Steven M. Hodge

Radar internal layers from the Greenland Summit

Ice penetrating radar measurements made over the summit region of Greenland show returns from internal layers which can be used to augment the interpretation of climate information from the two deep cores recently recovered from this area. These reflecting surfaces, believed to represent isochrones, give information about the stress regime near the summit, and may aid in a better calibration of the age depth scale between the two cores — particularly in the lowest 10% of ice thickness where there is currently disagreement. The approximate depth at which internal echoes become discontinuous corresponds with the observations of steep inclinations and overturned folds on the scale of centimeters in the core samples. However the deepest internal layers which can be distinguished in the profiles place constraints on the scale and location of high angle or overturned folds.

Use of a new high-speed digital data acquisition system in airborne ice-sounding

A high-speed digital data acquisition and signal averaging system for borehole, surface, and airborne radio-frequency geophysical measurements was designed and built by the US Geological Survey. The system permits signal averaging at rates high enough to achieve significant signal-to-noise- enhancement in profiling, even in airborne applications. The first field use of the system took place in Greenland in 1987 for recording data on a 150 by 150-km grid centered on the summit of the Greenland ice sheet. About 6000-line km were flown and recorded using the new system. The data can be used to site a proposed scientific corehole through the ice sheet. >