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.
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.
We kindly request that you cite the use of this data set in a publication using the following citation. For more information, see our Use and Copyright Web page.
Blankenship, Donald D., Thomas G. Richter, and Duncan Young. 2012, updated 2013. IceBridge ZLS Dynamic Gravity Meter Time-Registered L1B Vertical Accelerations. [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. http://nsidc.org/data/igzls1b.html.
ZLS Dynamic Gravity Meter
5 to 10 km
29 November 2011 to 21 December 2011
November and December 2011
ASCII text (.txt)
Donald D. Blankenship, Thomas G. Richter, Duncan Young
University of Texas at Austin
Institute for Geophysics
Austin, TX, 78759-8500
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
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.
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.
Data are available on the FTP site in the ftp://n5eil01u.ecs.nsidc.org/SAN2/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.
The files are named according to the following convention and as described in Table 1:
|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|
|xxx||Indicates ASCII text file .txt, or or XML file .xml|
The ASCII data files range from approximately 46 KB to 1.7 MB.
The XML files range from approximately 10 KB to 35 KB.
The entire data set is approximately 29 MB.
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
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.
These data were collected as part of ICECAP, NSF, NERC, and Operation IceBridge funded campaigns from 29 November 2011 to 21 December 2011.
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.
The data files contain fields as described in Table 2.
|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
Shown below are the first five records from the data file: IGZLS1B_2011354_ICP4_JKB5c_F22T02a_accel.txt
Figure 1. Sample Data Record
Data are available via FTP.
No special tools are required for the ASCII text files.
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.
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.
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 from GPS and an IMU external to the instrument are prepended to instrument data to create the data records in these files.
No processing was done on the instrument output.
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.
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.
These data sets should be capable of providing gravity field data accurate to a few milligals during the periods of smooth aircraft flight, with post-processing standard for geophysical gravity. The related data collections listed below provide complementary measurements taken on the same flights as these.
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.
UltraSys User's Guide, ZLS Corporation, Rev: 3.09.1 2011/03/18
Vallient, H. D. 1992, The LaCoste & Romberg Air/Sea Gravity Meter: An Overview, in CRC Handbook of Geophysical Exploration at Sea: Hydrocarbons, edited by R. A. Geyer, 2nd ed., chap. 7:141-176.
The acronyms used in this document are listed in Table 3.
|ASCII||American Standard Code for Information Interchange|
|BAS||British Antarctic Survey|
|CIRES||Cooperative Institute for Research in Environmental Science|
|FTP||File Transfer Protocol|
|ICECAP||Investigating the Cryospheric Evolution of the Central Antarctic Plate|
|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|
25 February 2015