A New Approach to Electromagnetic Scattering from Ice Crystal Aggregates for Improving Quantitative Radar Measurements of Clouds and Precipitation

这项研究的目的是提高定性和定量的解释雷达测量的云和降水组成的冰晶和它们的聚集。 聚集体是地球仪降水面积分数的主要冰相贡献者。 美国和世界各地的卫星雷达系统和越来越多的地面研究雷达以毫米波频率工作，并专注于云的定性和定量表征。最近的研究表明，误差超过一个数量级的毫米波雷达截面的聚合物。 一种新的聚集体建模方法提供了一种有效和准确地确定不规则形状颗粒的雷达截面的途径。 提高冰粒雷达散射截面的计算精度是提高我们对层状云、融化层和冰降水毫米波雷达观测的理解的必要条件。这项研究将通过一种新的建模方法来研究冰晶聚集体的电磁散射特性。 计算机技术和计算算法的进步使得评估具有良好定义的形状和组成的原始晶体的毫米波散射成为可能。 不规则形状的水凝物，如冰晶聚集体（雪花）已被建模为均匀的颗粒与球形或类球形的形状，通过一个有效的介质近似的介电常数。最近的研究表明，在毫米波长下，冰晶聚集体的这种“散装”模型方法导致其雷达截面的显着低估。这项研究使用自然界中出现的原始晶体类型（例如，针状、柱状晶体、树突、子弹状突起）。构成聚集体的原始晶体是由微小的冰球构成的。一个已建立的计算算法被用来评估以这种方式构建的聚集体的电磁散射特性。智力价值：这项研究带来了一种新的和有效的方法来准确地表征冰水凝物的电磁散射，这将用于模拟毫米波雷达观测云和开发解释雷达测量的算法。这项研究的结果将应用于云和降水的地面和空间遥感，卫星通信链路设计和天气研究。一名研究生和一名博士后研究员将参加这些研究活动。他们将接受进行研究所需的理论和实验方法和技术方面的培训。生成的电磁散射数据将通过网络上的数据库提供给研究界。

The goal of this research is to improve the qualitative and quantitative interpretation of radar measurements of clouds and precipitation composed of ice crystals and their aggregates. Aggregates are the dominant ice phase contributors to the area fraction of precipitation across the globe. Satellite radar systems and a growing number of ground-based research radars in the U.S. and around the world operate at millimeter wave frequencies and are focused on the qualitative and quantitative characterization of clouds. Recent studies have suggested errors in excess of an order of magnitude in the millimeter-wave radar cross sections of aggregates. A new approach to modeling aggregates provides a pathway to efficiently and accurately determine radar cross sections from irregular shaped particles. An improved accuracy of radar cross section calculations of ice particles is necessary to enhance our understanding of millimeter wave radar observations of stratiform clouds, melting layer, and ice precipitation. This research will be accomplished through a new modeling approach for studying the electromagnetic scattering characteristics of ice crystal aggregates. Advances in computer technology and computational algorithms have made it possible to evaluate millimeter wave scattering from pristine crystals with well defined shapes and composition. Irregularly shaped hydrometeors such as ice crystal aggregates (snowflakes) have been modeled as homogeneous particles with spherical or spheroidal shapes through an effective medium approximation of their dielectric constants. It has recently been shown that at millimeter wavelengths this "bulk" model approach for ice crystal aggregates leads to significant underestimation of their radar cross sections. This study models the complex shape and composition of aggregates using pristine crystal types that appear in nature (e.g., needles, columnar crystals, dendrites, bullet rosettes). The pristine crystals that makeup the aggregates are constructed using tiny ice spheres. An established computational algorithm is used to evaluate the electromagnetic scattering characteristics of the aggregates constructed in this manner.Intellectual merit: This research brings a new and efficient approach to accurately characterizing electromagnetic scattering from ice hydrometeors, which will be used for simulating millimeter wave radar observations of clouds and developing algorithms for the interpretation radar measurements.Broader impacts: Results from this study will find application in surface and space-based remote sensing of clouds and precipitation, satellite communication link design, and weather research. A graduate student and a postdoctoral fellow will participate in these research activities. They will be trained in both theoretical and experimental methodologies and techniques necessary for conducting the research. The generated electromagnetic scattering data will be made available to the research community through a database maintained on the web.