scholarly journals Ross Ice Shelf (Antarctica) in situ radio-frequency attenuation

2011 ◽  
Vol 57 (201) ◽  
pp. 61-66 ◽  
Author(s):  
Taylor Barrella ◽  
Steven Barwick ◽  
David Saltzberg
Keyword(s):  
Radio Frequency ◽  
Specular Reflection ◽  
Round Trip ◽  
Attenuation Length ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Trip Distance ◽  
Radio Frequency Signals ◽  
Average Electric Field

AbstractWe have measured the in situ average electric field attenuation length, 〈Lα〉, for radio-frequency signals broadcast vertically through the Ross Ice Shelf, Antarctica. We chose a location, Moore Embayment, south of Minna Bluff, known for its high reflectivity at the ice–sea interface. We confirmed specular reflection and used the return pulses to measure the average attenuation length from 75–1250 MHz over the round-trip distance of 1155 m. We find 〈Lα〉 to vary from ∼500 m at 75 MHz to ∼300 m at 1250 MHz, with an experimental uncertainty of 55–15 m.

scholarly journals South Polar in situ radio-frequency ice attenuation

2005 ◽  
Vol 51 (173) ◽  
pp. 231-238 ◽  
Author(s):  
S. Barwick ◽  
D. Besson ◽  
P. Gorham ◽  
D. Saltzberg
Keyword(s):  
Electric Field ◽  
Radio Frequency ◽  
Signal Amplitude ◽  
Attenuation Length ◽  
Polar Ice ◽  
Order Of Magnitude ◽  
Radio Frequency Signals ◽  
South Polar

AbstractWe have determined the in situ electric field attenuation length Lα (defined as the length over which the signal amplitude diminishes by a factor 1/e) for radio-frequency signals broadcast vertically through South Polar ice and reflected off the underlying bed. Conservatively assuming a bedrock field reflectivity for f = 380 MHz, and T = –50°C; the errors incorporate uncertainties in R. This value is consistent with previous estimates that the radiofrequency attenuation length exceeds the attenuation length at optical frequencies by an order of magnitude.

scholarly journals An in situ measurement of the radio-frequency attenuation in ice at Summit Station, Greenland

2015 ◽  
Vol 61 (229) ◽  
pp. 1005-1011 ◽  
Author(s):  
Jessica Avva ◽  
John M. Kovac ◽  
Christian Miki ◽  
David Saltzberg ◽  
Abigail G. Vieregg
Keyword(s):  
Radio Frequency ◽  
High Energy ◽  
In Situ Measurement ◽  
Ultra High Energy ◽  
Attenuation Length ◽  
Neutrino Detection ◽  
Dielectric Media ◽  
Ground Bounce ◽  
Radio Frequency Signals

AbstractWe report an in situ measurement of the electric field attenuation length Lα at radio frequencies for the bulk ice at Summit Station, Greenland, made by broadcasting radio-frequency signals vertically through the ice and measuring the relative power in the return ground bounce signal. We find the depth-averaged field attenuation length to be at 75 MHz. While this measurement has clear radioglaciological applications, the radio clarity of the ice also has implications for the detection of ultra-high energy (UHE) astrophysical particles via their radio emission in dielectric media such as ice. Assuming a reliable extrapolation to higher frequencies, the measured attenuation length at Summit Station is comparable to previously measured radio-frequency attenuation lengths at candidate particle detector sites around the world, and strengthens the case for Summit Station as a promising northern site for UHE neutrino detection.

New determinations of tides on the north-western Ross Ice Shelf

2020 ◽  
pp. 1-14
Author(s):  
Richard D. Ray ◽  
Kristine M. Larson ◽  
Bruce J. Haines
Keyword(s):  
Time Series ◽  
Tide Gauge ◽  
High Rate ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Global Positioning ◽  
North Western

Abstract New determinations of ocean tides are extracted from high-rate Global Positioning System (GPS) solutions at nine stations sitting on the Ross Ice Shelf. Five are multi-year time series. Three older time series are only 2–3 weeks long. These are not ideal, but they are still useful because they provide the only in situ tide observations in that sector of the ice shelf. The long tide-gauge observations from Scott Base and Cape Roberts are also reanalysed. They allow determination of some previously neglected tidal phenomena in this region, such as third-degree tides, and they provide context for analysis of the shorter datasets. The semidiurnal tides are small at all sites, yet M2 undergoes a clear seasonal cycle, which was first noted by Sir George Darwin while studying measurements from the Discovery expedition. Darwin saw a much larger modulation than we observe, and we consider possible explanations - instrumental or climatic - for this difference.

scholarly journals Snow on the Ross Ice Shelf: comparison of reanalyses and observations from automatic weather stations

2013 ◽  
Vol 7 (5) ◽  
pp. 1399-1410 ◽  
Author(s):  
L. Cohen ◽  
S. Dean
Keyword(s):  
Statistical Evaluation ◽  
Snow Accumulation ◽  
High Temporal Resolution ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
In Situ Observations ◽  
Weather Stations ◽  
Event Based ◽  
Precipitation Events

