Frehlich R G, Kavaya M J
Appl Opt. 1991 Dec 20;30(36):5325-52. doi: 10.1364/AO.30.005325.
The signal-to-noise ratio (SNR) and heterodyne efficiency are investigated for coherent (heterodyne detection) laser radar under the Fresnel approximation and general conditions. This generality includes spatially random fields, refractive turbulence, monostatic and bistatic configurations, detector geometry, and targets. For the first time to our knowledge, the effects of atmospheric refractive turbulence are included by using the path-integral formulation. For general conditions the SNR can be expressed in terms of the direct detection power and a heterodyne efficiency that can be estimated from the laser radar signal. For weak refractive turbulence (small irradiance fluctuations at the target) and under the Markov approximation, it is shown that the assumption of statistically independent paths is valid, even for the monostatic configuration. In the limit of large path-integrated refractive turbulence the SNR can become twice the statistically independent-path result. The effects of the main components of a coherent laser radar are demonstrated by assuming untruncated Gaussians for the transmitter, receiver, and local oscillator. The physical mechanisms that reduce heterodyne efficiency are identified by performing the calculations in the receiver plane. The physical interpretations of these results are compared with those obtained from calculations performed in the target plane.
在菲涅耳近似和一般条件下，对相干（外差探测）激光雷达的信噪比（SNR）和外差效率进行了研究。这种一般性包括空间随机场、折射湍流、单基地和双基地配置、探测器几何形状以及目标。据我们所知，首次通过使用路径积分公式纳入了大气折射湍流的影响。对于一般条件，SNR可以用直接探测功率和一个可从激光雷达信号估算的外差效率来表示。对于弱折射湍流（目标处的小辐照度波动）且在马尔可夫近似下，结果表明即使对于单基地配置，统计独立路径的假设也是有效的。在大路径积分折射湍流的极限情况下，SNR可能变为统计独立路径结果的两倍。通过假设发射机、接收机和本地振荡器为未截断高斯分布，展示了相干激光雷达主要组件的影响。通过在接收机平面进行计算，确定了降低外差效率的物理机制。将这些结果的物理解释与在目标平面进行计算所得到的解释进行了比较。
