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IceBridge CMG 1A Dynamic Gravity Meter Time-Tagged Level-1B Vertical Accelerations

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.

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

The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.

Blankenship, Donald D., Scott Kempf, Duncan Young. 2013. IceBridge CMG 1A Dynamic Gravity Meter Time-Tagged L1B Vertical Accelerations, [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://nsidc.org/data/igcmg1b.html.

Overview

Platform

DC-3T C-GJKB in ICECAP configuration

Sensor

CMG 1A Dynamic Gravity Meter

Spatial Coverage

Antarctica

Spatial Resolution

n/a

Temporal Coverage

22 November 2012 to 04 December 2012

Temporal Resolution

Seasonal

Parameters

Gravimeter acceleration measurements

Data Format

ASCII text

Metadata Access

View Metadata Record

Get Data

FTP

1. Contacts and Acknowledgments

Investigator(s) Name and Title

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

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

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

2. Detailed Data Description

Format

The data files are in space-delimited ASCII text format.

File and Directory Structure

Data files are organized on the FTP site, ftp://n5eil01u.ecs.nsidc.org/SAN2/ICEBRIDGE/IGCMG1B.001/, as described in Figure 1.

directory structure

Figure 1. Directory Structure

File Naming Convention

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

ASB_JKB2h_R22Wa_accel.txt

AAA_JKB2h_ANNAa_accel.txt

Where:

Table 1. Naming Convention
Variable Description
AAA Geographic area
JKB2h Host platform
ANNAa Geographic track line
accel Acceleration
txt ASCII text file

File Size

File sizes range from approximately 223 KB to 45 MB.

Volume

The entire data set is approximately 698 MB.

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

Temporal Coverage

These data were collected as part of ICECAP, NSF, NERC, and Operation IceBridge funded campaigns from 22 November 2012 to 04 December 2012.

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.

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 five records from the 04 December 2012 Antarctica data file: SCT_JKB2h_Y46a_accel.txt

sample data record

Figure 1. Sample Data Record

3. Data Access and Tools

Get Data

Data are available via FTP.

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.

4. 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.

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.

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.

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.

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.

5. 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

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
CIRES Cooperative Institute for Research in Environmental Science
FTP File Transfer Protocol
ICECAP Investigating the Cryospheric Evolution of the Central Antarctic Plate
L1B Processing Level-1B
NASA National Aeronautics and Space Administration
NERC Natural Environment Research Council
NSF National Science Foundation
NSIDC National Snow and Ice Data Center
URL Uniform Resource Locator
UTC Universal Time Code
WGS-84 World Geodetic System 1984

Document Creation Date

31 October 2013

Document Revision Date

.....

Document URL

http://nsidc.org/data/docs/daac/icebridge/igcmg1b/index.html