Surface and basal boundary conditions at the Southern McMurdo and Ross Ice Shelves, Antarctica (original) (raw)

2019, Journal of Glaciology

ABSTRACTWe derive the surface and basal radar reflectance and backscatter coefficients of the southern McMurdo Ice Shelf (SMIS) and part of the nearby Ross Ice Shelf (RIS), Antarctica, from radar statistical reconnaissance using a 60-MHZ airborne survey. The surface coefficients are further inverted in terms of snow density and roughness, providing a spatial distribution of the processes contributing to the surface boundary conditions. We disentangle the basal coefficients from surface transmission losses, and we provide the basal coherent content, an indicator of the boundary geometric disorder that is also self-corrected from englacial attenuation. The basal radar properties exhibit sharp gradients along specific iso-depths, suggesting an abrupt modification of the ice composition and geometric structure. We interpret this behavior as locations where the pressure-melting point is reached, outlining fields of freezing and melting ice. Basal steps are observed at both SMIS and RIS, ...

High-resolution radar mapping of internal layers of a subpolar ice cap, King George Island, Antarctica

2004

A GPR survey was carried out to investigate the structure and hydrology of King George Island subpolar ice cap, Antarctica. This study was part of a larger investigation on the mass balance of Lange Glacier (62 ◦ 07’S, 58 ◦ 36’W), an outlet ice mass that is receding. The strongest signal in all reflection profiles is due to the presence of free water. Sections show strong near-surface reflectors sitting on weaker ones above the water table. Below the water table, reflectors become strong again, displaying many discrete events that reach the end of the sections. Varying antenna configuration causes an important distinction in radar response for the same subsurface. A nearby snow and ice core was used to calibrate the top section of the GPR images.

Radar signatures beneath a surface topographic lineation near the outlet of Kamb Ice Stream and Engelhardt Ice Ridge, West Antarctica

Annals of Glaciology, 2009

Visible and infrared satellite images reveal numerous lineations on the Siple Coast region of West Antarctica. We used 5 MHz ice-penetrating radar to probe the interior and the bed of the ice sheet beneath a lineation at the boundary between Engelhardt Ice Ridge and flat-ice terrain to the south of the Kamb Ice Stream (KIS) outlet. Results show curved reflectors that emerge from the bed beneath 600 m thick ice. The tops of the reflectors extend about 100m into the ice above the bed, where they become almost horizontal. Apparent reflectivity of the horizontal section is about 20 dB less than that of the bed. We conclude that the likely cause of such strong reflection is sea water that was accreted into basal crevasses when the flat-ice terrain was floating. Internal layers are warped downward just downslope from the basal reflectors. It is thought that the downwarping was caused by localized basal melting in the past. The spatial pattern of downwarping suggests that localized basal m...

Radar characterization of the basal interface across the grounding zone of an ice-rise promontory in East Antarctica

Annals of Glaciology, 2012

Radar power returned from the basal interface along a 42 km long profile over an ice-rise promontory and the adjacent Roi Baudouin ice shelf, Dronning Maud Land, East Antarctica, is analyzed to infer spatial variations in basal reflectivity and hence the basal environment. Extracting basal reflectivity from basal returned power requires an englacial attenuation model. We estimate attenuation in two ways: (1) using a temperature-dependent model with input from thermomechanical ice-flow models; and (2) using a radar method that linearly approximates the geometrically corrected returned power with ice thickness. The two methods give different results. We argue that attenuation calculated using a modeled temperature profile is more robust than the widely used radar method, especially in locations where depth-averaged attenuation varies spatially or where the patterns of basal reflectivity correlate with the patterns of the ice thickness.

A comparison of basal reflectivity and ice velocity in East Antarctica

The Cryosphere, 2010

Ground-based radio echo sounding data acquired along the 1700 km US-ITASE traverse have been used to determine ice attenuation and relative basal reflectivity across the major catchments funneling ice from East Antarctica to the Ross Ice Shelf. We find that basal reflectivity varies locally by up to 40 dB which we interpret as due to changes in the phase state

Synthetic aperture radar detection of the snowline on Commonwealth and Howard Glaciers,Taylor Valley, Antarctica

Annals of Glaciology, 2002

Synthetic aperture radar (SAR) images of Taylor Valley, Antarctica, were acquired in January 1999 in coordination with ground-based measurements to assess SAR detection of the snowline on dry polar glaciers. We expected significant penetration of the radar wave resulting in an offset of the SAR-detected snowline relative to the true snowline. Results indicated no detectable displacement of the SAR snowline. Snow depths of 15 cm over ice can be detected on the imagery. We hypothesize that the optical depth of thin snowpacks is enhanced by reflection and refraction of the radar beam by internal snow layers. The enhanced optical depth increases the volume scattering, and thereby enhances backscatter sufficiently to be detected by the SAR. Consequently, SAR imagery may be used directly to image the position of transient snowlines in dry polar regions.

Loading...

Loading Preview

Sorry, preview is currently unavailable. You can download the paper by clicking the button above.