Data Set ID:

IceBridge UAF GPS/IMU L1B Corrected Position and Attitude Data, Version 1

This data set contains Global Positioning System (GPS) and Inertial Measurement Unit (IMU) positioning and orientation measurements for the University of Alaska Fairbanks Glacier lidar system campaigns. The data were collected as part of Operation IceBridge funded aircraft survey campaigns.

This is the most recent version of these data.

Version Summary:

Initial release

BASIC Level of Service

Data: Data integrity verified

Documentation: Key metadata and links to supporting documentation available

User Support: Assistance with data access and basic data usage

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Data Format(s):
  • ASCII Text
Spatial Coverage:
N: 72, 
S: 55, 
E: -130, 
W: -156
Platform(s):AIRCRAFT, DHC-3
Spatial Resolution:
  • Varies x Varies
Temporal Coverage:
  • 19 August 2009 to 12 September 2011
Temporal ResolutionVariesMetadata XML:View Metadata Record
Data Contributor(s):Chris Larsen

Geographic Coverage

Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login.

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. 2011. IceBridge UAF GPS/IMU L1B Corrected Position and Attitude Data, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: [Date Accessed].

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Detailed Data Description


The data files are in ASCII format.

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File and Directory Structure

Data files are organized on the following HTTPS site:
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File Naming Convention

Example file name:


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


Table 1. File Naming Convention
Variable Description
IPUAF1B Short name for IceBridge UAF GPS/IMU L1B Corrected Position and Attitude Data
ascii Indicates ASCII data file
DHC-3 DeHavilland Otter aircraft
YYYY Four-digit year of data collection
MM Two-digit month of data collection
DD Two-digit day of data collection
xxxxxx_x Hour, minute and second of start time of collection
.pos Indicates positional data
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File Size

Data files range from approximately 45 MB to 251 MB.

The total data set volume is approximately 3.6 GB.

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Spatial Coverage

Spatial coverage includes Alaska, as noted by the spatial extents below:

Southernmost Latitude: 55° N
Northernmost Latitude: 72° N
Westernmost Longitude: 156° W
Easternmost Longitude: 130° W

Spatial Resolution

Varies, measured in decimal degrees longitude and latitude, eight decimal places.

Projection and Grid Description

Geographic, WGS-84

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Temporal Coverage

19 August 2009 to 12 September 2011

Temporal Resolution

IceBridge campaigns are conducted on an annually repeating basis; Alaska campaigns are typically conducted from May through September.

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Parameter or Variable

Parameter Description

Parameters contained in UAF GPS/IMU L1B Corrected Position and Attitude data files are described in Table 2. Columns 1 to 7 in Table 2 represent columns left-to-right in the data. Columns are not numbered in the data files.

Table 2. Parameter Description and Units
Column Description Units
1 Time UTC
2 Latitude Degrees
3 Longitude Degrees
4 Height Meters
5 Roll Degrees
6 Pitch Degrees
7 Heading Degrees

Sample Data Record

Figure 1 shows an excerpt of the data file IPUAF1B_ascii_DHC-3_20110530_022658_1.pos. The seven fields in each record correspond to the columns described in Table 2.

sample data record
Figure 1. Sample records from the data file IPUAF1B_ascii_DHC-3_20110530_022658_1.pos.
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Software and Tools

The data files may be opened by any ASCII text reader.

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Data Acquisition and Processing

The data represent position and attitude of the inertial platform. They were recorded at 100 Hz by an Oxford Technical Solutions (OxTS) Inertial+2 IMU coupled to a Trimble R7 geodetic GPS receiver.

Data Acquisition Methods

The IMU data are recorded on the IMU at 100 Hz. The GPS data are recorded on the GPS at 5 Hz. The two data sets are merged during the post-processing phase to provide the .pos files with 100 Hz resolution.

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Derivation Techniques and Algorithms

Processing Steps

The following processing steps are performed by the data provider:

  1. All GPS processing of the aircraft position uses L-1 frequency (1575.42 MHz) and L-2 frequency (1227.6 MHz) data recorded at 5 Hz. The data are 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 at MIT.
  2. GPS base station coordinates are found using the Online Positioning User Service (OPUS). The kinematic processing and the laser shot point coordinates are referenced to these base station coordinates.
  3. The IMU raw data are post-processed and blended with the GPS post-processed solution using the OxTS program "RTpostprocess". This program outputs files in the .pos format.

Error Sources

Typical errors sources include the normal GPS post-processing kinematic solution concerns, including the loss of lock from aircraft maneuvers and ionosphere noise.

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Sensor or Instrument Description

The main components of the GPS/IMU are an Oxford Technical Solutions Inertial+2 inertial measurement unit and a Trimble R7 geodetic GPS receiver.

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References and Related Publications

Contacts and Acknowledgments

Chris Larsen
Geophysical Institute
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 the NSF Arctic Natural Sciences grant ARC-0612537 and from NASA's Operation Ice Bridge, Earth Science Project Office, Grant NNX09AP54G.

Document Information


March 2013


March 2019

No technical references available for this data set.

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