The Underside of Arctic Sea Ice Imaged by Sidescan Sonar

Abstract

Despite extensive submarine operations in the Arctic, little is yet known about the three-dimensional morphology of the ice underside. Several studies have been done using upward-looking sonar1–7, which yields a linear profile of ice draft from which the distributions of features such as pressure ridges and leads may be derived. Such a profile gives no information about the spatial morphology or appearance of the ice bottom surface. In contrast, the upper ice surface has been well documented from airborne and satellite-borne sensors such as synthetic aperture radar, passive microwave, infrared and visual imaging. Here I report the first extensive set of imagery of the underside of sea ice in the Arctic Ocean. Sidescan sonar images show a distinct difference between the appearance of first-year ice and of multi-year ice. First-year ice has a smooth bottom except for a network of cracks, while multi-year ice is covered with an array of blisters or bulges. The clear discrimination between ice types enables sidescan sonar to be used as a means of validating airborne passive microwave data.