Data Set ID: 
IR1HI1B

IceBridge HiCARS 1 L1B Time-Tagged Echo Strength Profiles, Version 1

This data set contains Antarctica radar sounder echo strength profiles from the Hi-Capability Radar Sounder (HiCARS) Version 1 instrument. The data were collected by scientists working on the Investigating the Cryospheric Evolution of the Central Antarctic Plate (ICECAP) project, which was funded by the National Science Foundation (NSF) and the Natural Environment Research Council (NERC) with additional support from NASA Operation IceBridge.

This is the most recent version of these data.

Version Summary: 

Initial release

BASIC Level of Service

Data: Data integrity verified

Documentation: Key metadata and links to supporting documentation available

User Support: Assistance with data access and basic data usage

See All Level of Service Details

Parameter(s):
  • RADAR > RETURN POWER > PHASE AND AMPLITUDE
  • RADAR > RETURN POWER
Data Format(s):
  • NetCDF
  • PDF
Spatial Coverage:
N: -53, 
S: -90, 
E: 180, 
W: -180
Platform(s):BT-67, DHC-6
Spatial Resolution:
  • Varies x Varies
Sensor(s):HiCARS1
Temporal Coverage:
  • 2 January 2009 to 29 December 2010
Version(s):V1
Temporal Resolution1 yearMetadata XML:View Metadata Record
Data Contributor(s):Donald Blankenship, Scott Kempf, Duncan Young, Thomas Richter, Dustin Schroeder, Jamin Greenbaum, Gregory Ng, Tas van Ommen, Roland Warner

Geographic Coverage

Other Access Options

Other Access Options

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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., S. D. Kempf, D. A. Young, T. G. Richter, D. M. Schroeder, J. S. Greenbaum, T. van Ommen, R. C. Warner, J. L. Roberts, N. W. Young, E. Lemeur, M. J. Siegert, and J. W. Holt. 2017. IceBridge HiCARS 1 L1B Time-Tagged Echo Strength Profiles, 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/W2KXX0MYNJ9G. [Date Accessed].

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Detailed Data Description

Format

The data files are in NetCDF (.nc) format.

Each data file is paired with an associated XML file (.xml).

Browse files are provided in PDF format (.pdf).

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File Naming Convention

The data set files are named according to the following convention and as described in Table 1:

File name examples:

IR1HI1B_2010342_WSB_JKB1a_GL0143a_003.nc
IR1HI1B_2010342_WSB_JKB1a_GL0143a_003.nc.xml
IR1HI1B_2010342_WSB_JKB1a_GL0143a_003.nc.browse.pdf

IR1HI1B_YYYYDOY_AAAA_JKB2x_TTTT_nnn.xxx

Where:

Variable Description
Table 1. File Naming Convention
IR1HI1B Short name for IceBridge HiCARS 1 L1B Time-Tagged Echo Strength Profiles
YYYY Four-digit year of survey
DOY Three digit day of year of survey
AAAA Geographic area
JKB2x Host platform name
TTTT Geographic track line, transect name within project
nnn Granule within line
.xxx File type: NetCDF (.nc), XML (.nc.xml), or PDF browse (.nc.browse.pdf)
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File Size

The NetCDF data files range from approximately 595 KB to 98 MB.

The XML data files range from approximately 4 KB to 34 KB.

The PDF browse files range from approximately 36 KB to 2 MB.

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Volume

The full data set is approximately 112 GB.

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Spatial Coverage

The target region for this data is Antarctica. Please see XML metadata files for targets for each granule.

Antarctica:
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

Spatial Resolution

Processed radar soundings are given every 4 Hz (250 milliseconds) which is roughly 20 m apart depending on platform velocity. Vertical samples (fast time) are given at 50 MHz (20 ns fast time). This is approximately 3 meters in air and 1.7 meters in ice.

Projection and Grid Description

Latitude, longitude, and altitude are provided using the WGS84 reference, ITRF-2008. Flight tracks are generally straight lines in the polar stereographic projection using a true scale latitude of 71 degrees south.

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Temporal Coverage

These data were collected as part of Investigating the Cryospheric Evolution of the Central Antarctic Plate (ICECAP), National Science Foundation (NSF), National Environmental Research Council (NERC), and Operation IceBridge funded campaigns from 02 January 2009 to 29 December 2010.

Temporal Resolution

ICECAP campaigns were conducted on an annual basis. East Antarctic campaigns for this data set typically extend from November to early January.

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Parameter or Variable

Parameter Description

The HiCARS 1 L1B Time-Tagged Echo Strength Profiles data files contain fields as described in Table 2.

