Andrews Mark, Gong Zheng, Ratilal Purnima
Department of Electrical and Computer Engineering, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA.
J Acoust Soc Am. 2009 Sep;126(3):1057-68. doi: 10.1121/1.3177271.
The matched filter enables imaging with high spatial resolution and high signal-to-noise ratio by coherent correlation with the expected field from what is assumed to be a discrete scatterer. In many physical imaging systems, however, returns from a large number of randomized scatterers, ranging from thousands to millions of individuals, are received together and the coherent or expected field vanishes. Despite this, it is shown that cross-spectral coherence in the matched filtered variance retains a pulse compression property that enables high-resolution imaging of scatterer population density. Analytic expressions for the statistical moments of the broadband matched filtered scattered field are derived in terms of the medium's Green's function, object scatter function, and spatial distribution using a single-scatter approximation. The formulation can account for potential dispersion in the medium and target over the signal bandwidth, and can be used to compare the relative levels of the coherent and incoherent scattered intensities. The analytic model is applied to investigate population density imaging of fish distributions in the Gulf of Maine with an ultrasonic echosounder. The results are verified with numerical Monte-Carlo simulations that include multiple scattering, illustrating that the single-scatter approximation is valid even for relatively dense Atlantic herring (Clupea harengus) schools.
匹配滤波器通过与假定为离散散射体的预期场进行相干相关，实现高空间分辨率和高信噪比成像。然而，在许多物理成像系统中，来自大量随机散射体（从数千到数百万个个体）的回波会一起被接收，相干或预期场消失。尽管如此，研究表明，匹配滤波方差中的互谱相干保留了脉冲压缩特性，从而能够对散射体群体密度进行高分辨率成像。利用单散射近似，根据介质的格林函数、目标散射函数和空间分布，推导了宽带匹配滤波散射场统计矩的解析表达式。该公式可以考虑介质和目标在信号带宽上的潜在色散，并可用于比较相干和非相干散射强度的相对水平。应用该解析模型，利用超声回声测深仪研究缅因湾鱼类分布的群体密度成像。结果通过包含多次散射的数值蒙特卡罗模拟得到验证，表明即使对于相对密集的大西洋鲱鱼群，单散射近似也是有效的。
