Instrument Description

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.

5. References and Related Publications

Farr, T. G., et al. 2007. The Shuttle Radar Topography Mission, Rev. Geophys., 45:RG2004, doi:10.1029/2005RG000183.

Related Data Collections

Related Web Sites

  • NASA Digital Mapping System Web page (http://asapdata.arc.nasa.gov/dms/).
  • IceBridge Data Web site at NSIDC (http://nsidc.org/data/icebridge/index.html).
  • IceBridge Web site at NASA (http://www.nasa.gov/mission_pages/icebridge/index.html).
  • ICESat/GLAS Web site at NASA Wallops Flight Facility (http://glas.wff.nasa.gov/).
  • ICESat/GLAS Web site at NSIDC (http://nsidc.org/daac/projects/lidar/glas.html).

6. Document Information

Acronyms and Abbreviations

The acronyms used in this document are listed in Table 6.

Table 6. Acronyms and Abbreviations
Acronym Description
AGL Above Ground Level
CIRES Cooperative Institute for Research in Environmental Science
DEM Digital Elevation Model
DMS Digital Mapping System
FTP File Transfer Protocol
GDAL Geospatial Data Abstraction Library
GeoTIFF Georeferenced Tagged Image File Format TIFF
GPS Global Positioning System
JPEG Joint Photographic Experts Group file format
L1B Processing Level-1B
IMU Interial Measurement Unit
NASA National Aeronautics and Space Administration
NSIDC National Snow and Ice Data Center
OSSIM Open Source Software Image Map
POS/AV Position and Orientation System / Airborne Vehicle
SRTM Shuttle Radar Topography Mission
TTL Transistor-Transistor-Logic
URL Uniform Resource Locator
XML Extensible Markup Language

Document Creation Date

15 November 2012

Document Revision Date

11 January 2013

19 February 2013

01 October 2013

28 May 2014

Document URL

http://nsidc.org/data/docs/daac/icebridge/iodms1b/index.html