A bistatic, high‐frequency, under‐ice, acoustic scattering model. II: Applications

Abstract

A model that has been developed to calculate the scatter produced by a high‐frequency acoustic pulse that originates from a stationary and arbitrarily located source; is incident on and scattered from an under‐ice surface characteristic of pack ice regions of the interior Arctic; and is detected by a stationary and arbitrarily located receiver is used to calculate a variety of acoustic data. Scattering from small‐scale surface roughness produced by ice blocks as well as from large‐scale surface roughness produced by ice keels is calculated and discussed. The effects of physical parameters on the scatter of a high‐frequency plane wave from an ice block whose physical and geometric parameters are characteristic of those found in the Arctic are calculated and discussed briefly. The ice block scattering model is modified to calculate the near field target strength of a circular ice piston as a function of incidence angle. When measured and modeled facet target strength data are compared, it is shown that, near normal incidence, measured and modeled target strength levels agree reasonably well, but that the details of their dependence on incidence angle are different and that differences between the measured and modeled target strength data increase as frequency increases. Monostatic reverberation time series, facet target strength distributions, and correlation data are calculated and compared with measured data for three Arctic sites, and it is shown that measured and modeled data agree reasonably well. For the Chukchi Sea site, a variety of monostatic and bistatic time series, distribution, and correlation data are calculated and discussed for ice keels and flat ice features as well as for the entire under‐ice surface. It is shown that the predominant large‐scale, under‐ice scatterers are ice keels; that ice keels increase reverberation levels; that the facets of ice blocks from which ice keels are composed produce high‐level echos or glints; that generally the spatial location of these high‐level echoes depends on source–receiver location, although some may persist from one location to the next; and that high‐level echos from ice facets are one of the principal means by which ice keels increase high‐frequency, under‐ice reverberation.