Near-Normal Incidence Scattering from Rough, Finite Surfaces: Kirchhoff Theory and Data Comparison for Arctic Sea Ice
Abstract
We apply Kirchhoff theory for the target strength of a rough, circular surface whose roughness is characterized by a two-dimensional, isotropic power-law wavenumber spectrum W2(K) = n2K-p2. Three nondimensional parameters are found that govern the target strength: Koa, n=n2ap2-4, , and PI =P2-1, where KO is the acoustic wavenumber, a is the radius of the surface, and p 1 is the spectral exponent of the one-dimensional power-law wavenumber spectrum. First, we discuss the general influence of p 1, and n on the target strength. Following that are calculations of average target strength of the ice/water interface of a submerged cylindrical block of ice, which are compared with individual realizations of measured target strengths of ice blocks for frequencies between 20 kHz and 80 kHz. Data and theory show that the (smooth surface) form function for a finite surface does not describe the observed diffraction pattern. Instead, the lobes of the pattern diminish and the nulls fill in - i.e., the total backscatter becomes more incoherent - as frequency increases or as the large wavenumber components of the roughness spectrum contribute more to the total acoustic return. These comparisons also allowed us to infer the rough surface statistics of the ice surface and the compressional sound speed structure within the skeletal zone of the ice.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 10, 1992
- Accession Number
- ADA254525
Entities
People
- Kevin L. Williams
- P. D. Mourad
Organizations
- University of Washington