激光掩星探测大气水汽混合比的数值模拟

Number Simulation for Laser Occultation Measurement of Atmospheric Vapor Mixing Ratio

在低轨道空间站和伴飞卫星上分别安置激光发射机和接收机,同时发射和接收935nm短波红外水汽探测激光束脉冲对和765nm(位于氧气的A吸收带)近红外激光束脉冲对。935nm波段激光脉冲的一个探测波长对水汽的吸收较强,另一个参考波长对水汽的吸收相对较弱;765nm波段激光脉冲的一个波长对氧气的吸收较强和另一个波长对氧气的吸收较弱。光连线全程的双波长差分光学厚度和连线切点处的差分消光系数之间存在Abel变换关系。基于Abel积分变换,利用理想气体状态定律和大气准静态方程,用大气模式作为初值条件,进行数值计算。765nm波长对用来反演大气的压强和温度,935nm波长对用来反演大气水汽的密度。获得的水汽廓线分布的仿真结果以及误差分布表明,激光掩星具有探测对流层上-平流层下这一高度(5~14km)的水汽含量的潜力。

A laser transmitter and receiver are respectively arranged on the low-orbit space station and its companion satellite.Both the 935-nm short-wave infrared band vapor detection laser beam pulse pair and 765-nm near-infrared band laser beam pulse pair(located in the oxygen absorption A-band)are transmitted and received simultaneously.One detection wavelength of the 935-nm band pulse pair strongly absorbs water vapor and other reference wavelength exhibites relatively weak absorption of water vapor;one wavelength of the 765-nm band is strongly absorbed by oxygen and other wavelength is weakly absorbed by oxygen.An Abel transformation relation exists between the two-wavelength differential optical depth of the entire optical connection and differential extinction coefficient at the tangent point of the connection.Based on Abel integral transformation,the numerical calculation is performed using the ideal gas law and the atmospheric quasi-static equation,taken the atmospheric model as the initial condition.The 765-nm wavelength pair is used to invert the atmospheric pressure and temperature,whereas935-nm wavelength pair is used to invert the atmospheric water vapor density.Simulation results and error distribution of the water vapor profile distribution are obtained.Results show that laser occultation has the potential to detect the level of water vapor in the troposphere-stratosphere(5--14 km).