A comparative experiment on under-ice acoustic scattering in the marginal ice zone

For several years a series of ambient noise experiments has been conducted in the marginal ice zone (MIZ) off the east coast of Greenland from a fixed-wing airborne platform. In the spring of 1991, in addition to ambient noise measurements, a propagation experiment will also be attempted, aimed at establishing the effect of scattering due to the under surface of the ice cover. Parallel to the ice edge, two lines of omnidirectional sonobuoys will be deployed over a distance of about 100 km, one line about 1 km out in the open ocean and the other 1 km within the ice field. Explosive shots will be detonated at both ends of the dual line. Being so close, the primary difference between the propagation conditions down the two lines is in the scattering from the ice cover relative to that from the open-sea surface—bathymetry and sound-speed profiles being essentially the same. To support this experiment AXBTs will be deployed along both lines of buoys, although, in view of salinity variations in the vicinity of the ice, airborne expendable sound velocimeters would be preferable. These are planned for future Arctic experiments. An airborne technique for measuring the under-ice profile would also be highly desirable.