Abstract. Snow accumulation measurements from automatic weather stations (AWS) around the Ross Ice Shelf (RIS), Antarctica, are used to provide a new set of ground-based observations which are compared to precipitation from the ECMWF ERA-Interim and NCEP/NCAR Reanalysis-2 datasets. The high temporal resolution of the AWS snow accumulation measurements allow for an event-based comparison of reanalyses precipitation to the in situ observations. Snow accumulation records from nine AWS provide multiple years of accumulation data between 2008 and 2012 over a relatively large, homogeneous region of Antarctica, and also provide the basis for a statistical evaluation of accumulation and precipitation events. The complex effects of wind on snow accumulation (which can both limit and enhance accumulation) complicate the use of the accumulation measurements, but this analysis shows that they can provide a valuable source of ground-based observations for comparisons to modelled precipitation on synoptic timescales. The analysis shows that ERA-Interim reproduces more precipitation events than NCEP-2, and these events correspond to an average 8.2% more precipitation. Significant correlations between reanalyses and AWS event sizes are seen at several stations and show that ERA-Interim consistently produces larger precipitation events than NCEP-2.

scholarly journals The grounding zone of the Ross Ice Shelf, West Antarctica, from ice-penetrating radar

2011 ◽  
Vol 57 (205) ◽  
pp. 917-928 ◽  
Author(s):  
Joseph A. MacGregor ◽  
Sridhar Anandakrishnan ◽  
Ginny A. Catania ◽  
Dale P. Winebrenner
Keyword(s):  
Satellite Altimetry ◽  
In Situ Measurements ◽  
Airborne Radar ◽  
Ice Accretion ◽  
West Antarctica ◽  
Ice Shelf ◽  
Ice Streams ◽  
Ross Ice Shelf ◽  
Persistent Layer

AbstractAs ice streams flow into the Ross Ice Shelf, West Antarctica, their bed coupling transitions from weak to transient to zero as the ice goes afloat. Here we explore the nature of the bed across these crucial grounding zones using ice-penetrating radar. We collected several ground-based 2 MHz radar transects across the grounding zones of Whillans and Kamb Ice Streams and inferred bed-reflectivity changes from in situ measurements of depth-averaged dielectric attenuation, made possible by the observation of both primary and multiple bed echoes. We find no significant change in the bed reflectivity across either grounding zone. Combined with reflectivity modeling, this observation suggests that a persistent layer of subglacial water (>∼0.2 m) is widespread several kilometers upstream of the grounding zone. Our results are consistent with previous inferences of gradual grounding zones across this sector of the Ross Ice Shelf from airborne radar and satellite altimetry. Separately, the only clear bed-reflectivity change that we observed occurs ∼40 km downstream of the Kamb Ice Stream grounding zone, which we attribute to the onset of marine ice accretion onto the base of the ice shelf. This onset is much nearer to the grounding zone than previously predicted.

scholarly journals Dielectric Permittivity of Glacier Ice Measured In Situ by Radar Wide-Angle Reflection

1978 ◽  
Vol 21 (85) ◽  
pp. 315-329 ◽  
Author(s):  
Kenneth C. Jezek ◽  
John W. Clough ◽  
Charles R. Bentley ◽  
Sion Shabtaie
Keyword(s):  
Physical Phenomenon ◽  
Ice Core ◽  
Wide Angle ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Satisfactory Model ◽  
Glacier Ice ◽  
Path Geometry ◽  
Ray Path

AbstractValues of relative permittivity measured by the wide-angle reflection technique on the Ross ice Shelf show substantial variations between sites, from 3.09 to 2.89, with estimated errors of ±0.03. The largest values, closest to those normally measured in the laboratory, are found nearest to the grounded ice sheet; values decrease generally in the direction of thinner ice that has been longer on the ice shelf. We believe the variation reflects some real physical phenomenon in the ice shelf, either a true variation in the permittivity of the ice or a complication of the ray-path geometry, but are not able to offer a satisfactory model at present. We hope an explanation will be forthcoming when actual ice core samples from the deep shelf ice are available for examination.

scholarly journals Dielectric Permittivity of Glacier Ice Measured In Situ by Radar Wide-Angle Reflection

1978 ◽  
Vol 21 (85) ◽  
pp. 315-329 ◽  
Author(s):  
Kenneth C. Jezek ◽  
John W. Clough ◽  
Charles R. Bentley ◽  
Sion Shabtaie
Keyword(s):  
Physical Phenomenon ◽  
Ice Core ◽  
Wide Angle ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Satisfactory Model ◽  
Glacier Ice ◽  
Path Geometry ◽  
Ray Path

Abstract Values of relative permittivity measured by the wide-angle reflection technique on the Ross ice Shelf show substantial variations between sites, from 3.09 to 2.89, with estimated errors of ±0.03. The largest values, closest to those normally measured in the laboratory, are found nearest to the grounded ice sheet; values decrease generally in the direction of thinner ice that has been longer on the ice shelf. We believe the variation reflects some real physical phenomenon in the ice shelf, either a true variation in the permittivity of the ice or a complication of the ray-path geometry, but are not able to offer a satisfactory model at present. We hope an explanation will be forthcoming when actual ice core samples from the deep shelf ice are available for examination.

