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Validation and Evaluation of Ocean Calibration Accuracy of FY-3G Precipitation Measurement Radar
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摘要: 年4月发射的风云三号气象卫星G星(FY-3G)是我国首颗专用降水测量卫星, 双频降水测量雷达(precipitation measurement radar, PMR)是该颗卫星上最核心的仪器。基于2023年7月数据, 利用海洋定标理论模型, 模拟海洋表面后向散射截面, 与观测海洋表面后向散射截面进行比对, 实现对PMR定标精度的初步评估。通过与国外星载双频降水测量雷达(global precipitation measurement, dual-frequency precipitation radar, GPM DPR)海洋定标检验结果比对, 评估FY-3G PMR定标的准确性。海洋定标精度检验结果表明: FY-3G PMR Ku波段在入射角小于15°时观测值与模型模拟值的偏差较小, 此时FY-3G PMR的偏差为1.65~2.73 dB, 偏差标准差为0.74~1.82 dB。FY-3G PMR Ka波段在18°入射角时偏差小于0.27 dB, 偏差的标准差为3.49 dB。FY-3G PMR与GPM DPR的定标偏差存在较为固定的偏差, 差异主要源自于数据本身的后向散射统计特性, 各入射角下FY-3G PMR Ku与Ka波段海洋表面后向散射数据稳定性与GPM DPR相当。Abstract: FY-3G precipitation satellite launched in April 2023 is the first dedicated precipitation measurement satellite in China. The dual-frequency precipitation measurement radar (PMR) is the core instrument on the satellite. Because the backscattering performance of the vast ocean area is relatively stable, the calibration accuracy of the on-orbit radar can be tested by studying the backscattering cross-section of the sea surface. FY-3G PMR level 1 data in July 2023 and GPM DPR (global precipitation measurement, dual-frequency precipitation radar) level 2A data are used to analyze the mean value and mean square error of the global sea surface backscattering cross section under no-rain conditions to evaluate the radar performance. At the same time, the theoretical model of ocean surface backscattering is studied to simulate the sea surface backscattering cross-section under the condition of no rain, and the sea surface backscattering cross-section is compared with the actual radar measurement, so as to realize the preliminary evaluation of FY-3G PMR calibration accuracy. Furthermore, the accuracy of FY-3G PMR calibration is evaluated by the ocean calibration test results of GPM DPR data. Test results of ocean calibration accuracy show that when the incidence angle of FY-3G PMR Ku-band is less than 15°, the deviation between the observed value and the model simulation value is small. The deviation of FY-3G PMR ranges from 1.65 to 2.73 dB, while the standard deviation ranges from 0.74 to 1.82 dB. The deviation of FY-3G PMR Ka-band at an 18° incidence is less than 0.27 dB, and the standard deviation of the deviation is 3.49 dB. The calibration deviation of FY-3G PMR and GPM DPR is relatively constant, with the difference is primarily attributed to the backscattering statistical characteristics of the data itself. The stability of the backscattering data of FY-3G PMR Ku- and Ka-band sea surfaces at each incidence angle is comparable to that of GPM DPR. Gas attenuation is not considered at the moment. In the future, the impact of gas attenuation on the Ku- and Ka-band ocean calibration accuracy validation will be further evaluated, and the systematic deviation of FY-3G PMR will be corrected.
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图 1 年7月海洋表面后向散射截面月平均值
Fig. 1 Monthly mean of sea surface backscattering cross section in Jul 2023
图 1 年7月海洋表面后向散射截面月平均值
Fig. 1 Monthly mean of sea surface backscattering cross section in Jul 2023
图 2 年7月FY-3G PMR和GPM DPR 0°入射角下海洋表面后向散射截面统计直方图
Fig. 2 Statistical histogram of sea surface backscattering cross section at 0° incidence angle of FY-3G PMR and GPM DPR in Jul 2023
图 2 年7月FY-3G PMR和GPM DPR 0°入射角下海洋表面后向散射截面统计直方图
