Unusual radar echoes from the greenland ice sheet.

Airborne radar images of part of the Greenland ice sheet reveal icy terrain whose radar properties are unique among radar-studied terrestrial surfaces but resemble those of Jupiter's icy Galilean satellites. The 5.6- and 24-centimeter-wavelength echoes from the Greenland percolation zone, like the 3.5- and 13-centimeter-wavelength echoes from the icy satellites, are extremely intense and have anomalous circular and linear polarization ratios. However, the detailed subsurface configurations of the Galilean satellite regoliths, where heterogeneities are the product of prolonged meteoroid bombardment, are unlikely to resemble that within the Greenland percolation zone, where heterogeneities are the product of seasonal melting and refreezing.

Effects of water and ice layers on the scattering properties of diffuse reflectors.

Measurements were made of the angular distribution of power scattered from a diffuse reflector illuminated by a laser beam directed normal to the surface of the reflector. Experiments were performed on dry, wet, and ice-covered planar targets. They revealed that the diffuse component of scattered power from a wet or icecovered target is reduced by an amount proportional to the inverse of the square of the index of refraction of the layer, which is consistent with simple theory. Backscattered radiation from a water-or ice-covered target was found to be enhanced compared with that from a dry target in the region about a cone centered on the line normal to the target. The half-angles of the cones for dry, water-covered, and ice-covered targets were 2.5, 12.5, and 30 degrees , respectively. The large half-angles of the covered targets may be due to multiple reflections within the layer. Small air bubbles in the ice and the roughness of the ice surface may be responsible for the particularly large increase in half-angle of the ice-covered target.

Rheology of glacier ice.

A new method for calculating the stress field in bounded ice shelves is used to compare strain rate and deviatoric stress on the Ross Ice Shelf, Antarctica. The analysis shows that strain rate (per second) increases as the third power of deviatoric stress (in newtons per square meter), with a constant of proportionality equal to 2.3 x 10(-25).