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Data Set ID:
IGZLS1B

IceBridge ZLS Dynamic Gravity Meter Time-Registered L1B Vertical Accelerations, Version 1

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.

Geographic Coverage

Parameter(s):
  • Geodetics/Gravity > Gravity
Spatial Coverage:
  • N: -53, S: -90, E: 180, W: -180

Spatial Resolution:
  • Varies x Varies
Temporal Coverage:
  • 29 November 2011 to 21 December 2011
(updated 2013)
Temporal Resolution: Varies
Data Format(s):
  • ASCII Text
Platform(s) BT-67
Sensor(s): ZLS
Version: V1
Data Contributor(s): Donald Blankenship, Duncan Young, Thomas Richter
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., 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: http://dx.doi.org/10.5067/XASIHXV1V5B5. [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. 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:

Table 1. Naming Convention
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.

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 (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

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.

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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

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