Sabra Karim G
Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0405, USA.
J Acoust Soc Am. 2010 Jun;127(6):3577-89. doi: 10.1121/1.3397612.
It has been demonstrated theoretically and experimentally that an estimate of the Green's function between two receivers can be obtained by cross-correlating acoustic (or elastic) ambient noise recorded at these two receivers. Coherent wavefronts emerge from the noise cross-correlation time function due to the accumulated contributions over time from noise sources whose propagation path pass through both receivers. Previous theoretical studies of the performance of this passive imaging technique have assumed that no relative motion between noise sources and receivers occurs. In this article, the influence of noise sources motion (e.g., aircraft or ship) on this passive imaging technique was investigated theoretically in free space, using a stationary phase approximation, for stationary receivers. The theoretical results were extended to more complex environments, in the high-frequency regime, using first-order expansions of the Green's function. Although sources motion typically degrades the performance of wideband coherent processing schemes, such as time-delay beamforming, it was found that the Green's function estimated from ambient noise cross-correlations are not expected to be significantly affected by the Doppler effect, even for supersonic sources. Numerical Monte-Carlo simulations were conducted to confirm these theoretical predictions for both cases of subsonic and supersonic moving sources.
理论和实验均已证明，通过对在两个接收器处记录的声学（或弹性）环境噪声进行互相关，可以获得这两个接收器之间格林函数的估计值。由于传播路径穿过这两个接收器的噪声源随时间的累积贡献，相干波前会从噪声互相关时间函数中出现。此前对这种被动成像技术性能的理论研究假设噪声源与接收器之间不存在相对运动。在本文中，利用驻相近似，针对固定接收器，在自由空间中从理论上研究了噪声源运动（例如飞机或船舶）对这种被动成像技术的影响。在高频情况下，利用格林函数的一阶展开，将理论结果扩展到更复杂的环境。尽管源运动通常会降低宽带相干处理方案（如时延波束形成）的性能，但研究发现，即使对于超音速源，从环境噪声互相关估计得到的格林函数预计也不会受到多普勒效应的显著影响。进行了数值蒙特卡罗模拟，以证实亚音速和超音速移动源两种情况下的这些理论预测。
