Comparison of ultrasonic measurements of acoustic scattering from hard infinitely thick striated surfaces with Twersky theory

Abstract

Ultrasonic laboratory scale measurements of scattering from an infinitely thick, striated surface were conducted to test the accuracy of the Twersky theory predictions. These measurements represent the first phase of a measurement program that is intended to provide a baseline and stimulus for refined theories of underice reflectivity and scattering, and will, in its next phase, consider randomly distributed and oriented half‐cylinders on plates. Results of the initial phase reveal that measured reflection coefficients are in excellent agreement with theory at grazing angles between 10° and 50°, when ka < 1 and when ka> 1, where k is the wavenumber and a is the average half‐cylinder depth. At intermediate frequencies, measured losses were substantially greater than predictions due to resonance scattering associated with the physical/geometrical properties of the half‐cylinders. These results imply that both theoretical and laboratory scale modeling of scattering from sea ice at intermediate frequencies must consider both geometrical and physical properties of the proturbances. [Work supported by ONR.]