Source bearing and range estimation using an ice-mounted tri-axial geophone

Abstract

This paper presents results from Arctic field trials to estimate the bearing, range, and depth of an acoustic source in the water column using seismic particle motion measured at a tri-axial geophone on the sea ice surface. Measurements were carried out on smooth, rough, and ridged annual ice, and on a multi-year ice floe. Impulsive acoustic sources were deployed in the water at a variety of bearings and ranges from 0.2-50 km. Source bearings are estimated by applying polarization filters to suppress shear waves with transverse particle motion and computing the incident power as a function of radial look angle; the inherent 180-degree ambiguity is resolved by requiring prograde particle motion in the vertical-radial plane. Results indicate good bearing estimation (<10-degree average errors) at all ranges with little dependence on ice type. Source range and depth is estimated from the time difference between the water-borne arrival and ice seismic waaves. Results are limited due to strong attenuation of the seismic waves, with good range/depth estimation to <1 km for smooth annual and multi-year ice and <0.5 km for rough ice.