Ground-based imaging remote sensing of ice clouds: uncertainties caused by sensor, method and atmosphere
Ground-based imaging remote sensing of ice clouds: uncertainties caused by sensor, method and atmosphere
复制标题
DOI：
10.5194/amt-9-4615-2016
复制
发表时间：
2016-09
影响因子：
3.8
通讯作者：
T. Zinner;P. Hausmann;Florian Ewald;L. Bugliaro;C. Emde;B. Mayer
中科院分区：
文献类型：
--
作者：
T. Zinner;P. Hausmann;Florian Ewald;L. Bugliaro;C. Emde;B. Mayer
抽象的。在这项研究中，介绍了一种方法的反演光学厚度和有效粒子大小的冰云在很宽的光学厚度范围内从地面透射辐射测量。卷云光学厚度低，微物理特性复杂，给云遥感带来了挑战。在透射率中，光学深度和辐射亮度之间的关系是模糊的。为了解决这种模糊性的检索利用光谱斜率的辐射率在485和560 nm之间，除了通常采用的组合的可见光和短波红外波长。检索灵敏度进行了广泛的测试，使用合成的测试光谱，其中引入不确定性的检索的所有参数进行了系统的变化：冰晶习性和气溶胶特性，仪器噪声，校准的不确定性和插值所需的检索过程中的查找表。最重要的误差来源是由于习惯假设的不确定性：平均在所有的测试光谱，系统偏差的有效半径检索的几个微米可能会出现。任何单个检索的统计不确定性都很容易超过10微米。光学厚度偏差大多低于1，而统计不确定性在1至2.5的范围内。为了演示和比较卫星数据的检索适用于观测的慕尼黑高光谱成像仪specMACS（光谱仪的慕尼黑气溶胶和云扫描仪）在Schneefernerhaus天文台（2650米a.s.l.）在2012年9月和10月的ACRIDICON-Zugspitze战役期间。结果进行了比较，以中分辨率成像光谱仪和SEVIRI卫星为基础的卷云检索（ACRIDICON -气溶胶，云，降水和辐射的相互作用和对流云系统的动力学;中分辨率成像光谱仪; SEVIRI -旋转增强可见光和红外成像仪）。考虑到我们的地面方法和卫星检索的确定的不确定性，比较显示出良好的协议范围内的云的情况下，在直接周围的自然变化。
Abstract. In this study a method is introduced for the retrieval of optical thickness and effective particle size of ice clouds over a wide range of optical thickness from ground-based transmitted radiance measurements. Low optical thickness of cirrus clouds and their complex microphysics present a challenge for cloud remote sensing. In transmittance, the relationship between optical depth and radiance is ambiguous. To resolve this ambiguity the retrieval utilizes the spectral slope of radiance between 485 and 560 nm in addition to the commonly employed combination of a visible and a short-wave infrared wavelength. An extensive test of retrieval sensitivity was conducted using synthetic test spectra in which all parameters introducing uncertainty into the retrieval were varied systematically: ice crystal habit and aerosol properties, instrument noise, calibration uncertainty and the interpolation in the lookup table required by the retrieval process. The most important source of errors identified are uncertainties due to habit assumption: Averaged over all test spectra, systematic biases in the effective radius retrieval of several micrometre can arise. The statistical uncertainties of any individual retrieval can easily exceed 10 µm. Optical thickness biases are mostly below 1, while statistical uncertainties are in the range of 1 to 2.5. For demonstration and comparison to satellite data the retrieval is applied to observations by the Munich hyperspectral imager specMACS (spectrometer of the Munich Aerosol and Cloud Scanner) at the Schneefernerhaus observatory (2650 m a.s.l.) during the ACRIDICON-Zugspitze campaign in September and October 2012. Results are compared to MODIS and SEVIRI satellite-based cirrus retrievals (ACRIDICON – Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems; MODIS – Moderate Resolution Imaging Spectroradiometer; SEVIRI – Spinning Enhanced Visible and Infrared Imager). Considering the identified uncertainties for our ground-based approach and for the satellite retrievals, the comparison shows good agreement within the range of natural variability of the cloud situation in the direct surrounding.