Radio scattering characteristics of Antarctic ice sheet using airborne radio echo sounding data

Some characteristics of radio wave scattering from ice sheet surfaces, inner volume and the bedrock surface are inferred from data obtained from 179 MHz airborne radio echo sounder data during the 27th Japanese Antarctic Research Expedition. A-scope data from sounder with wide antenna beams include information on the scattering characteristics at the ice sheet surface, within the ice sheet itself, and at the bedrock sub-surface. Characteristics are modeled from the A-scope form by using expanded radar equations which allow determination of the roughness of the ice sheet and bedrock surfaces. Results indicate a strong dependence of backscatter from the ice surface with incidence angle and a weak dependence in backscatter from the bedrock

SUBGLACIAL WATER LAYER AND GROUNDING LINE DERIVED FROM BACKSCATTERING COEFFICIENTS OF RADIO ECHO SOUNDING IN THE SHIRASE GLACIER AND ROI BAUDOUIN ICE SHELF, EAST ANTARCTICA

In the 1986-87 austral summer, ice thickness measurements using a new designed airborne radio echo sounding system were carried out in the Shirase Glacier drainage basin and Roi Baudouin lce Shelf, Princess Ragnhild Coast, East Antarctica. The accurate determination of ice thickness during the flight was supported by measurements of surface elevation calibrated over the open sea at the beginning and end of each flight with radar altimetry. Location was determined by an OMEGA system and satellite Global Positioning System (GPS). The ice sheet profile along the flow line of the Shirase Glacier and ice shelf along the flight line from Asuka Camp to the Roi Baudouin Ice Shelf were determined and bottom features such as subglacier water layer and grounding line were clarified by finding the radio backscattering coefficients. The accurate surface elevation and backscattering coefficients obtained from the radar equation are adequate for locating the grounding line and detecting its accurate location within a few kilometers. It is also shown that the subglacial water layer was inferred from the backscattering coefficients of radio echo sounding along the Shirase Glacier flow line. The water layer thickness is estimated to be 0-30cm at the interface between the base of the ice sheet and the bedrock in the regions downstream of Shirase Glacier

Step frequency radar for the measurement of sea ice thickness

The preliminary experiments have been carried out to test the fundamental functions of the step frequency radar. This radar aims at measuring the thickness of the Antarctic sea ice, which transmit 32 different frequencies in a stepwise fashion between 300 and 796MHz. The radar has the following details; a) the maximum transmitting power : 400mW, b) the range resolution : about 0.3m in the air, c) the maximum observable distance without an ambiguity; about 9.1m in the air, and d) the transmitting and receiving antennas : two cavitybacked spiral antennas whose sense of circular polarization is mutually opposite. The experiments in the anechoic chamber have proved that this radar system could have successfully detected the iron pipe buried in the dry sand and the aluminum plate placed under the sand box. This result suggests that with this radar system an airborne survey of the sea ice thickness will become possible

CHARACTERISTICS OF RADIO ATTENUATION COEFFICIENT ON THE SØR RONDARNE ICE SHEET, ANTARCTICA

The depth-averaged attenuation coefficients are calculated from the echo pattern measurements from internal ice. The attenuation coefficients around the Sør Rondane Mountains, Antarctica were mapped from the 179MHz airborne radio-echo sounder, which made observations during 1986. The map shows a tendency of decreasing attenuation as the surface altitude of the ice sheet increases. This result is interpreted by using the relationship between attenuation coefficients and ice temperature. In addition, a cosine relationship was found between attenuation coefficients and the angle of the radar polarization from the topographic contour. The dynamic range of the variety of the attenuation coefficients is 1.2dB/100m. If the ice flow is perpendicular to the topographic contour, the ice flow direction will be derived from the polarimetric radar observation

Step frequency radar experiments on the Antarctic sea ice

Step frequency radar experiments have been carried out on sea ice near Syowa Station as part of the 27th Japanese Antarctic Research Expedition to develop an airborne sensor for measuring vertical sea ice structures. Step frequency radar has characteristics of high resolution and low frequency (UHF band), which is an advantage in measuring sea ice. The experiments are the first application of this radar for measuring sea ice thickness. The radar transmits 32 different frequencies in a stepwise fashion between 300 and 796 MHz and measures the amplitude and phase of reflected waves at each frequency. The discrete Fourier transform of the 32 complex values of signals indicates the distance of vertical sea ice structures. The range resolution is about 15cm in sea ice. The experimental results showed that the radar system could successfully measure vertical sea ice structures : (1) The distance between the surface and the snow/ice interface or between the surface and the sea ice bottom deduced by this method coincided with direct measurements in sample holes. (2) Snow depth was measured very clearly by the radar system

Internal layering detected by a microwave ice-radar in the Arctic ice cap (scientific paper)

Radar observations were carried out on the Agassiz ice cap in Canadian arctic territory using a newly developed high resolution ice-radar. The radar employed a microwave frequency (L-band) in order to realize resolution of less than 1m. Actual range resolution of the radar is about 63cm in ice. The radar can observe the bedrock topography and internal echoes with high resolution. Signals from bedrock up to 500 meters in depth were detected. The attenuation coefficient in the L-band frequency was calculated to be 0.05dB/m. Internal ice layers were observed from about 50m to 200m in depth. Internal layers detected by the radar were compared to the electrical conductivity of an ice core measured by ECM at the summit of the ice cap with almost the same resolution. Each peak of the radar echo corresponded to an ECM peak, but the relationship between echo intensity and ECM intensity is not clear

VERTICAL PROFILES OF ICE SHEET MEASURED WITH A MOBILE RADIO ECHO SOUNDER IN EAST QUEEN MAUD LAND, ANTARCTICA

The vertical profiles of the ice sheet over a wide area around Dome Fuji Station and along a route of about 1000km from Dome Fuji Station (77°22′S, 39°36′E, 3807m a. s. l.) to S16 (69°01′S, 40°03′E, 591m a. s. l.) were surveyed by a 179-MHz radio echo sounder with a continuous recording system. The survey was part of the Dome Fuji Project which started in the 33rd Japanese Antarctic Research Expedition (November 1991-March 1993). Reflected radio echoes from internal layers shallower than 2000m were successfully detected. Echoes from the bedrock, which represent the basal topography, were also measured even at places where the ice sheet on it was thicker than 3500m. The vertical profiles of radio echoes along the route indicate the regional characteristics of the internal layers. In the Dome Fuji Station area, the internal layers were stratified horizontally, indicating that the horizontal flow of ice is very slow there. On the other hand, the internal layers indicated in the vertical cross section near the coast appeared rather complicated, probably because of the large and non-uniform ice flow