Mode-concept for individualising the Z-R-relation for precipitation radar

用于个性化降水雷达 Z-R 关系的模式概念

• 批准号: 5448298
• 负责人: Dr. Gerhard Peters, since 11/2005
• 金额: --
• 依托单位: Meteorologisches Institut (MI)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2005
• 资助国家: 德国
• 起止时间: 2004-12-31 至 2010-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/5448298?language=en
• 关键词: Mode; concept; individualising; relation; precipitation

The remote sensing technique for precipitation by means of radar generally allows for the online determination of areal precipitation, as needed for example as input data for runoff and flood forecast simulations. Traditionally the calculation of precipitation rates from radar reflectivities applies a power law conversion function which is either derived empirically as a climatological mean or theoreticall based on the ideal equilibrium case. A comparison of derived rainrates with measured ones shows errors up to a factor of 5 at radar pixel level when a static power law Z-R relation is applied. Many previous attempts to characterise drop size distributions in terms of precipitation or weather types have not been successful mainly because it was assumed that only large scale meteorological structures are of importance for discrimination. In the mode concept to be developed in this proposal the Z-R relation shall be determined by superimposing several drop modes, thus allowing to take also small scale meteorological phenomena into account. The relative contributions of the different drop modes will be determined systematically from available long-term observations of drop size distributions and ancillary meteorological criteria like precipitation intensity, vertical extension of the cloud, stratiform or convective type of precipitation, height of the zero degree layer, type of vertical reflectivity profile, and others. Primarily the average relative contributions of up to four discrete dropmodes shall be determined for typical precipitation types and processes. With the possibility to identify these precipitation processes and types in the radar image or data sets the precipitation rate can be later derived from look-up tables allowing for the derivation of optimal combinations of the drop modes. The validity of the empirically determined relations will be investigated and validated by the use of the comprehensive droplet spectra measured during the Special Observation Period (SOP) from ground based disdrometers and Micro Rain Radars of the partners witing AQUARadar.

利用雷达进行降水遥感技术通常可以在线确定区域降水，例如作为径流和洪水预报模拟的输入数据。传统上，根据雷达反射率计算降水率采用幂律转换函数，该函数要么根据经验作为气候平均值导出，要么根据理想平衡情况从理论上导出。将导出的降雨率与测量的降雨率进行比较，结果表明，当应用静态幂律 Z-R 关系时，雷达像素级的误差高达 5 倍。先前许多尝试根据降水或天气类型来表征液滴尺寸分布均未成功，主要是因为人们认为只有大尺度气象结构对于区分具有重要意义。在本提案中要开发的模式概念中，Z-R关系应通过叠加多个下降模式来确定，从而允许也考虑小尺度气象现象。不同雨滴模式的相对贡献将根据雨滴尺寸分布的长期观测和辅助气象标准（如降水强度、云的垂直延伸、降水的层状或对流类型、零度层的高度、垂直反射率剖面的类型等）系统地确定。首先，应确定典型降水类型和过程的最多四种离散下降模式的平均相对贡献。由于能够在雷达图像或数据集中识别这些降水过程和类型，随后可以从查找表中导出降水率，从而导出降水模式的最佳组合。将通过使用在特别观测期 (SOP) 期间从地面测速仪和 AQUARadar 合作伙伴的微雨雷达测量的综合液滴光谱来研究和验证凭经验确定的关系的有效性。