研究了激光雷达远距离探测时信号光的空间相干特性和接收口径尺寸对外差探测的归一化载噪比RnCN和视场角Ωf的影响。采用激光雷达远距离探测模型，给出部分相干光探测时RnCN的一般表达式和相应的接收理论。进一步数值模拟分析显示：当高斯型本振光斑尺寸大于接收口径大小时，RnCN达到饱和状态；空间相干长度和口径半径的增加都能提高RnCN，但会导致Ωf的降低。在理论和数值模拟的基础上，提出RnCN和Ωf的乘积正比于λ2，且此关系不受回波信号相干特性的影响。最后给出Hufnagel-Valley 5/7湍流模型下探测高度和地面距离对RnCN的影响。

The effects of signal spatial coherent characteristics and receiving aperture size on normalized carrier-to-noise ratio (RnCN) and field of view for coherent detection (Ωf) are investigated. In the model of remote laser radar detection, the expressions of RnCN and the receiving theory are presented. Further numerical simulations show that when the Gaussian local oscillation beam size is larger than the receiving aperture size, RnCN will reach saturation, in addition, the spatial coherent length and aperture radius can both improve RnCN, but will reduce Ωf. Based on the theoretical analysis and numerical simulation, the relation is presented that the product of RnCN and field of view is proportional to λ2, which is unaffected by the coherent characteristics. At last, the dependence of RnCN on the detection height and ground range under the turbulence model of Hufnagel-Valley 5/7 is analyzed.