Airborne Field Campaign Results of Ka-band Precipitation Measuring Radar in China
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摘要: 2010年6—10月在天津与江苏地区开展了国内首次Ku/Ka频段星载降水测量雷达机载校飞试验。此次校飞试验获得了宝贵的机载雷达观测数据和地面、海面同步观测数据,目前已开展了外定标、数据对比与衰减订正等工作。该文给出了天津校飞试验中Ka频段降水测量雷达实测结果,对Ka频段降水测量雷达资料与天津地区S波段地基多普勒雷达资料进行了详细的对比分析,有利于更好地了解Ka频段降水测量雷达仪器本身的性能及其探测降水的能力;利用由GPS探空资料、地基多通道微波辐射计观测亮温结合微波辐射传输模式得到的雷达路径积分衰减量,对Ka频段降水测量雷达进行了衰减订正,为继续开展降水反演工作奠定了基础。Abstract:
Spaceborne precipitation measuring radar can measure precipitation quantitatively, observe the vertical distribution and provide three dimensional precipitation structures. Spaceborne precipitation measuring radar is an important instrument on FY-3 meteorological satellite constellation. As a possible future member of the Global Precipitation Measurement (GPM), this satellite will carry dual-frequency precipitation radar operating at Ku and Ka bands to provide scientific data for dual-frequency retrieval algorithm. Its two prototype devices, Ku-band and Ka-band radars have already been developed under the support of National Defense Science and Industry Bureau. Field campaign of Ku/Ka-band airborne precipitation measuring radar is carried out by National Satellite Meteorological Center of China Meteorological Administration combining several groups from June to October in 2010 in Tianjin and Jiangsu, called BH-RM 2010 and JS-RM 2010, respectively. This is the first time that China carries out airborne precipitation measuring radar field campaign. The purposes of this field campaign are to validate the correctness of internal and external calibration scheme under airborne conditions, observe simultaneously with ground-based radar and microwave radiometer and compare satellite-airplane-ground observation data, validate the functionality and performance of precipitation measuring radar, and explore data processing and retrieval algorithms of precipitation measuring radar. Numerous data are obtained from various instruments in the field campaign, including airborne precipitation measuring radar, ground-based weather radar, ground-based multi-channel microwave radiometer, GPS radiosonde, 10 GHz and 37 GHz radiometer, portable wind measuring device, and temperature measuring device. Initial analysis is accomplished with observation data obtained from BH-RM 2010. Observation results of Ka-band precipitation measuring radar working in pulse compression mode and short pulse mode are presented, which show clearly the vertical and horizontal structure of rainfall. Due to the radar different scan modes, resolutions, frequencies, and dynamic range, it's difficult to compare airborne radar data and ground-based radar data accurately, and the unstable attitude of the airplane makes the comparison more difficult. Spatial matching of Ka-band airborne radar data and Tianjin S-band ground-based Doppler radar data is carried out and detailed procedures are introduced. Quantitative indexes are further computed to indicate the observation consistency statistically. In rain retrieval algorithms, attenuation correction is a critical step. Using GPS radiosonde data, ground-based multi-channel microwave radiometer data and microwave radiative transfer model, the integrated attenuation of Ka-band radar is computed and attenuation correction is accomplished. The result is reasonable, which lays a basis for future rain retrieval. Data obtained by various instruments in the field campaign will be analyzed thoroughly, propelling development and rain rate retrieval of our spaceborne precipitation measuring radar.
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表 1 Ka频段机载降水测量雷达的主要参数
Table 1 Main parameters of Ka-band airborne precipitation measuring radar
参数 参数值 飞行高度 约9 km 工作频率 35.5 GHz 天线尺寸 1.4 m×0.8 m 波束宽度 0.9° 采样点数 80 扫描角度 ±18° 测绘带宽 约5.8 km 脉冲宽度 20 μs,2.33 μs,1.2 μs 距离分辨率 200 m,350 m,180 m 水平分辨率 140 m 表 2 匹配数据的各项指标
Table 2 Indexes of match data
统计量 2010-07-10 2010-07-10 2010-08-05 Ka雷达 SA雷达 Ka雷达 SA雷达 Ka雷达 SA雷达 观测时间 01:56 01:54 02:21 02:24 01:53 01:54 最大值/dBZ 29.0555 28.0000 26.1907 26.0000 28.9097 16.0000 最小值/dBZ -9.3367 -3.0000 -8.8639 -4.0000 1.0491 1.0000 平均值/dBZ 21.3517 16.4537 15.5933 11.6657 21.7788 11.9742 均方根误差/dBZ 9.5053 8.1828 9.1133 -
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