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IceBridge BGM-3 Gravimeter L1B Time-Tagged Accelerations, Version 1
This data set contains vertical acceleration values for Antarctica using the BGM-3 Gravimeter. The data were collected by scientists working on the the International Collaborative Exploration of the Cryosphere through Airborne Profiling (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.
|Spatial Resolution:||Not Specified|
|Data Contributor(s):||Donald Blankenship, Scott Kempf, Duncan Young, Thomas Richter, Martin Siegert, Jason Roberts, Tas van Ommen, Emmanuel Lemeur|
|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.Blankenship, D. D., S. D. Kempf, D. A. Young, T. G. Richter, M. J. Siegert, J. L. Roberts, T. van Ommen, and E. Lemeur. 2012, updated 2014. IceBridge BGM-3 Gravimeter L1B Time-Tagged 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/10.5067/5CHZMTE5DLU8. [Date Accessed].
Detailed Data Description
The data files are in space-delimited ASCII text format, with a header offset by # leading characters, corresponding to the NASA Aerogeophysical ASCII data standard. Each data file is paired with an associated XML file. The XML files contain location, platform, and instrument metadata.
Data are available on the FTP site in the
https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/IGBGM1B.001/ directory. Within this directory are folders organized by date, for example
Data stored in the
/2008.12.31/ folder were collected as part of the 2009 campaign.
The ASCII text files are named according to the following convention and as described in Table 1:
||File name prefix indicating IceBridge BGM-3 Gravimeter L1B Time-Tagged Accelerations|
||Four-digit year of survey|
||Day of year of survey|
||Geographic track line|
||Indicates ASCII text file (.txt), or XML file (.xml)|
The data files range from approximately 16 KB to 1.5 MB.
XML files range from approximately 10 KB to 56 KB.
The entire data set is approximately 204 MB.
These data were primarily collected over the Wilkes Subglacial Basin and Aurora Subglacial Basin in East Antarctica.
Spatial coverage for this data set is Antarctica, represented by this extent:
Southernmost Latitude: 90° S
Northernmost Latitude: 53° S
Westernmost Longitude: 90° E
Easternmost Longitude: 180° E
Not applicable to these raw instrument outputs.
Projection and Grid Description
WGS-84 ellipsoid; ITRF 2008
These data were collected from 31 December 2008 to 24 December 2011 as part of ICECAP, NSF, NERC, and Operation IceBridge funded campaigns. Data collected in late December 2008 are part of the 2009 campaign.
ICECAP campaigns were conducted on an annual basis. East Antarctic campaigns for this data set typically extend from November to early January.
The gravimeter L-1B time-tagged accelerations files contain fields as described in Table 2.
|YEAR||Year of survey||UTC|
|DOY||Day of Year of survey||UTC|
|SOD||Second of day||UTC|
|SEQ||Packet sequence number||n/a|
|LON||Longitude||Decimal degrees WGS-84|
|LAT||Latitude||Decimal degrees WGS-84|
|AC-ELEVATION||Aircraft elevation at CG antenna||Meters WGS-84|
|ROLL||Roll, right wing down positive||Degrees|
|PITCH||Pitch, nose up positive||Degrees|
|HEADING||Heading, w.r.t north||Degrees|
Sample Data Record
A sample of the data file:
IGBGM1B_2010321_ICP3_JKB2b_TF014a_accel.txt is shown in Figure 1.
Software and Tools
No special tools are required for the ASCII text files.
Quality depends on the flight conditions for each data transect and must be assessed on a flight by flight basis. Smooth flight with small trajectory changes will produce good data.
Data Acquisition and Processing
This data set has four data types:
- Timestamps: time in UTC
- Aircraft positions: geodetic location of the reference GPS antenna
- Aircraft attitudes: three angles to describe the aircraft orientation in reference to direction North and the local vertical.
- Force on a constrained vertical sensor converted to equivalent acceleration of an unconstrained mass reported as Vertical Acceleration. Vertical Acceleration is the purpose of this data set. The other fields are auxiliary data.
A sensitive accelerometer is held vertical by a 2-axis platform which counters aircraft pitch and roll. The measured force on the accelerometer is reported as the Vertical Acceleration by the device. This is the sum of gravitational force and force due to inertial accelerations in the vertical direction.
The output of the gravimeter consists of accelerations measured in real time. These accelerations are recorded at a rate of 1 Hz by the external data recording system which time stamps the data as they are acquired and recorded.
Raw instrument outputs are recorded with timestamps then minimally processed to convert from the native instrument output format to ASCII formatted numerical values.
Trajectory and Attitude Data
Trajectory and attitude data from GPS and an IMU external to the instrument are prepended to instrument data to create the data records in these files.
The raw instrument output format is captured at 1 Hz and time stamped. The raw format is converted to ASCII numeric values and recorded. This raw numeric data consists of a value which is multiplied by a Scale Factor and added to a Bias to obtain the acceleration values in milligals, which is the value recorded in these data files. The header for each file has entries for the Scale Factor and Bias used.
The time stamps are slightly corrected by a few milliseconds to remove jitter from the acquisition system.
On 02 May, 2012, V01 2011 Antarctica data were replaced by V01.1. In V01.1, additional fields were added containing low-precision real-time position and orientation data resampled to match the times of the existing geophysical samples.
On 26 April 2013, the 2009, 2010, and 2011 Antarctica data were replaced. The format of 2009 and 2010 Antarctica data was revised to that of the 2011 Antarctica data, ensuring the time stamps are UTC year, day, and time, and adding georeferencing fields including real time position, roll, pitch and heading. For some campaigns V01.2 includes more flights than V01.1.
he 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 most of these data the instrument was well stabilized. For data from the 2010-11 season, the instrument had large issues with drift.
The precise accelerations recorded by the gravimeter are subject to degradation by aircraft maneuvering, turbulence and shocks, and to a lesser extent by smooth changes in altitude. The best results are from smooth, straight, level flight as can be determined by examination of the GPS trajectory.
Instrument name: Bell Aerospace (now Lockheed-Martin) BGM–3 number #203.
Type: Two–axis stabilized platform scalar gravimeter.
Resolution: 1 Hz in time.
References and Related Publications
Contacts and Acknowledgments
Donald D. Blankenship, Thomas G. Richter, Scott D. Kempf, Duncan A. Young
University of Texas at Austin
Institute for Geophysics
Austin, TX, 78759-8500, USA
Martin J. Siegert
University of Bristol
12 Berkeley Square University Road
BS8 1SS England
Jason L. Roberts and Tas van Ommen
Australian Antarctic Division
Kingston, Tasmania 7050, Australia
Antarctic Climate & Ecosystems Cooperative Research Centre
Hobart, Tasmania 7001, Australia
Emmanuel Le Meur
University of Grenoble Alpes, LGGE, UMR5183
38041 Grenoble, France
Note: Data file header contains personnel information for each transect.
NASA's Operation Ice Bridge (grant NNX09AR52G, contract NNG10HP06C (American Recovery and Reinvestment Act), and grant NNX11AD33G) to the University of Texas at Austin. NSF's International Polar Year activities (grant ANT-0733025) to the University of Texas at Austin, the Antarctic Ecosystems and Climate Collaborative Research Center at the University of Tasmania, and the UK's NERC grant NE/D003733/1 to University of Edinburgh. See data file header for funding information for each transect.
Document Creation Date
10 June 2014