IceBridge UAF GPS/IMU L1B Corrected Position and Attitude Data

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.

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

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, Chris. 2011. IceBridge UAF GPS/IMU L1B Corrected Position and Attitude Data, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center.



DeHavilland Otter DHC-3


Oxford Technical Solutions Inertial+2 Inertial Measurement Unit
Trimble R7 Geodetic GPS Receiver

Spatial Coverage


Spatial Resolution


Temporal Coverage

19 August 2009 to present

Temporal Resolution




Data Format


Metadata Access

View Metadata Record

Get Data



1. Contacts and Acknowledgments

Investigator(s) Name and Title

Chris Larsen
Geophysical Institute
University of Alaska Fairbanks
903 Koyukuk Drive
Fairbanks, Alaska 99775 USA

Technical Contact

NSIDC User Services
National Snow and Ice Data Center
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services


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.

2. Detailed Data Description


The data files are in ASCII format.

File and Directory Structure

Data files are organized on the FTP site,, as described in Figure 1.

directory structure

Figure 1. Directory Structure

File Naming Convention

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

File Size

Data files range from approximately 45 MB to 251 MB.


The total data set volume is approximately 3.6 GB.

Spatial Coverage

Spatial coverage for the UAF GPS/IMU L1B Corrected Position and Attitude data:

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

Temporal Coverage

These data were collected as part of NASA Operation IceBridge funded campaigns from 19 August 2009 to the present.

Temporal Resolution

IceBridge campaigns are conducted on an annual repeating basis. Alaska campaigns are conducted during May, June, July, August, and September.

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

Below is 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

3. Data Access and Tools

Get Data

Data are available via:



Software and Tools

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

4. Data Acquisition and Processing

These data are position and attitude of the inertial platform. They are recorded at 100 Hz by an Oxford Technical Solutions (OxTS) Inertial+2 IMU coupled with a Trimble R7 GPS.

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 datasets are merged in post processing to provide the .pos files with 100 Hz resolution.

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 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
  2. GPS base station coordinates are found using Online Positioning User Service (OPUS). For further information on OPUS, see 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 OxTS program "RTpostprocess". The results are output from this program in the .pos format provided.

Error Sources

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

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.

5. References and Related Publications

Johnson, A. J. 2012. Estimating the Mass Balance of Glaciers in the Glacier Bay Area of Alaska and British Columbia. M.S. Thesis, Geology and Geophys. Dept., Univ. Alaska, Fairbanks, AK.

Related Data Collections

Related Web Sites

GAMIT-GLOBK, MIT Department of Earth Atmospheric and Planetary Sciences (

IceBridge Data Web site at NSIDC (

IceBridge Web site at NASA (

ICESat/GLAS Web site at NASA Wallops Flight Facility (

ICESat/GLAS Web site at NSIDC (

NOAA OPUS: Online Positioning User Service (

UAF Glacier Lidar System Web page (

6. Document Information

Acronyms and Abbreviations

The acronyms used in this document are listed in Table 3.

Table 3. Acronyms and Abbreviations
Acronym Description
ASCII American Standard Code for Information Interchange
ASPRS American Society for Photogrammetry and Remote Sensing
CIRES Cooperative Institute for Research in Environmental Science
FTP File Transfer Protocol
GPS Global Positioning System
IMU Inertial Measurement Unit
ITRF International Terrestrial Reference Frame
L1B Processing Level-1B
L1 L1 is a civilian-use GPS signal broadcast on the 1575.42 MHz frequency, that currently contains the course acquisition signal used by all current GPS users. Also known as L1C.
L2 L2 is a civilian-use GPS signal broadcast on the 1227.6 MHz frequency. Also known as L2C.
NASA National Aeronautics and Space Administration
NOAA National Oceanic and Atmospheric Administration
NSF National Science Foundation
NSIDC National Snow and Ice Data Center
OPUS Online Positioning User Service
OxTS Oxford Technical Solutions
UAF University of Alaska Fairbanks
URL Uniform Resource Locator
UTM Universal Transverse Mercator
WGS-84 World Geodetic System 1984

Document Creation Date

08 March 2013

Document Revision Date

Document URL