The retrieval of ice cloud microphysical and optical properties from satellite-based infrared observation remains a challenging research topic, partly because of the sensitivity of observed infrared radiances to many surface and atmospheric parametersthat vary on fine spatial and temporal scales. In this study, the sensitivity of an infrared-based ice cloud retrieval to effective cloud temperature is investigated, with a focus on the effects of cloud-top height and geometric thickness. To illustratethe sensitivity, the authors first simulate brightness temperatures at 8.5 and 11.0 mum using the discrete ordinates radiative transfer (DISORT) model for five cloud-top heights ranging from 8 to 16 km and for varying cloud geometric thicknesses of 1,2,3, and 5 km. The simulations are performed across a range of visible optical thicknesses from 0.1 to 10 and ice cloud effective diameters from 30 to 100 mum. Furthermore, the effective particle size and optical thickness of ice clouds are retrieved fromthe Moderate Resolution Imaging Spectroradiometer (MODIS) measurements on the basis of a lookup-table approach. Specifically, the infrared brightness temperatures are simulated from the collocated Atmospheric Infrared Sounder (AIRS) level-2 product at 28atmospheric levels and prescribed ice cloud parameters. Variations of the retrieved effective particle size and optical thickness versus cloud-top height and geometric thickness are investigated. Results show that retrievals based on the 8,5- and 11.0-mum bispectral approach are most valid for cloud-top temperatures of less than 224 K with visible optical thickness values between 2 and 5. The present retrievals are also compared with the collection-5 MODIS level-2 ice cloud product.
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机译：从基于卫星的红外观测中检索冰云的微物理和光学特性仍然是一个具有挑战性的研究课题，部分原因是观测到的红外辐射对许多在精细的时空尺度上变化的表面和大气参数的敏感性。在这项研究中，研究了基于红外的冰云检索对有效云温度的敏感性，重点是云顶高度和几何厚度的影响。为了说明灵敏度，作者首先使用离散坐标辐射转移（DISORT）模型在8至16 km的五个云顶高度以及1,2,3的不同云几何厚度下模拟了8.5和11.0 mum处的亮度温度，和5公里。在范围从0.1到10的可见光学厚度和从30到100微米的冰云有效直径范围内执行模拟。此外，基于查找表方法，从中分辨率成像光谱仪（MODIS）测量中检索出冰云的有效粒径和光学厚度。具体来说，红外亮度温度是通过并置的大气红外测深仪（AIRS）2级产品在28个大气层和规定的冰云参数进行模拟的。研究了检索到的有效粒径和光学厚度相对于云顶高度和几何厚度的变化。结果表明，基于8,5-和11.0-um双光谱方法的反演对于小于224 K的云顶温度，可见光学厚度值介于2和5之间的反演最为有效。 5 MODIS 2级冰云产品。
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