Radiative Transfer Applications to the Remote Sensing of Ice Clouds: Theory and Experiment

该项目是首席研究员正在进行的冰云中辐射传输研究的延续，具体应用于卷云大气和实验室云室的遥感。首席研究员和他的研究生已经开发出一种方法，可以从可见光和近红外波长的航空和卫星偏振和反射率观测中推断冰晶的大小和形状。他们还采用了一种新的理论方法，利用1.38微米波段的反射谱来确定卷云中冰晶尺寸的垂直剖面。实验室活动包括建造一个云室，用来产生各种形状和大小的冰晶，并配备一个特殊的辐射感应平台。该观测装置利用成像光栅光谱仪同时测量可见光和近红外中若干散射角和特定波长的反射光和偏振，再现了卫星和飞机观测到的双向反射几何形状。利用傅里叶变换红外光谱仪测量了1.38微米区域的反射光谱，用于垂直剖面分析。该研究的更广泛影响包括推进对冰云中包含复杂形状、大小和方向的非球形晶体的辐射传输的理解。理论与实验相结合的方法为开发利用卫星、星载雷达和激光雷达推断卷云组成的新遥感方法提供了物理基础和验证数据，以支持天气和气候研究。它还为在气候模式中参数化冰云提供了正确的光散射和辐射特性，这些信息对于理解广泛分布的卷云对阳光反射的影响以及与温室变暖和气候反馈过程相关的热红外辐射的捕获至关重要。

This project is a continuation of the Principal Investigator's ongoing research on radiative transfer in ice clouds, with specific applications to remote sensing in both cirrus cloudy atmospheres and a laboratory cloud chamber. The Principal Investigator and his graduate students have developed a method to infer ice crystal size and shape from airborne and satellite polarization and reflectance observations at visible and near-infrared wavelengths. They also employ a new theoretical approach using the reflected line spectrum in the 1.38 micrometer band to determine the vertical profile of ice crystal size in cirrus clouds. Laboratory activities include construction of a cloud chamber used to generate ice crystals of various shapes and sizes and equipped with a special radiation sensing platform. The observational apparatus measures the reflected light and polarization simultaneously at several scattering angles and at specific wavelengths in the visible and near-infrared by using imaging grating spectrometers, in a way that reproduces the bidirectional reflection geometry observed by satellite and aircraft. The reflected spectrum in the 1.38 micrometer region is measured by a Fourier Transform Infrared Spectrometer for application to vertical profiling. The broader impacts of the research include advancing the understanding of radiative transfer in ice clouds containing nonspherical crystals of intricate shape, size, and orientation. The combined theoretical and experimental approach provides the physical foundation and validation data for the development of new methods of remote sensing to infer cirrus cloud composition from satellites and space-borne radar and lidar in support of weather and climate research. It also supplies the correct light scattering and radiative properties of ice clouds for their parameterization in climate models, which information is critical for understanding the effect of widespread cirrus clouds on the reflection of sunlight and the trapping of thermal infrared radiation associated with greenhouse warming and climate feedback processes.