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This data set contains vertical, cross body, and along body acceleration values for geophysical survey flights in Antarctica using the ZLS Dynamic Gravity Meter. The data were collected by scientists working on the International Collaborative Exploration of the Cryosphere through Airborne Profiling (ICECAP) project, which was funded by the National Science Foundation (NSF), the Antarctic Climate and Ecosystems Collaborative Research Center, and the Natural Environment Research Council (NERC) with additional support from NASA Operation IceBridge.
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Data Set ID:
IGZLS1B
IceBridge ZLS Dynamic Gravity Meter Time-Registered L1B Vertical Accelerations, Version 1
This is the most recent version of these data.
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Geographic Coverage |
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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., D. A. Young, and T. G. Richter. 2012, updated 2013. IceBridge ZLS Dynamic Gravity Meter Time-Registered L1B Vertical Accelerations, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/XASIHXV1V5B5. [Date Accessed].Collapse All / Open All
Detailed Data Description
Format
The data files are in space-delimited ASCII text format. Each data file is paired with an associated XML file. The XML files contain location, platform, and instrument metadata.
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File and Directory Structure
Data are available in the https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/IGZLS1B.001/ directory. Within this directory, the folders are organized by date, for example /2011.11.29/ to /2011.12.21/. Folders contain ASCII (.txt) and XML (.xml) files.
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File Naming Convention
The files are named according to the following convention and as described in Table 1:
IGZLS1B_2011354_ICP4_JKB5c_F22T02a_accel.txt
IGZLS1B_2011354_ICP4_JKB5c_F22T02a_accel.txt.xml
IGZLS1B_YYYYDOY_PPP_JKB5c_TTTT_accel.xxx
Where:
| Variable | Description |
|---|---|
IGZLS1B |
Short name for IceBridge ZLS Dynamic Gravity Meter Time-Registered L1B Vertical Accelerations |
YYYY |
Four-digit year of survey |
DOY |
Day of year of survey |
PPP |
Geographic area (Project) |
JKB5c |
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
The ASCII data files range from approximately 46 KB to 1.7 MB.
The XML files range from approximately 10 KB to 35 KB.
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Volume
The entire data set is approximately 29 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
The instrument data rate of 1 Hz produced a data packet of approximately 90 m each during flight for the raw data set. However, filtering during post processing will result in an effective resolution in the final result of 5 to 10 km.
Projection and Grid Description
WGS-84
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Temporal Coverage
These data were collected as part of ICECAP, NSF, NERC, and Operation IceBridge funded campaigns from 29 November 2011 to 21 December 2011.
Temporal Resolution
This data set was collected during the November/December 2011 season of ICECAP/IceBridge. Similar data was collected by other instruments during other expeditions but this was a one-season use for this type instrument and these projects.
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Parameter or Variable
Parameter Description
The data files contain fields as described in Table 2.
| 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 (with respect to north) | Degrees |
| Vertical acceleration - 60 second RC filter for QC only | milliGals |
| Spring tension- proportional to course gravity | counter units |
| Beam position (beam velocity is proportional to high frequency gravity) | milliVolts |
| Cross coupling - accounts for transfer of sensor dynamics to gravity signal | milliVolts |
| Cross body acceleration from platform accelerometers | milliGals using 25.8 scaling from mV |
| Along body acceleration from platform accelerometers | milliGals using 26.2 scaling from mV |
| XACC2 cross coupling due to platform leveling errors: Cross body acceleration2 | milliVolts2 |
| LACC2 cross coupling due to platform leveling errors: Along body acceleration2 | milliVolts2 |
| VE cross coupling due to damping non-linearity: Beam velocity2 | milliVolts2 |
| VCC cross coupling due to inherent cross coupling: along body acceleration * beam position | milliVolts |
| AX cross coupling due to imperfect coupling: cross body acceleration * beam velocity | milliVolts |
| AL cross coupling due to imperfect coupling: along body acceleration * beam velocity | milliVolts |
| AX2 cross coupling due to 2nd order imperfect coupling: cross body acceleration2 * beam velocity | milliVolts |
| Index for platform period (1=16 minutes; 25=4 minutes; 100=2 minutes) | minutes |
Note: Positions are interpolated from the real time GPS feed and have an accuracy of several meters
Sample Data Record
Shown below are the first five records from the data file: IGZLS1B_2011354_ICP4_JKB5c_F22T02a_accel.txt
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Software and Tools
No special tools are required for the ASCII text files.
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Data Acquisition and Processing
Theory of Measurements
The ZLS Dynamic Gravimeter used for this data set uses a proof mass (beam) suspended by a highly damped mechanical spring as the sensitive vertical acceleration sensor mounted aboard a two axis gyroscopically stabilized platform. Accelerations of the mass are measured via monitoring of spring tension and beam velocity. Further description of this instrument is available in Vallient 1992.
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Data Acquisition Methods
The ZLS instrument was installed and operated according to the instrument manuals. The instrument real time (ASCII) data output was recorded to a central data acquisition system (JKB5c) which provided GPS referenced time stamps for each data packet. This was separate from the acquisition system (JKB2e) used for most other instruments during the 2011 field season.
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Derivation Techniques and Algorithms
Raw instrument outputs are recorded with timestamps. Externally provided position and attitude data was prepended to each data packet. No further processing was performed on these data.
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.
Processing Steps
No processing was done on the instrument output.
Version History
On 01 May 2013, V01 2011 Antarctica data were replaced by V01.1. In V01.1, additional fields were added containing real-time position and orientation data. V01.1 does not include data for 15 December 2011 and 20 December 2011.
Error Sources
Data quality is degraded by aircraft maneuvers beyond straight and level flight. Data in actual aircraft turns is unusable.
This data set contains instances where the Spring Tension (entry 12 in the data packet) was incorrectly recorded by the instrument, leading to significant biases, but no higher frequency errors, in the calculated instrument acceleration unless corrected in post processing. These instances are randomly distributed in the data.
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Sensor or Instrument Description
The instrument used was the ZLS Dynamic Gravimeter serial number S-83 with the UltraSys control system. This is based on the LaCoste and Romberg Air/Sea Gravity Meter with a control system upgrade. The system was loaned to the ICECAP project by the British Antarctic Survey (BAS) as a backup to the primary BGM-3 gravity meter for the 2011 field season. As adequate gravity data was obtained from the BGM-3 (see IGBGM1B and IGBGM2), no Level-2 ZLS gravity data has been generated from the IGZLS1B data set. Gravity data from this sensor has been released for BAS field seasons, and can be found at https://secure.antarctica.ac.uk/data/aerogeo/index.php.
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References and Related Publications
Contacts and Acknowledgments
Donald D. Blankenship, Thomas G. Richter, Duncan Young
University of Texas at Austin
Institute for Geophysics
Austin, TX, 78759-8500
Acknowledgments:
Support: NASA ICEBRIDGE (NNX11AD33G); AAD Project 3103; ICEGRAV. Funding: NASA's Operation Ice Bridge (grant NNX11AD33G) to the University of Texas at Austin. The ZLS gravity meter was provided on loan by the British Antarctic Survey.
Document Information
Document Creation Date
25 February 2015
No technical references available for this data set.
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