scholarly journals Radar absorption, basal reflection, thickness and polarization measurements from the Ross Ice Shelf, Antarctica

2015 ◽  
Vol 61 (227) ◽  
pp. 438-446 ◽  
Author(s):  
Jordan C. Hanson ◽  
Steven W. Barwick ◽  
Eric C. Berg ◽  
Dave Z. Besson ◽  
Thorin J. Duffin ◽  
...  
Keyword(s):  
Reflection Coefficient ◽  
Reflection Loss ◽  
High Energy ◽  
Attenuation Length ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Basal Reflection ◽  
Reflected Power ◽  
Antenna Polarization ◽  
Radio Frequency Pulses

AbstractRadio-glaciological parameters from the Moore’s Bay region of the Ross Ice Shelf, Antarctica, have been measured. The thickness of the ice shelf in Moore’s Bay was measured from reflection times of radio-frequency pulses propagating vertically through the shelf and reflecting from the ocean, and is found to be 576 ± 8 m. Introducing a baseline of 543 ± 7m between radio transmitter and receiver allowed the computation of the basal reflection coefficient, R, separately from englacial loss. The depth-averaged attenuation length of the ice column, 〈L〉 is shown to depend linearly on frequency. The best fit (95% confidence level) is 〈L(ν)〉= (460±20) − (180±40)ν m (20 dB km−1), for the frequencies ν = [0.100–0.850] GHz, assuming no reflection loss. The mean electric-field reflection coefficient is (1.7 dB reflection loss) across [0.100–0.850] GHz, and is used to correct the attenuation length. Finally, the reflected power rotated into the orthogonal antenna polarization is <5% below 0.400 GHz, compatible with air propagation. The results imply that Moore’s Bay serves as an appropriate medium for the ARIANNA high-energy neutrino detector.

In-Situ Measurements of the Activation Energy for D.C. Conduction in Polar ice

1979 ◽  
Vol 22 (87) ◽  
pp. 237-246
Author(s):  
Charles R. Bently
Keyword(s):  
Activation Energy ◽  
Impurity Content ◽  
Apparent Temperature ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
Metamorphic History ◽  
True Activation Energy ◽  
Resistivity Variation ◽  
Ionic Impurity

AbstractElectrical resistivity measurements were carried out at station J9 on the Ross Ice Shelf where temperature measurements were available to a depth exceeding three-quarters of the thickness of the shelf. As in a previously published study at a point about 30 km up-steam (Bentley, 1977), the apparent resistivities fit well to a model based upon a steady-state ice shelf with zero bottom balance-rate and an apparent activation energy in the solid ice of 0.15 to 0.25 eV (14–24. kJ mol−1), with preference for the lower end of the range. This model also fits the observed temperature data almost perfectly. Causes of resistivity variation with depth other than the temperature, such as impurity content, metamorphic history, grain size and crystal orientation, probably do not strongly affect the resistivity depth function. Our conclusion is that the true activation energy in the solid ice is less than 0.25 eV (24 kJ mol−1) and perhaps as small as 0.15 eV (14 kJ mol−1), although a reduction by a factor of two or three in the ionic impurity concentration between 50 and 250 m depth cannot be entirely ruled out as a cause of the low apparent temperature effect. A note added in proof indicates that Herron and Langway (in press) have, in fact, reported a decrease in Na+ concentration with increasing depth by a factor of two or three.

scholarly journals Measurements of Ice Shelf Water beneath the front of the Ross Ice Shelf using gliders

2017 ◽  
Vol 58 (74) ◽  
pp. 41-50 ◽  
Author(s):  
Monica J.S. Nelson ◽  
Bastien Y. Queste ◽  
Inga J. Smith ◽  
Gregory H. Leonard ◽  
Benjamin G.M. Webber ◽  
...  
Keyword(s):  
Freezing Point ◽  
Potential Temperature ◽  
Open Water ◽  
Shelf Water ◽  
Ice Shelf ◽  
Point Temperature ◽  
Ross Ice Shelf ◽  
Ice Shelf Water ◽  
Surface Freezing

ABSTRACTMeasurements made by an underwater glider deployed near the Ross Ice Shelf were used to identify the presence of Ice Shelf Water (ISW), which is defined as seawater with its potential temperature lower than its surface freezing point temperature. Properties logged by the glider included in situ temperature, electrical conductivity, pressure, GPS location at surfacings and time. For most of the first 30 recorded dives of its deployment, evidence suggests the glider was prevented from surfacing due to being under the ice shelf. For dives under the ice shelf, farthest from the ice shelf front, ISW layers of varying thicknesses and depth locations were observed; between 2 m thick (centred at 231 m depth) to >93 m thick (centred at >360 m). For dives under the ice shelf, close to the ice shelf front, either no ISW was observed or ISW layers were centred at shallower depths (116–127 m). Thicker ISW layers (e.g. up to 250 m thickness centred at 421 m) were observed for some glider dives in open water in front of the Ross Ice Shelf. No in situ supercooling (water colder than the pressure-dependent freezing point temperature) was observed.

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