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

冰晶聚集体电磁散射的新方法可改善云和降水的定量雷达测量

• 批准号: 1228180
• 负责人: Kultegin Aydin
• 金额: $ 49.62万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-11-01 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1228180&HistoricalAwards=false
• 关键词: New; Approach; Electromagnetic; Scattering; Ice

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.

这项研究的目标是提高对由冰晶及其聚集体组成的云和降水的雷达测量的定性和定量解释。 聚集体是全球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运行，专注于云的定性和定量表征。最近的研究表明，毫米波雷达聚合截面的误差超过一个数量级。 一种新的聚集体建模方法提供了一种有效、准确地确定不规则形状颗粒的雷达横截面的途径。 提高冰粒子雷达截面计算的准确性对于增强我们对毫米波雷达观测层状云、融化层和冰降水的理解是必要的。这项研究将通过一种新的建模方法来完成，用于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明确形状和成分的原始晶体的毫米波散射成为可能。 不规则形状的水凝物，例如冰晶聚集体（雪花），已通过其介电常数的有效介质近似被建模为具有球形或椭球体形状的均匀颗粒。最近的研究表明，在毫米波长下，这种冰晶聚集体的“整体”模型方法会导致其雷达截面的严重低估。这项研究使用自然界中出现的原始晶体类型（例如针状晶体、柱状晶体、树突、子弹花结）来模拟聚集体的复杂形状和成分。构成聚集体的原始晶体是使用微小的冰球构建的。已建立的计算算法用于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有效方法来准确表征冰水凝物的电磁散射，该方法将用于模拟毫米波雷达对云的观测并开发解释雷达测量的算法。更广泛的影响：由此产生的结果 研究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维护的数据库提供给研究界。