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Data Set ID:
IGCMG1B

IceBridge CMG 1A Dynamic Gravity Meter Time-Tagged L1B Vertical Accelerations, Version 1

This data set contains vertical acceleration values for Antarctica using the CMG 1A dynamic gravity meter. The data were collected by scientists working on the Investigating the Cryospheric Evolution of the Central Antarctic Plate (ICECAP) project, which is funded by the National Science Foundation (NSF) and the Natural Environment Research Council (NERC) with additional support from NASA Operation IceBridge.

Geographic Coverage

Parameter(s):
  • Geodetics/Gravity > Gravitational Field > Accelerations
Spatial Coverage:

  • N: -53, S: -90, E: 180, W: -180
Spatial Resolution: Not Specified
Temporal Coverage:
  • 14 October 2012
(2014)
Temporal Resolution: Varies
Data Format(s):
  • XML
  • ASCII Text
Platform(s) BT-67
Sensor(s): CMG-GT-1A
Version: V1
Data Contributor(s): Donald Blankenship, Scott Kempf, Duncan Young
Metadata XML: View Metadata Record
Data Citation

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.

Blankenship, D. D., S. D. Kempf, and D. A. Young. 2013, 2014. IceBridge CMG 1A Dynamic Gravity Meter Time-Tagged L1B Vertical Accelerations, 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/KDNRYQC7V2CD. [Date Accessed].

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Detailed Data Description

Format

The data files are in space-delimited ASCII text format. Each data file is paired with an associated XML file. XML files contain file granule and date and time range metadata.

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File and Directory Structure

Data files are organized in folders by date, for example /2013.01.15/, and are available in the https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/IGCMG1B.001/ directory.

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File Naming Convention

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

IGCMG1B_2012339_ICP5_JKB2h_F16T04a_accel.txt

IGCMG1B_2012339_ICP5_JKB2h_F16T04a_accel.txt.xml

IGCMG1B_YYYYDOY_PPP_JKB2h_ANNAa_accel.xxx

Where:

Table 1. Naming Convention
Variable Description
IGCMG1B Short name for IceBridge CMG 1A Dynamic Gravity Meter Time-Tagged Level-1B Vertical Accelerations
YYYY Four-digit year of survey
DOY Day of year of survey
PPP Geographic area (Project)
JKB2h Host platform for timing (System)
TTTT Transect name within Project
accel Acceleration
xxx Indicates ASCII text file .txt, or or XML file .xml
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File Size

File sizes range from approximately 223 KB to 45 MB.

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Volume

The entire data set is approximately 737 MB.

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Spatial Coverage

Spatial coverage for this data set is Antarctica, represented by this extent:

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

Spatial Resolution

Not applicable to these raw instrument outputs.

Projection and Grid Description

WGS-84

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Temporal Coverage

These data were collected from 14 November 2012 to 15 January 2013 as part of ICECAP, NSF, NERC, and Operation IceBridge funded campaigns.

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. Campaigns for this data set typically extend from November to early January.

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Parameter or Variable

Parameter Description

The gravimetry files contain fields as described in Table 2.

Table 2. File Parameter Description
Parameter Units
Year UTC
Day of Year UTC
Second of day UTC
Packet sequence number n/a
Longitude Decimal degrees WGS-84
Latitude Decimal degrees WGS-84
Aircraft elevation at CG antenna Meters WGS-84
Roll, right wing down positive Degrees
Pitch, nose up positive Degrees
Heading, w.r.t north Degrees
Z-axis apparent acceleration recorded on fine +/- 0.5G channel milliGals - 2 second aperiodic filter
Z-axis apparent acceleration recorded on coarse +/- 1.9G channel milliGals - 2 second aperiodic filter
X-axis apparent acceleration milliGals milliGals
Y-axis apparent acceleration milliGals milliGals
Normalized temperature C
Cross coupling term:Y-horizontal acceleration * X-platform tilt milliGals
Cross coupling term:X-horizontal acceleration * Y-platform tilt milliGals
RMS of proof mass vertical displacement nanometers
Vertical accelerometer saturation indicator counts counts

Positions (Fields 5-10) are interpolated from the real time GPS feed and have an accuracy of several meters. They should NOT be used for primary data analysis.

