Olson Derek R, Lyons Anthony P
Oceanography Department, Naval Postgraduate School, Monterey, California 93943, USA.
University of New Hampshire, Durham, New Hampshire 03824, USA.
J Acoust Soc Am. 2021 Jan;149(1):28. doi: 10.1121/10.0002974.
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, σ, 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 σ 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 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.
当代高分辨率声纳系统使用宽带脉冲和长阵列来实现高分辨率。了解高分辨率声纳系统可能对海底散射场的定量测量产生的影响非常重要。定义了一个称为宽带散射截面的量，适用于高分辨率测量。针对具有幂律谱和后向散射几何形状的一维粗糙表面，研究了宽带散射截面σ和闪烁指数SI对分辨率的依赖性。使用积分方程和傅里叶合成，未发现σ与分辨率有关。非相干平均频域散射截面的带宽依赖性可忽略不计。SI随着分辨率的增加、掠射角的减小和谱强度的增加而增加。对于100和10 kHz的中心频率以及1.5、2和2.5的幂律谱指数，这一趋势得到了证实。使用一个关于斜率影响的代表性模型（受复合粗糙度近似启发），研究了声学分辨率尺度上的局部倾斜是强度波动原因的假设。结果发现，斜率部分地导致了波动，但其他效应，如多次散射和阴影也可能起作用。
