Thickness and Structure of Antarctic Sea Ice Measured by Drilling and Impulse Radar

Abstract

Sea ice thickness was profiled in investigating the internal structure of sea ice in August 1982 near Syowa Station, East Antarctica, by drilling and using an impulse radar system. In this connection, the anisotropic properties of sea ice were studied by rotating the radar antenna on the horizontal surface of ice around the vertical axis.Ice cores 155 cm long were drilled for analysis of their internal structure, which showed that a brine-soaked layer existed at the depth of 90 cm. This layer corresponded to an internal echo of very strong intensity at this depth that did not change during the rotation of the antenna. Meanwhile, a bottom echo gave maxima and minima approximately every 90 degrees of rotation of the antenna; this alternation is attributable to the structure of newly grown ice with the preferred c-axis orientation. From these findings we consider that two types of sea ice covered the area near Syowa Station: one with a brine-soaked layer; the other without. Irregularities in shape of the bottom echo suggest that the sea ice plane was composed of accumulated small plates of sea ice. INTRODUCTIONPhysical and electromagnetic properties of sea ice were characterized by data analyzed from cores drilled at several points on the surface of a firn layer on an ice shelf Morey 1979, Kovacs andGow 1975). The thickness of the sea ice was profiled by direct measurements of the drilled cores, and also by a remote sensing technique using an impulse radar system which conducted continuous sounding onto this surface from which profiling was possible.Electromagnetic properties of sea ice, which vary considerably, are reflected on radar echoes during soundings. This makes it possible to divide sea ice into several types as well as disclosing its anisotropic structure. Interpretation of internal and bottom echoes was supported by our analysis of the drilled sea ice cores.