基于CALIPSO卫星数据的斜程能见度反演

Estimation of slant-range visibility based on CALIPSO aerosol products

基于CALIPSO(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation)卫星气溶胶产品,采用平面平行辐射传输模型SBDART(Santa Barbara DISORT Atmospheric Radiative Transfer)研究天津地区的斜程能见度。首先,使用CALIPSO卫星2015—2019年气溶胶产品对气溶胶消光系数廓线等垂直方向气溶胶光学特性进行统计分析。然后,针对具有“衰减型”气溶胶消光系数廓线的天气,采用SBDART模型求解大气辐射传输方程,得到天空背景辐射亮度,最后依据斜程能见度定义反演得到准确的斜程能见度。进一步,对使用Koschmieder定律和经验公式计算获得的斜程能见度准确性进行评估。结果表明,与经验公式法相比,在低能见度天气条件下,使用Koschmieder定律反演得到的斜程能见度更为准确,其平均误差小于15.0%,均方根相对偏差小于17.6%。此外,还对气溶胶消光系数廓线进行了拟合,并在斜程能见度反演中使用拟合的消光系数。结果表明,在低能见度天气条件下,拟合参数与近地面消光系数具有较好的相关性。而使用拟合的气溶胶消光系数获得的斜程能见度准确度也较高,其平均误差小于7%,表明在特定天气条件下,可以利用近地面消光系数来估计消光系数廓线,用于斜程能见度反演。

We exploit the SBDART method to investigate the slant-range visibility of the Tianjin area using the aerosol product of the CALIPSO satellite.First,the aerosol optical properties such as extinction coefficient are studied based on the aerosol data of the year 2015-2019.The aerosol data are classified into four types based on the aerosol extinction coefficient profiles.Second,for the atmosphere possessing the""exponential decay"aerosol extinction coefficient profile,we exploit the SBDART method to solve the radiative transfer equation.The sky background radiance is obtained as the solution of the equation.In the end,the slant-range visibility is derived with high accuracy according to the definition of visibility for the first time.Further,the Koschmieder law and the known analytical formula are used to derive the slant-range visibility.The accuracy of the obtained slant-range visibility is evaluated.In the evaluation,the slant-range visibility obtained by the SBDART method is regarded as the reference.The simulation results show that in the low-visibility atmosphere the Koschmieder law is shown to induce smaller errors of slant-range visibility than the analytical formula.Its average error is smaller than 15.0%and the mean square relative deviation is smaller than 17.6%.Additionally,we fit the"exponential decay"aerosol extinction coefficient profile with the exponential function and use the fit aerosol extinction coefficient in calculating the slant-range visibility.It is found that the fitting parameter is closely correlated with the aerosol extinction coefficient at the ground which is accessible with the common ground-based observations.It is also shown that the corresponding slant-range visibility has high accuracy.Its average error is smaller than 7%.Hence,it is possible to predict the aerosol extinction coefficient profile using the aerosol extinction coefficient at the ground.Consequently,the slantrange visibility can be estimated.It is especially important in case the aerosol extinction coefficient profile is not accessible due to the absence of efficient atmosphere observation equipment.