Resolution dependence of rough surface scattering using a power law roughness spectrum

TL;DR

This study investigates how high-resolution sonar measurements of rough seafloor surfaces depend on resolution, finding that the broadband scattering cross section is resolution-independent while scintillation index varies with resolution, angle, and spectral properties.

Contribution

It introduces the broadband scattering cross section for high-resolution sonar and analyzes its resolution dependence, revealing that it remains unaffected by resolution while fluctuations increase.

Findings

Broadband scattering cross section shows negligible bandwidth dependence.

Scintillation index increases with resolution, decreasing grazing angle, and higher spectral strength.

Slopes contribute to intensity fluctuations, but other effects like multiple scattering also play a role.

Abstract

Contemporary high-resolution sonar systems use broadband pulses and long arrays to achieve high resolution. It is important to understand effects that high-resolution sonar systems might have on quantitative measures of the scattered field due to the seafloor. A quantity called the broadband scattering cross section is defined, appropriate for high-resolution measurements. The dependence of the broadband scattering cross section, $\sigma_{bb}$ and the scintillation index, $SI$ on resolution was investigated for one-dimensional rough surfaces with power-law spectra and backscattering geometries. Using integral equations and Fourier synthesis, no resolution dependence of $\sigma_{bb}$ was found. The incoherently-averaged frequency-domain scattering cross section has negligible bandwidth dependence. $SI$ increases as resolution increases, grazing angle decreases, and spectral strength increases. This trend is confirmed for center frequencies of 100 kHz and 10 kHz, as well as for power-law spectral exponents of 1.5, 2, and 2.5. The hypothesis that local tilting at the scale of the acoustic resolution is responsible for intensity fluctuations was examined using a representative model for the effect of slopes (inspired by the composite roughness approximation). It was found that slopes are responsible in part for the fluctuations, but other effects, such as multiple scattering and shadowing may also play a role.