通信系统的信噪比与信道状态和收发电路噪声有关。通过对大气湍流指数与光强方差的分析，基于光强度调制建立了湍流大气Rytov指数与无线光通信系统接收信噪比之间的关系。分析了由光强闪烁引入乘性噪声的情况下，无线光通信系统接收信噪比与接收光强方差之间的关系；讨论了大气湍流乘性噪声常用的两种概率密度函数及其对接收光强信号的影响，得到了Rytov指数与光强方差、系统接收信噪比之间的关系。最后采用不同天气条件下测得的实验数据验证了结果。研究表明：在弱湍流环境下，光强方差与Rytov指数满足线性关系，相应的接收信噪比随着Rytov指数的增大而降低；在中强湍流环境下，光强方差趋近饱和，系统信噪比趋近于稳定值。

The signal-to-noise ratio (SNR) of communication system is variable with channel status and circuits noise. We analyze the turbulence index and irradiance variance, and then establish the relationship between Rytov index of the atmospheric turbulence and SNR of intensity modulation free space optical communication (FSO) system. Firstly, the multiplicative noise induced by irradiance is analyzed. The relationship between irradiance variance and SNR of the FSO system is introduced. Then two common noise models are introduced to simulate the multiplicative noise. The relationship among Rytov index, irradiance variance and SNR of FSO system is derived. At last, the experimental measurement data under different weather conditions are used to prove the simulation results. The results show that there is a linear relationship between Rytov index and variance of intensity in weak turbulent weather. SNR of FSO system relatively decreases as the Rytov index increases. While in medium to strong turbulent weather, variance of intensity converges towards saturation, and SNR tends to a stable value.