Inversion of pack ice elastic wave data to obtain ice physical properties

Abstract

Geophones mounted on floating ice sheets can potentially provide data for a robust method to monitor mechanical properties of the ice. The technique relies on the measurement and inversion of low‐frequency elastic waves propagating in the ice. To test this hypothesis, several geophone systems were deployed on the Arctic ice as part of the Office of Naval Research Sea Ice Mechanics Initiative (SIMI), including a winter‐over system of 20 triaxial geophones at the fall 1993 SIMI camp. An inversion technique is discussed here through references to the literature and by analysis of geophone data, specifically those data collected on “clean” first‐year ice off Resolute Bay, Canada, and on highly irregular multiyear ice found at the fall SIMI camp. For undeformed first‐year ice, the inversion technique gave an estimate of ice properties that agreed well with known values, although extensive work remains to determine the effects of anisotropy and inhomogeneity. The geophone data for the nonuniform ice at the SIMI camp were very complex and difficult to analyze. The inversion yielded only trends in what can, at best, be termed effective ice thickness and bending rigidity; it is uncertain how these relate to actual ice properties. The SIMI geophone system demonstrated the feasibility of performing autonomous measurements of the characteristics of propagating waves in the Arctic ice; with continued study, it seems evident that such systems can be used in clean first‐year ice to monitor ice properties. However, extensive research is required to make this technique useful in multiyear or complex first‐year ice.