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IceBridge HiCARS 1 L2 Geolocated Ice Thickness, Version 1
This data set contains ice thickness, surface and bed elevation, and echo strength measurements taken over Antarctica using the Hi-Capability Airborne Radar Sounder (HiCARS) instrument. 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.
|Data Contributor(s):||Donald Blankenship, Scott Kempf, Duncan Young, Thomas Richter, Dustin Schroeder, Jamin Greenbaum, John Holt|
|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, D. M. Schroeder, J. S. Greenbaum, J. W. Holt, T. van Ommen, R. C. Warner, J. L. Roberts, N. W. Young, E. Lemeur, and M. J. Siegert. 2011, updated 2017. IceBridge HiCARS 1 L2 Geolocated Ice Thickness, 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/F5FGUT9F5089. [Date Accessed].
Detailed Data Description
The data files are in space-delimited ASCII text format.
Data are available in the https://n5eil01u.ecs.nsidc.org/ICEBRIDGE/IR2HI2.001/ directory. Within this directory, the folders are organized by date, for example /2009.11.09/. Folders contain ASCII (.txt) and XML (.xml) files. XML files contain file level metadata and location, platform, and campaign information.
The data set files are named according to the following convention and as described in Table 1:
File name examples:
|IR1HI2||Short name for IceBridge HiCARS 1 L2 Geolocated Ice Thickness|
|YYYY||Four-digit year of survey|
|DOY||Day of year of survey|
|XXXX||Geographic track line|
|icethk||Ice thickness data|
|xxx||File type: ASCII text (.txt), or XML (.txt.xml)|
The data files range from approximately 29 KB to 5 MB.
XML files range from approximately 4 KB to 42 KB.
The data set when downloaded in its entirety is approximately 436 MB.
Spatial coverage for this data set is Antarctica, generally described in the coordinates below.
Southernmost Latitude: 90° S
Northernmost Latitude: 53° S
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E
Figure 1 illustrates specific locations for this data set.
Figure 1. Coverage in the Wilkes Land Sector of East Antarctica
Profile data in this product is sampled at 4 Hz (~23 m) along track. Due to the limited processing for this 'pik1' product, horizontal resolution is approximately 400 m, and vertical resolution is 8 m. (See the Processing Steps section below for description of 'pik1'.)
Projection and Grid Description
Referenced to WGS-84 Ellipsoid, ITRF-2008.
These data were collected as part of the five-year international ICECAP program which included four Operation IceBridge funded campaigns.
Temporal coverage for the IR1HI2 data set is 02 January 2009 to 21 December 2010.
ICECAP HiCARS 1 campaigns operated between October and February from 2008 to 2010. Typically three 7-hour flights were flown per week.
The HiCARS 1 L2 Geolocated Ice Thickness Antarctica files contain fields as described in Table 2.
|DOY||Day Of Year||UTC|
|SOD||Second Of Day||UTC|
|LON||Longitude||Decimal degrees, WGS-84|
|LAT||Latitude||Decimal degrees, WGS-84|
|THK||Radar Derived Ice Thickness using dielectric of ice of 3.15 and no firn correction||Meters|
|SRF_RNG||Radar Derived Surface Range||Meters|
|BED_ELEVATION||Radar Derived Bed Elevation||Meters, WGS-84|
|SURFACE_ELEVATION||Radar Derived Surface Elevation||Meters, WGS-84|
|PARTIAL_BED_REFLECT||Bed reflection coefficient @ 60 MHz||Decibels with reference to perfect reflector; no ice loss accounting|
|SRF_REFLECT||Surface reflection coefficient @ 60 MHz||Decibels with reference to perfect reflector|
|AIRCRAFT_ROLL||Roll, right wing down positive||Degrees|
Horizontal positions represent aircraft location at the time of the observation.
Radar Derived Surface Elevations should not be used for quantitative surface elevation analysis. Use of the laser-derived products is recommended for surface elevation analysis.
Do not directly sum or average records in Decibels. Convert Decibels to linear power (10(dB/10)) first.
Locations are indicated by a surface elevation with no corresponding surface reflectivity.
Sample Data Record
Shown below are the first eleven data records from data file: IR1HI2_2010351_ASB_JKB1a_R04Wb_icethk.txt.
Software and Tools
The data files may be opened by any ASCII text reader.
Data Acquisition and Processing
A 1-μsec transmitted chirp was used for both surface and bed. Two 12-bit digitizer channels with offset receiver gain were used to record returned echoes over 64 μsec, accommodating 120 dB of dynamic range, including the surface and the bed.
Bandwidth: 52.5-67.5 MHz
Tx power: 5700 W
Waveform: 1 μsec FM chirp generation, analog down-conversion to 10 MHz center
Sampling: 12-bit ADC at 50 MHz sampling
Record window: 64 μsec
Acquisition: two gain channels separated by 39 dB (28 dB for 2009-10)
Dynamic Range: 120 dB
Data rate: 2.2 MB/sec
Maximum Doppler frequency: 36 Hz
Pulse Repetition Frequency: 6400 Hz
Onboard stacking: 32x
Radar equation used (surface):
Surface reflectivity coefficienty = Power[received]/(Power[transmitted]*Antenna_gain*wavelength[air]2)/(((4*pi)2)*(2*range)2).
Ice thicknesses were estimated from the two-way travel time between the surface and the bed using 3.15 as the dielectric constant for ice and no firn correction.
Trajectory and Attitude Data
Please see the IceBridge GPS/IMU L1B Primary Position and Attitude Solution (IPUTG1B) dataset for information on positioning.
