中文摘要：

基于时空滤波理论,采用相干函数、功率响应函数、扩展分布函数、双频函数四个系统函数较波导不变量更全面地描述了低频声场的相干结构.理论分析、仿真研究和海试数据处理都验证了低频声场存在稳定的干涉结构,当目标由远及近、又由近及远做匀速直线运动时,相干函数（LOFAR图）的干涉结构为一簇类双曲线;功率响应函数的干涉图表征了简正波群时延的差分,体现了其频散特性;扩展分布函数能反映LOFAR图上干涉条纹的斜率大小;而双频函数能体现相慢度的差分.各个系统函数均能特别突出干涉结构的某方面的特征,各有特色.

英文摘要：

Compared with the waveguide invariant, the interference structures in low-frequency acoustic field are more comprehensively described by four system functions： coherent function, power response function, spread function and dual-frequency function, from space-time filter theory. A stable interference structure in the low-frequency acoustic field is testified based on theoretical analysis, simulation and sea trial data processing. When the target moves in a uniform rectilinear motion from far to near then from near to far, the interference structure of coherent function （LOFARgram） appears to be a family of quasi hyperbolas; the interference structure obtained by power response function represents the group delay difference and the dispersive characteristic of the normal mode; and the phase slowness difference can be exhibited by dual-frequency function. Each system function owns special characteristics, which can give prominence to certain features of the interference structure.