以辐射传输方程为基础,借助小角度近似条件,利用多次散射递归的逐级逼近来描述水体散射过程,推导得出水下辐射照度以及衰减系数的计算关系.着重讨论了激光在海水中的衰减特性,结果表明随着光学厚度的增加,各次散射光先增大后减小,相对辐射照度基本呈指数衰减,衰减趋势随单次散射反照率或者不对称因子的增大有所减缓.与蒙特卡罗方法模拟的结果进行比较,小散射角条件下多次散射近似方法的计算准确度优于单次散射近似,可以作为分析水下激光传播特性的参考依据.

The light propagation in water becomes complicated due to the scattering of water. Limited by optical thickness and other factors,the single scattering approximation is insufficient. Based on the radiative transfer equation and small angle approximation,the multiple scattering solve is gradually recursive to describe the whole scattering process. The calculation relation between underwater irradiance and the attenuation coefficient is deduced and the laser attenuation characteristic in seawater is discussed. The results show that,with the increase of optical thickness,each order scattering is first enhanced and then decreased,the relative irradiance attenuates exponentially,and the attenuation trend is declined when the single scattering albedo or asymmetric factor rise. Verified through Monte Carlo simulation method,the multiple scattering approximation method has a better accuracy than the single scattering approximation on the condition of small scattering angle and can be used as the reference for analysis of the underwater laser propagation.