The radar data was processed using the 'pik1' processor. No focusing or range migration was performed. The original pulse repetition frequency was 6400 Hz. Echoes were summed onboard to a rate of 200 Hz. Post collection, traces were coherently summed by a factor of 10 to yield a short approximately 1 meter aperture. This short aperture suppressed surface clutter, while retaining subsurface energy.
The summed traces were pulse compressed using a 1-μsec, 15 MHz synthetic FM chirp windowed with a Hanning filter and a monochromatic local oscillator signal was filtered out at this stage. The result was converted to amplitude and was further incoherently averaged to 4 Hz, yielding 1 trace every 20 meters at typical aircraft speeds. The data was logarithmically scaled for interpretation.
The first bed and surface returns were manually bound and within each bound an algorithm detected the time delay of the brightest return for each trace. Bounds were not forced to match at cross over points, so as to preserve the validity of statistics for the bed returns between cross overs.
On July 23, 2012, Version 01 2009 Antarctica data were replaced by Version 01.1. The V01.1 2009 Antarctica data are re-organized, and include aircraft orientation and surface and bed reflection coefficient information not contained in the V01 data.
On 08 July 2013, the 2009 Antarctica data were replaced with V01.2. In V01.2, data fields are re-ordered and revised.
On 13 March 2017, the entire IR1HI2 data set was replaced with V01.3 data. V01.3 data files include extensive header information, including field descriptions, campaign information, and data processing notes. XML metadata files were also added to the V01.3 data set. XML files contain file level metadata and location, platform, and campaign information.
In Antarctica 2009 toward the end of the season (during the NWZ and ICG1 projects) the radar developed timing instabilities consistent with an overloaded CPU.
In Antarctica 2009 during the NWZ, MZG, and ALG2 projects and part of the ASB project, the radar was co-operated with the 2 MHZ JPL WISE radar. As the two systems were not synchronized, elevated noise floors are apparent in both systems.
In Antarctica 2010, HiCARS 1 suffered a catastrophic transmitter failure on 1CP3/F15 (J322/2010, 18 November 2010) which was not repaired until ICP3/F18 (J329/2010, 25 November 2010).
HiCARS 1 bed data take the range to the bed echo and converts that to an apparent nadir ice thickness. However, the first unfocused echo may actually arrive from up to 700 m around the nadir spot, depending on ice thickness, aircraft height above the ice, and bed roughness. For extreme cases, this could result in errors in actual ice thickness of 70 meters, and a horizontal error of 700 m. Generally nadir ice thicknesses will be biased low in pik1 data, and actual ice thicknesses based on the first return biased high.
The High Capability Radar Sounder (HiCARS) is a VHF ice-penetrating radar which operates in frequency-chirped mode from 52.5 to 67.5 MHz. HiCARS allows for phase coherent recording of radar returns for advanced processing. For antennas the system uses twin flat dipoles, one mounted under each aircraft wing providing approximately 10 dB of antenna gain. The antennas are mounted 19 meters apart horizontally (Peters et al. 2005; Peters et al. 2007; Young et al. 2015).
The HiCARS 1 3-stage transmitter was constructed by the Technical University of Denmark in 1975 for the joint NSF-SPRI-TUD (Scott Polar Research Institute - Technical University of Denmark) aerogeophysics program (Drewry et al., 1978; Skou and Søndergaard, 1976). A 25 W preamp fed a 500 W Primary Pulsed Amplifier (PPA) which supplied a 5700 W High Power Pulsed Amplifier (HPPA). Power was transmitted through a TUD passive Transmit-Receive switch. For the 2009 season onward, the preamp/PPA was replaced by a 1000 W Tomco Technologies BT1000-Gamma4T.
The HiCARS 1 receivers and signal generators were built by the Jet Propulsion Laboratory as part of a Europa test bed program (Moussessian et al., 2001). For the same program, the University of Kansas developed digitizers and the acquisition computer.
In Antarctica 2010, HiCARS 1 was replaced with the lighter, off the shelf HiCARS 2 radar system (See IceBridge HiCARS 2 L2 Geolocated Ice Thickness (IR2HI2)). HiCARS 1 was retired after flight ICP3/F36 (J363/2010, 29 December 2010).
References and Related Publications
Contacts and Acknowledgments
Blankenship, Donald D., Duncan A. Young, Scott D. Kempf, Thomas G. Richter, Dustin M. Schroeder, Jamin S. Greenbaum and John. W. Holt
University of Texas at Austin
Institute for Geophysics
Austin, TX, 78759-8500
Martin J. Siegert
Grantham Institute, and Department of Earth Sciences and Engineering
Imperial College London
London SW7 2AZ, UK
Jason L. Roberts, Roland C. Warner, Neal W. Young and Tas van Ommen
Australian Antarctic Division
Kingston, Tasmania, Australia
Antarctic Climate and Ecosystems Cooperative Research Centre
University of Tasmania
Hobart, Tasmania, Australia
University of Grenoble Alpes
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
The collection of this data was funded by a variety of sources, including NASA's Operation Ice Bridge (grants NNX09AR52G, NNG10HP06C and NNX11AD33G) and National Science Foundation grant PLR-0733025 to the University of Texas at Austin, the United Kingdom's National Environmental Research Council grant NE/F016646/1, and Australia's Antarctic Climate and Ecosystems Collaborative Research Center. Logistical support was provided by the United States Antarctic Program, the Australian Antarctic Program (through projects 3103 and 4077), the French Polar Institute and Italy's Programma Nazionale Di Ricerche In Antartide. Full funding information for each line can be found in the file header.
2008 campaign data were acquired pre-IceBridge.
DOCUMENT CREATION DATE
14 March 2017