Parameter Description Units
Table 2. File Parameter Description
time Time of day, seconds since 2009-01-02 00:00:00 UTC
fasttime 2-way travel time Microseconds
lat Latitude of sample Decimal degrees North, WGS-84
lon Longitude of sample Decimal degrees East, WGS-84
altitude Altitude of antenna above nominal sea level (WGS84) Meters
pitch Pitch of the JKB platform.  Positive is nose up.  Zero is horizontal. Degrees
roll Roll of the JKB platform.  Positive is right wing up.  Zero is horizontal. Degrees
heading Heading of the JKB platform.  Positive is clockwise from above.  Zero is true north. Degrees
amplitude_low_gain Amplitude of low gain radar reflection after processing Counts in dBV
ampltude_high_gain Amplitude of high gain radar reflection after processing Counts in dBV

Sample Data Record

Below are amplitude values from a sample of the IR1HI1B_2010342_WSB_JKB1a_GL0143a_003.nc data file as displayed in the HDFView tool.

sample data

Figure 2. Sample Data showing amplitude values

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Software and Tools

The following links provide access to software for reading and viewing NetCDF data files. Please be sure to review instructions on installing and running the programs.

XML files can be read with browsers such as Firefox and Internet Explorer.

PDF browse files can be displayed by any software capable of reading PDF format.

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Data Acquisition and Processing

Theory of Measurements

Ice is nearly transparent at Very High Frequency (VHF) radio frequencies (Dowdeswell and Evans, 2004). Radar operates by transmitting a radio frequency signal and receiving the power, phase, and time delay of the returning echo. For airborne sounding of ice, antennas direct energy to nadir, and through repeated pulses and motion of the aircraft, a radargram (a profile of power in time delay versus transmit time coordinates) can be mapped out. From the time delay between transmission and reception, and knowledge of the refractive index of ice, range to the bed can be estimated. The phase history of a given point can be used to focus the along track position of a specific point, or filter out off-nadir scattering that can obscure the bed. The power of reflection relates to the dielectric contrasts between media and the roughness of the interface.

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Data Acquisition Methods

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
Monostatic Rx/Tx
Data rate: 2.2 MB/sec
Maximum Doppler frequency: 36 Hz
Pulse Repetition Frequency: 6400 Hz
Onboard stacking: 32x

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Trajectory and Attitude Data

Please see the IceBridge GPS/IMU L1B Primary Position and Attitude Solution (IPUTG1B) data set for information on positioning.

Processing Steps

Unfocussed Synthetic Aperture r=Radar (SAR) processing was done (internally referred to as pik1). This is a quick form of processing with no dependencies on other instruments. The first 10 recorded stacks are coherently summed resulting in a 20 Hz sample rate. Then, a narrow band notch filter is applied at 10 MHz to remove local oscillator (LO) leakage. The pulse is compressed using frequency domain convolution of over-scaled synthetic chirp waveform. This results in gains of 83 dB from overscaled chirp, 11.7 dB from range compression, and -3 dB from Hanning window. These are converted to magnitude and five of these stacks are incoherently summed resulting in the final 4 Hz sample rate.

Error Sources

For this Level 1B product, errors in power may be due to transmitter or receiver malfunctions. Elevated background noise may occur with areas of strong surface scattering (for example crevasses) or Radio Frequency (RF) noise from anthropogenic sources (for example radio calls from the aircraft or other radar systems).

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.

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Sensor or Instrument Description

The High Capability Radar Sounder (HiCARS) is a VHF ice-penetrating radar that 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.

The HiCARS components were integrated and configured for Antarctic operations during the 2001 Antarctic field season (Peters et al. 2005; Peters et al. 2007).

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).

Processing Method

During acquisition, the 12-bit samples at the same time delay are added together 32 times.

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References and Related Publications

Contacts and Acknowledgments

Blankenship, Donald D., Duncan A. Young, Scott D. Kempf, Thomas G. Richter, Jamin S. Greenbaum and John. W. Holt
University of Texas at Austin
Institute for Geophysics
Austin, TX, 78759-8500

Dustin M. Schroeder
Stanford University
450 Serra Mall
Stanford, CA 94305

Martin J. Siegert
Grantham Institute, and Department of Earth Sciences and Engineering
Imperial College London
South Kensington
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

Emmanuel LeMeur
University of Grenoble Alpes
LGGE
Grenoble, France

Technical Contact

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
e-mail: nsidc@nsidc.org

Acknowledgments: 

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.

Document Information

DOCUMENT CREATION DATE

12 July 2017

DOCUMENT REVISION DATE

No technical references available for this data set.

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