Sample Data Record

Shown below are the first 10 records from the IGCMG1B_2012339_SCT_JKB2h_Y46a_accel.txt date file.

sample data record
Figure 1. Sample Data Record

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Software and Tools

No special tools are required for the ASCII text files.

Quality Assessment

These data are raw instrument outputs and as such their quality is not quantifiable in geophysical units but in physical units of the instrument detectors and internal processing which are not published by the vendor.

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Data Acquisition and Processing

Theory of Measurements

These data are raw outputs from the instrument, consisting of accelerations measured by on-board accelerometers and angles measured by on-board gyroscopes and angle encoders.

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Data Acquisition Methods

These data were obtained through execution of the recommended vendor procedures for its operation. The instrument records data internally for post-flight download. The instrument requires external 4 channel (4 antennas) GPS data in real time, which was provided.

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Derivation Techniques and Algorithms

Techniques as directed in vendor supplied operating instructions for the instrument.

Trajectory and Attitude Data

Trajectory and attitude data from GPS and internal angle encoders are as recorded in the data packets.

Processing Steps

To create these files the raw instrument data were interpreted from native binary to ASCII format and GPS positions were appended to the time tagged data packets.

Version History

On 27 May 2014 the original Version 01 data were replaced with Version 01.1. Version 01.1 data files contain header information including campaign, location, platform, and instrument metadata. The data file names were changed to include the data set short name and .txt extension. New campaigns were added. Campaigns were added, extending the temporal coverage.

Error Sources

Instrumental errors: the gravity instrumentation must be stabilized in temperature over a period of time related to the length of time it has been off and uncontrolled. For these data the instrument was well stabilized.

Environmental conditions: the precise accelerations and attitudes recorded by the gravimeter are subject to degradation by aircraft maneuvering, turbulence and shocks; and to a lesser extent by smooth changes in altitude and turns. The best results are from smooth, straight, level flight as can be determined by examination of the GPS trajectory data and instrument records of accelerometer saturation events.

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Sensor or Instrument Description

These L1B vertical accelerations data were collected using a GT-1A Airborne Gravimeter developed by Gravimetric Technologies and Canadian Micro Gravity.

The GT-1A system is a three axis stabilized gravimeter, with a ±500 Gal dynamic range primary vertical accelerometer. Accelerations are sampled on board at 300 Hz. These are averaged over 16 sample intervals, for an effective sample rate of 18.75 Hz. The system has demonstrated accuracy on the order of 0.5 milligal in airborne surveys with spatial resolutions of a few km.

The data in this set were collected using developmental software in the unit for operations in polar regions. This modification allowed for heading control of the platform via real time input of 4 channel (4 antennas) GPS data.

Positions (Fields 5-10) are interpolated from the real time GPS feed and have an accuracy of several meters. They should NOT be used for primary data analysis.

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References and Related Publications

Vendor Description of Instrument: http://www.canadianmicrogravity.com/pdfs_new/GT_1A.pdf

Vendor Technology Description: http://www.canadianmicrogravity.com/index.php?option=com_content&view=article&id=114&Itemid=108

Related Data Collections

Related Web Sites

Contacts and Acknowledgments

Donald D. Blankenship, Scott Kempf, Duncan Young
University of Texas at Austin
Institute for Geophysics
Austin, TX, 78759-8500

Acknowledgments: 

NASA ICE Bridge grant # NNX11AD33G
NSF Office of Polar Programs logistical support project # G-098-M
Australian Antarctic Division
Institut Polaire Français Paul Emile Victor – IPEV
Jackson School of Geosciences

Document Information

Document Creation Date

31 October 2013

Document Revision Date

22 May 2014

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