The dual-frequency precipitation radar for the GPM core satellite
The dual-frequency precipitation radar for the GPM core satellite
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GPM核心卫星双频降水雷达
DOI：
10.1109/igarss.2003.1294221
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
S. Satoh
中科院分区：
文献类型：
--
作者：
T. Iguchi;H. Hanado;N. Takahashi;S. Kobayashi;S. Satoh
本文概述了全球降水使命的“核心”航天器上的双频降水雷达（DPR）的发展。I.在全球降水使命（GPM）中，计划在“核心”航天器上飞行双频降水雷达（DPR）。“核心”航天器作为一个高质量的参考平台，用于训练和校准与其他“星座”卫星上的被动微波辐射计一起使用的降雨反演算法。双频雷达预计将提供降雨率的准确估计，以及结合Ku和Ka波段雷达回波的雨滴大小分布（DSD）参数。本文概述了DPR的发展现状。在此介绍之后，我们讨论了影响DPR设计的关键问题。二. DPR要求A. DPR与GPM的相关性DPR与GPM的相关性在于雷达能够测量风暴结构、降雨率、雨滴尺寸分布（DSD）、路径综合衰减以及被动传感器无法获得的其他有用参数。在最新的设计中，DPR由Ku波段和Ka波段信道组成。Ku波段雷达与TRMM降水雷达（PR）大致相同，但有一些改进。Ka波段雷达对小雨和小雪具有很高的灵敏度。来自两个通道的数据的组合将提供液滴尺寸分布参数的准确估计。Ka波段雷达将以两种不同的模式同时采集回波数据。一种是高灵敏度模式，用于小雨和雪的检测;另一种是匹配波束模式，其中Ka和Ku波段雷达通道的采样体积匹配，用于收集来自相同目标的双频回波。在后一模式中收集的数据用于DSD参数的估计。在匹配波束模式下，采用250米的距离分辨率，而在高灵敏度模式下，计划采用500米的距离分辨率。目前的雷达设计在两个雷达通道都采用有源相控阵天线，以充分利用TRMM的经验。DPR将提供具有高空间分辨率的水凝物分布的三维信息。这些资料对风暴结构的研究是很有价值的。DPR的准确降雨估计预计将用于校准核心卫星上辐射计的相应估计。然而，DPR的主要重要性在于它可以提供区域和季节风暴结构的统计数据以及DSD参数。由于被动微波辐射计的降水反演算法必须确定性地或统计性地假设风暴的垂直结构，因此可靠的风暴结构信息对降水反演的准确性至关重要。DPR的统计量可以作为辐射计算法的数据库，以减少风暴模型的不确定性。如何利用雷达数据中的信息是一个具有挑战性的问题。目前正在研究是否可能利用TRMM的PR数据来改进TMI降雨检索算法中使用的数据库。DPR在GPM中有三个主要角色。它将提供雨结构的三维信息。Ku波段雷达与TRMM降水雷达（PR）类似，但不完全相同。这是从公关角度改进的，改进的必要性有三个方面的原因。首先，GPM核心卫星的拟议轨道约为400公里，高于TRMM的轨道。这就需要提高补偿距离损失增加的灵敏度。设计发射功率由PR的500 W提高到1000 W. (the PR的实际Tx功率结果是大约800 W。第二，轨道倾角约为65度，大于TRMM的35度。由于地球是扁圆形的，卫星在65度轨道上的高度变化超过20公里，远大于35度轨道上的10公里。如果我们使用一个恒定的脉冲重复频率（PRF），如TRMM PR，我们必须使用一个相当小的PRF来吸收雷达回波范围的巨大变化。低PRF将导致低信噪比。敬麦克斯-
This paper outlines the development of the dual-frequency precipitation radar (DPR) to be flown on the Global Precipitation Mission's "core" spacecraft. I. INTRODUCTION In the Global Precipitation Mission (GPM), a dual- frequency precipitation radar (DPR) is planned to be flown on the "core" spacecraft. The "core" spacecraft serves as a high quality reference platform for training and calibrat- ing the rain retrieval algorithms used with the passive mi- crowave radiometers on the other "constellation" satellites. The dual-frequency radar is expected to provide accu- rate estimates of rainfall rate as well as drop size distribu- tion (DSD) parameters from the combination of Ku- and Ka-band radar returns. This paper outlines the present status of the DPR development. Following this introduc- tion, we discuss the critical issues that affect the designing of the DPR. II. DPR REQUIREMENTS A. Relevance of the DPR to GPM The relevance of the DPR to GPM lies in the radar's ca- pability of measuring storm structure, rainfall rates, drop- size distribution (DSD), path-integrated attenuation, and other useful parameters that cannot be obtained by pas- sive sensors. In the latest design, the DPR is composed of Ku-band and Ka-band channels. The Ku-band radar is approxi- mately the same as the TRMM Precipitation Radar (PR) with some improvements. The Ka-band radar provides high sensitivity to light rain and snow. The combination of data from two channels will provide accurate estimates of drop-size distribution parameters. The Ka-band radar will sample the echo data in two different modes simulta- neously. One is a high-sensitivity mode for light rain and snow detection, and the other is a matched-beam mode in which the sampling volumes of Ka- and Ku-band radar channels are matched for collecting dual-frequency echoes from the identical targets. The data collected in the lat- ter mode are used for the estimation of DSD parameters. In the matched-beam mode, a range resolution of 250 m is employed, while in the high-sensitivity mode, a range resolution of 500 m is planned. The current radar design adopts active phased array antennas in both radar chan- nels to make full use of TRMM experience. The DPR will provide three-dimensional information of hydrometeor distribution with high spatial resolution. Such data are very valuable for the study of storm struc- ture. The accurate rainfall estimates from the DPR are expected to be used for calibrating the corresponding esti- mates from the radiometer on the core satellite. The major importance of the DPR, however, lies in the fact that it can provide the regional and seasonal statistics of storm structure together with DSD parameters. Since rain re- trieval algorithms for passive microwave radiometers have to assume a vertical structure of storm either determinis- tically or statistically, reliable storm structure information is crucial for the accuracy of rain estimation. The statis- tics from the DPR can be used as a database in radiometer algorithms to reduce the uncertainties of the storm mod- els. How to utilize the information from radar data is a challenging issue. A possibility of improving the database used in a TMI rain retrieval algorithm by using TRMM's PR data is currently under examination. The DPR has three main roles in GPM. It will provide three-dimensional information of rain structure. The Ku- band radar is similar to, but not exactly the same as, the TRMM Precipitation Radar (PR). It is improved from the PR. The improvement is necessary because of three rea- sons. Firstly, the proposed orbit of the GPM core satellite is about 400 km and higher than the TRMM's orbit. This necessitates the improvement of the sensitivity to com- pensate for the increased range loss. The designed trans- mitting power is increased to 1000 W from PR's 500 W. (the actual Tx power of the PR turned out to be about 800 W.) Secondly, the orbital inclination is about 65 de- grees and larger than the TRMM's 35 degrees. Because of the oblate shape of the Earth, the altitude of the satel- lite changes more than 20 km at a 65-degree orbit which is much larger than 10 km at a 35-degree orbit. If we use a constant pulse repetition frequency (PRF) like the TRMM PR, we have to use a rather small PRF to absorb this large variation of rain echo range from the radar. The low PRF will result in a low signal-to-noise ratio. To max-