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Citation
Blankenship, D.D., Roberts, J.L., Greenbaum, J.S., Young, D.A., Van Ommen, T., Le Meur, E., Beem, L.H. (2018, updated 2018) EAGLE/ICECAP II RADARGRAMS Australian Antarctic Data Centre - doi:10.26179/5bcff4afc287d
Title
EAGLE/ICECAP II RADARGRAMS
Data Centre
Australian Antarctic Data Centre, Australia
DOI
doi:10.26179/5bcff4afc287d
Created Date
2018-10-05
Revision Date
2018-10-05
Parent record
None

Description

These radargrams were collected as part of the ICECAP (International Collaborative Exploration of the Cryosphere through Airborne Profiling) collaboration in 2015/16 (ICP7) and 2016/17 (ICP8). These data were in part funded by the US National Science Foundation (grant PLR-1543452 to UTIG), Antarctic Gateway, ACE-CRC the G. Unger Vetlesen Foundation, and supported by the Australian Antarctic Division through project AAS-4346.

These data collection represents georeferenced, time registered instrument measurements (L1B data) converted to SI units, and is of most interest to users who wish to reprocess the data. Users interested in geophysical observables should used the derived Level 2 dataset. The data format are netCDF3 files, following the formats used for NASA/AAD/UTIG's ICECAP/OIB project at NASA's NSIDC DAAC. Metadata fields can be accessed using the open source ncdump tool, or c, python or matlab modules. See https://www.loc.gov/preservation/digital/formats/fdd/fdd000330.shtml for resources on NetCDF-3, and https://nsidc.org/data/IR2HI1B/versions/1 for a description of the similar OIB dataset.

RADAR
Ice penetrating radar provides the geometry of the ice shelves and outlet glaciers, and provides constraints on properties at the base of the ice (e.g. subglacial waters, sub ice shelf melting)
ER2HI1B georeferenced radar echo data; 4 Hz NetCDF

Data Acquisition Parameters
A 1-μsec transmitted chirp was used for both surface and bed. Two 14-bit digitizer channels with offset receiver gain were used to record returned echoes over 64 μsec, accommodating 120 dB of dynamic range, including accurate representations of power of the surface and bed echoes.

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: 64.74 μsec
Acquisition: two gain channels separated by 47 dB
Dynamic Range: 120 dB
Monostatic Rx/Tx
Data rate: 2.2 MB/sec
Maximum Doppler frequency: 36 Hz
Pulse Repetition Frequency: 6250 Hz
Onboard stacking: 32x

Processing Approach
Unfocused Synthetic aperture 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).

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Purpose

We proposed to integrate aerogeophysical data collected over three critical sections of the East Antarctic grounding zone (Totten Glacier, Denman Glacier, and Cook Ice Shelf). We are motivated by their differences in recent grounding zone altimetry records and their offshore record of Cenozoic retreat. We will assess three hypotheses to isolate the processes that drive the differences in observed grounding zone thinning: 1. Bathymetry and large-scale ocean forcing control cavity circulation; 2. ice shelf draft and basal morphology control cavity circulation; 3. Subglacial freshwater input across the grounding line controls cavity circulation.

Due to the presence of large subglacial basins under the ice sheet, the Indo-Pacific sector of the East Antarctic Ice Sheet is susceptible to ice loss through grounding line retreat. Ice shelves help prevent this retreat by exerting a buttressing effect, which is a function of the ice shelves’ thickness. However, recent airborne and satellite results have reported significant basal melting of many East Antarctic ice shelves, which decreases ice shelf thickness. As a result, lower backstress on the interior ice can potentially allow increased discharge of ice across the grounding line. For specifically these reasons, this region has been the target of ongoing United States and foreign scientific airborne and marine expeditions, as well as a major International Ocean Drilling Project effort in 2008. These studies have provided the large-scale context for the interior grounded ice and sparse continental shelf sampling which both indicate that the Indo-Pacific margin of the EAIS has advanced and retreated into the deep interior basins many times. This finding confirms the importance of better understanding of this area and its controls in order to constrain future sea level estimates. The key outcomes of our research will be: 1. An evaluation of land ice and ocean coupling in areas of significant potential sea level contribution; 2. Relating volume changes of grounded and floating ice to regional oceanic heat transport and sub-ice shelf ocean dynamics in areas of significant potential sea level and meridional overturning circulation impacts; 3. Improved boundary conditions to evaluate mass, heat, and freshwater budgets of East Antarctica’s continental margins

Quality

On ICP7 flights F03, F04, F05 and F09, the left hand radar antenna was not operational. On ICP7 flights F06, F07, F23 and F24, the radar antennas were not installed. In ICP7, there was a power mismatch between the left and right receivers. On ICP8 flights F01 to F06, the antenna beam pattern had a nadir-directed null due to a reversed balun.

Access

Owing to their size, these data are publicly available on request to the Australian Antarctic Data Centre.

Temporal Coverages

Spatial Coverages

Science Keywords

Additional Keywords

  • RADARGRAM
  • ICE PENETRATING RADAR
  • RADIO ECHO SOUNDING

Locations

  • CONTINENT > ANTARCTICA > COOK ICE SHELF
  • CONTINENT > ANTARCTICA > DENMAN GLACIER
  • CONTINENT > ANTARCTICA > GEORGE V COAST
  • CONTINENT > ANTARCTICA > KNOX COAST
  • CONTINENT > ANTARCTICA > SABRINA COAST
  • CONTINENT > ANTARCTICA > TOTTEN GLACIER
  • GEOGRAPHIC REGION > POLAR
  • OCEAN > SOUTHERN OCEAN

Platforms

  • Basler BT-67

Instruments

  • Hi-Capability Radar Sounder Version2

Researchers

  • blankenship, donald (INVESTIGATOR)
  • roberts, jason (INVESTIGATOR,TECHNICAL CONTACT)
  • greenbaum, jamin (INVESTIGATOR)
  • young, duncan (INVESTIGATOR,TECHNICAL CONTACT,DIF AUTHOR)
  • van ommen, tas (INVESTIGATOR)
  • le meur, emmanuel (INVESTIGATOR)
  • beem, lucas (INVESTIGATOR)

Use Constraints

This data set conforms to the CCBY Attribution License (http://creativecommons.org/licenses/by/4.0/).

Please follow instructions listed in the citation reference provided at http://data.aad.gov.au/aadc/metadata/citation.cfm?entry_id=AAS_4346_EAGLE_ICECAP_LEVEL2_RADAR_DATA when using these data.

Creative Commons License