Monostatic seismoacoustic scattering from 45° oblique cylindrical hole in thick floating ice plate

Abstract

Laboratory ultrasonic modeling results are presented characterizing monostatic scattering of broadband pulsed seismoacoustic waves (2<ka<8) from a 45° oblique cylindrical hole in a thick floating ice plate. A vertical compressional disk transducer placed on the free surface of a floating plate is used to generate and detect diagonally propagating shear waves created by the vertical displacement of the disk [G. F. Miller and H. Pursey, Proc. R. Soc. London Ser. A 233, 55–69 (1955)]. Compressional, shear, and Rayleigh wave velocities are simultaneously obtained from the oblique hole reflections. Backscattering results from oblique empty and water filled holes in Plexiglas and ice models are compared. Data from a layered plate model shows the effect of velocity variation with depth on ray bending and monostatic scattering. In other experiments, the compressional transducer is located in the water below the floating plate. The described oblique hole monostatic reflection seismology method may be used to determine sea ice shear velocity using a compressional transducer on the free surface of the ice and a 45° hole made by a coring machine such as the PICO 45° ice coring rig currently used in sea ice electromagnetic and optical oceanography. One-sided accurate velocity measurements may be achieved because the wave propagation distance between transducer and reflection point deep inside the ice can be determined from the surface. The findings are applicable to NDE and geophysics. [Work supported by ONR.]