Torres Benjamin, Dubovik Oleg, Fuertes David, Schuster Gregory, Cachorro Victoria Eugenia, Lapyonok Tatsiana, Goloub Philippe, Blarel Luc, Barreto Africa, Mallet Marc, Toledano Carlos, Tanré Didier
Laboratoire d'Optique Amosphérique, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France.
GRASP-SAS, Remote sensing developments, Université des Sciences et Technologies de Lille, Villeneuve d'Ascq, France.
Atmos Meas Tech. 2017 Oct;10(10):3743-3781. doi: 10.5194/amt-10-3743-2017. Epub 2017 Oct 12.
This study evaluates the potential of using aerosol optical depth ( ) measurements to characterise the microphysical and optical properties of atmospheric aerosols. With this aim, we used the recently developed GRASP (Generalized Retrieval of Aerosol and Surface Properties) code for numerical testing of six different aerosol models with different aerosol loads. The direct numerical simulations (self-consistency tests) indicate that the GRASP-AOD retrieval provides modal aerosol optical depths (fine and coarse) to within 0.01 of the input values. The retrieval of the fine-mode radius, width and volume concentration are stable and precise if the real part of the refractive index is known. The coarse-mode properties are less accurate, but they are significantly improved when additional a priori information is available. The tests with random simulated errors show that the uncertainty in the bimodal log-normal size distribution parameters increases as the aerosol load decreases. Similarly, the reduction in the spectral range diminishes the stability of the retrieved parameters. In addition to these numerical studies, we used optical depth observations at eight AERONET locations to validate our results with the standard AERONET inversion products. We found that bimodal log-normal size distributions serve as useful input assumptions, especially when the measurements have inadequate spectral coverage and/or limited accuracy, such as moon photometry. Comparisons of the mode median radii between GRASP-AOD and AERONET indicate average differences of 0.013 μm for the fine mode and typical values of 0.2-0.3 μm for the coarse mode. The dominant mode (i.e. fine or coarse) indicates a 10 % difference in mode radii between the GRASP-AOD and AERONET inversions, and the average of the difference in volume concentration is around 17 % for both modes. The retrieved values of the fine-mode (500) using GRASP-AOD are generally between those values obtained by the standard AERONET inversion and the values obtained by the AERONET spectral deconvolution algorithm (SDA), with differences typically lower than 0.02 between GRASP-AOD and both algorithms. Finally, we present some examples of application of GRASP-AOD inversion using moon photometry and the airborne PLASMA sun photometer during the ChArMEx summer 2013 campaign in the western Mediterranean.
本研究评估了利用气溶胶光学厚度（ ）测量来表征大气气溶胶的微观物理和光学特性的潜力。为此，我们使用了最近开发的GRASP（气溶胶和表面特性广义反演）代码，对六种不同气溶胶负荷的不同气溶胶模型进行数值测试。直接数值模拟（自洽性测试）表明，GRASP-AOD反演提供的模态气溶胶光学厚度（细模态和粗模态）与输入值的误差在0.01以内。如果已知折射率的实部，细模态半径、宽度和体积浓度的反演是稳定且精确的。粗模态特性的准确性较低，但当有额外的先验信息时会有显著改善。随机模拟误差测试表明，双峰对数正态粒径分布参数的不确定性随着气溶胶负荷的降低而增加。同样，光谱范围的减小会降低反演参数的稳定性。除了这些数值研究，我们还利用了八个AERONET站点的光学厚度观测数据，将我们的结果与标准的AERONET反演产品进行验证。我们发现双峰对数正态粒径分布是有用的输入假设，特别是当测量的光谱覆盖不足和/或精度有限时，如月光度测量。GRASP-AOD和AERONET之间模态中值半径的比较表明，细模态的平均差异为0.013μm，粗模态的典型值为0.2 - 0.3μm。主导模态（即细模态或粗模态）表明GRASP-AOD和AERONET反演之间模态半径的差异为10%，两种模态体积浓度差异的平均值约为17%。使用GRASP-AOD反演得到的细模态 （500）值通常介于标准AERONET反演得到的值和AERONET光谱反卷积算法（SDA）得到的值之间，GRASP-AOD与这两种算法之间的差异通常低于0.02。最后，我们展示了在2013年夏季ChArMEx活动期间，在地中海西部利用月光度测量和机载PLASMA太阳光度计进行GRASP-AOD反演应用的一些示例。
