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IceBridge UAF Lidar Scanner L1B Geolocated Surface Elevation Triplets, Version 1
This data set contains contains scanning laser altimetry data points of Alaska Glaciers acquired using the airborne University of Alaska Fairbanks (UAF) Glacier Lidar system. The data were collected as part of NASA Operation IceBridge funded campaigns.
|Temporal Resolution:||12 month|
|Data Contributor(s):||Chris Larsen|
|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.Larsen, C. 2010, updated 2015. IceBridge UAF Lidar Scanner L1B Geolocated Surface Elevation Triplets, 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/AATE4JJ91EHC. [Date Accessed].
Detailed Data Description
The UAF Lidar Scanner Level-1B Geolocated Surface Elevation Triplets data files are in LAS 1.2 sequential binary format. The LAS file format is a public file format for the interchange of 3-dimensional point cloud data between data users (ASPRS Standards Committee LASer (LAS) File Format Exchange Activities).
Each data file is paired with an associated XML file. XML files contain file level metadata and location, platform, and campaign information.
Data are available on the FTP site in the
https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/ILAKS1B.001/ directory. This directory is organized by date, for example
/2014.08.23/. Folders contain LAS sequential binary files and XML files.
The data files are named according to the following convention and as described in Table 1:
||Short name for IceBridge UAF Lidar Scanner L1B Geolocated Surface Elevation Triplets|
||Four-digit year of data collection|
||Day of Year of acquisition|
||Indicates file type. For example: LAS 1.2 file (.las) or XML (.xml)|
Data files range from approximately 1.3 MB to 2 GB.
XML files range from approximately 4 KB to 64 KB.
The total data set volume is approximately 154 GB.
Spatial coverage for the IceBridge UAF Lidar Scanner Level-1B Geolocated Surface Elevation Triplets campaigns:
Southernmost Latitude: 55° N
Northernmost Latitude: 72° N
Westernmost Longitude: 156° W
Easternmost Longitude: 130° W
The footprint on the ground of the laser shot points is on the order of 20 cm in diameter. Average spacing along path and perpendicular to the flight path is roughly 1 meter by 1 meter, subject to Height Above Ground (HAG) flown and attitude of the aircraft. Preferred HAG is 500 to 600 m. Optimal conditions result in a swath 500 to 600 m wide with 1 meter by 1 meter density.
Projection and Grid Description
The data are provided with Universal Transverse Mercator (UTM) eastings and northings. Easting and northing values are in UTM zones 6, 7, and 8. Geoid values are not included.
These data were collected as part of NASA Operation IceBridge funded campaigns from 19 August 2009 to the present.
IceBridge campaigns are conducted on an annual repeating basis. Alaska campaigns are conducted during May, June, July, August, and September.
The UAF Lidar Scanner Level-1B Geolocated Surface Elevation Triplets data set contains elevation measurements with UTM easting and northing.
Parameters contained in UAF Lidar Scanner Level-1B data files are described in Table 2. Column numbers 1 to 3 in Table 3 represent columns left-to-right in the data. Columns are not numbered in the data files.
|3||Elevation (Height Above Ellipsoid (HAE))||Meters|
Software and Tools
Data Acquisition and Processing
The UAF altimetry data are comprised of a series of point measurements on the surface of glaciers recorded from an aircraft. Each point is derived from a pulsed laser range measurement combined with aircraft Global Positioning System Inertial Measurement Unit (GPS/IMU) positioning and orientation measurements. The footprint on the ground of the laser shot points is on the order of 20 cm in diameter. Coordinates and elevation for each point are referenced in the International Terrestrial Reference Frame (ITRF00) and are accurate to within +/- 30 cm. Longitude/Latitude values are derived by projecting the ITRF coordinates into WGS 84. Easting and northing values are in UTM zones 6, 7, and 8. All vertical data are in HAE.
The GPS records the position of the aircraft every second as it flies over a glacier. The laser continually measures the distance between the aircraft and the glacier surface, and the gyroscope measures the direction the laser is pointing.
The Riegl scanner has a 60 degree beam sweep, range up to 650 m, and measures 20,000 data points per second. The IMU measures the aircraft attitude (pitch, roll, yaw, and rates about those axes) and several other measurements, all at 100 times per second. The Trimble GPS records raw, dual frequency data which is post-processed after the survey against similar data recorded at a fixed GPS base station to provide precise positioning of the aircraft. At typical aircraft speeds and heights data are collected on a roughly 1 meter by 1 meter grid along a 500 meter wide swath (UAF Glacier Lidar System Web page).
The following processing steps are performed by the data provider.
- All GPS processing of the aircraft position uses L1 frequency 1575.42 MHz and L2 frequency 1227.6 MHz data recorded at 5 Hz, processed with the TRACK GPS differential phase kinematic positioning program, a module of the GAMIT/GLOBK software programs from the Department of Earth Atmospheric and Planetary Sciences, MIT. For further information on TRACK, see http://geoweb.mit.edu/~tah/track_example.
- GPS base station coordinates are found using Online Positioning User Service (OPUS). For further information on OPUS, see http://www.ngs.noaa.gov/OPUS/. The kinematic processing and the laser shot point coordinates are referenced to these base station coordinates.
On 21 September 2012, the 2009 and 2010 data were replaced with V01.1 reprocessed data. The reprocessing involved:
- Identifying and correcting infrequent timing shifts wherein the laser scanner data and IMU/GPS data were misaligned by 1 or 2 integer seconds. This only concerned a small handful of files, but the effect can introduce errors on the order of 10's to 100's of meters in horizontal and vertical coordinates of the point cloud data.
- Applying corrected boresight angles, that is, the small angular offsets between the IMU/GPS reference frame and the laser vector. These corrections were applied to all data. The previous, incorrect boresight angles introduced errors on the order of meters to 10's of meters in the horizontal and vertical coordinates of the point cloud data.
- Cleaning of spurious data points that did not represent real targets or surfaces. These appear in the previous versions of these data as random, individual points far away from the surfaces being imaged.
The UAF lidar scanner is a laser altimetry system used for measuring surface elevation changes of glaciers throughout Alaska and western Canada. The altimetry system consists of a highly accurate GPS receiver, a laser, and a gyroscope.
The main components of the UAF lidar scanner are a Riegl LMS-Q240i scanning laser altimeter, an Oxford Technical Solutions Inertial+2 inertial measurement unit, a Trimble R7 geodetic GPS receiver, and a small form factor PC for data logging.
References and Related Publications
Contacts and Acknowledgments
University of Alaska Fairbanks
903 Koyukuk Drive
Fairbanks, Alaska 99775, USA
This program has been supported by grants from NASA, NOAA and NSF. Current support comes from NSF Arctic Natural Sciences grant ARC-0612537 and from NASA's Operation Ice Bridge, Earth Science Project Office, Grant NNX09AP54G.
Document Creation Date
19 December 2011
Document Revision Date
08 February 2012
16 July 2012
16 December 2014
10 June 2015