Fig. 2 Statistical histogram of sea surface backscattering cross section at 0° incidence angle of FY-3G PMR and GPM DPR in Jul 2023
图 3 年7月FY-3G PMR和GPM DPR海洋表面不同后向散射截面概率
Fig. 3 Probability density of different sea surface backscattering intensity of FY-3G PMR and GPM DPR in Jul 2023
图 3 年7月FY-3G PMR和GPM DPR海洋表面不同后向散射截面概率
Fig. 3 Probability density of different sea surface backscattering intensity of FY-3G PMR and GPM DPR in Jul 2023
图 4 年7月海洋表面后向散射截面月均方差及每轨平均值均方差
Fig. 4 Mean square errors of monthly and orbit mean of sea surface backscattering cross section in Jul 2023
图 4 年7月海洋表面后向散射截面月均方差及每轨平均值均方差
Fig. 4 Mean square errors of monthly and orbit mean of sea surface backscattering cross section in Jul 2023
图 5 年7月FY-3G PMR和GPM DPR不同风速区间的海洋定标结果
Fig. 5 Ocean calibration results of FY-3G PMR and GPM DPR at different wind speed intervals in Jul 2023
图 5 年7月FY-3G PMR和GPM DPR不同风速区间的海洋定标结果
Fig. 5 Ocean calibration results of FY-3G PMR and GPM DPR at different wind speed intervals in Jul 2023
表 1 FY-3G降水测量雷达主要性能指标
Table 1 Main performance indexes of FY-3G PMR
参数 Ku波段 Ka波段 工作中心频率 13.35 ± 0.01 GHz 35.55 ± 0.01 GHz 极化 HH HH 脉冲体制 短脉冲 短脉冲/脉冲压缩 扫描方式 交轨方向一维扫描 交轨方向一维扫描 距离方向观测范围 -5~18 km(海拔) -5~18 km(海拔) 6 dB距离分辨率 ≤ 250 m ≤ 250 m 单程3 dB波束宽度 0.7°±0.02° 0.7°±0.02° 观测刈幅 300 km 300 km 最小可检测降水强度 0.5 mm·h-1 (18 dBZ) 0.2 mm·h-1 (12 dBZ) 辐射精度 ≤ ±1 dB (3σ) ≤ ±1 dB (3σ) 
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表 1 FY-3G降水测量雷达主要性能指标
Table 1 Main performance indexes of FY-3G PMR
参数 Ku波段 Ka波段 工作中心频率 13.35 ± 0.01 GHz 35.55 ± 0.01 GHz 极化 HH HH 脉冲体制 短脉冲 短脉冲/脉冲压缩 扫描方式 交轨方向一维扫描 交轨方向一维扫描 距离方向观测范围 -5~18 km(海拔) -5~18 km(海拔) 6 dB距离分辨率 ≤ 250 m ≤ 250 m 单程3 dB波束宽度 0.7°±0.02° 0.7°±0.02° 观测刈幅 300 km 300 km 最小可检测降水强度 0.5 mm·h-1 (18 dBZ) 0.2 mm·h-1 (12 dBZ) 辐射精度 ≤ ±1 dB (3σ) ≤ ±1 dB (3σ)
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表 2 年7月FY-3G PMR和GPM DPR海洋定标评估结果(Ku波段典型入射角)
Table 2 FY-3G PMR and GPM DPR ocean calibration evaluation results (Ku-band typical incidence angle) in Jul 2023
仪器 入射角/(°) 观测值/dB 模拟值/dB 平均偏差/dB 偏差标准差/dB FY-3G PMR -18 0.37 -2.37 2.74 3.20 -15 3.72 2.07 1.65 1.82 -10 9.33 7.63 1.70 1.68 -5 12.04 10.36 1.68 0.74 0 13.71 11.48 2.23 1.26 5 12.77 10.36 2.41 0.74 10 10.32 7.58 2.73 1.74 15 4.62 2.06 2.55 1.82 18 2.98 -2.38 5.36 3.17 GPM DPR -18 -0.69 -3.39 2.70 3.41 -15 2.65 1.39 1.26 2.08 -10 7.98 7.39 0.59 2.27 -5 11.45 10.39 1.06 1.24 0 12.93 11.63 1.30 1.95 5 11.53 10.45 1.09 1.21 10 8.12 7.49 0.63 2.23 15 2.67 1.54 1.13 2.10 18 -0.58 -3.22 2.64 3.39
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表 2 年7月FY-3G PMR和GPM DPR海洋定标评估结果(Ku波段典型入射角)
Table 2 FY-3G PMR and GPM DPR ocean calibration evaluation results (Ku-band typical incidence angle) in Jul 2023
仪器 入射角/(°) 观测值/dB 模拟值/dB 平均偏差/dB 偏差标准差/dB FY-3G PMR -18 0.37 -2.37 2.74 3.20 -15 3.72 2.07 1.65 1.82 -10 9.33 7.63 1.70 1.68 -5 12.04 10.36 1.68 0.74 0 13.71 11.48 2.23 1.26 5 12.77 10.36 2.41 0.74 10 10.32 7.58 2.73 1.74 15 4.62 2.06 2.55 1.82 18 2.98 -2.38 5.36 3.17 GPM DPR -18 -0.69 -3.39 2.70 3.41 -15 2.65 1.39 1.26 2.08 -10 7.98 7.39 0.59 2.27 -5 11.45 10.39 1.06 1.24 0 12.93 11.63 1.30 1.95 5 11.53 10.45 1.09 1.21 10 8.12 7.49 0.63 2.23 15 2.67 1.54 1.13 2.10 18 -0.58 -3.22 2.64 3.39
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表 3 年7月FY-3G PMR和GPM DPR海洋定标评估结果(Ka波段典型入射角)
Table 3 FY-3G PMR and GPM DPR ocean calibration evaluation results (Ka-band typical incidence angle) in Jul 2023
仪器 入射角/(°) 观测值/dB 模拟值/dB 平均偏差/dB 偏差标准差/dB FY-3G PMR -18 -3.59 -2.30 -1.29 3.51 -15 -0.45 2.06 -2.51 2.00 -10 4.83 7.63 -2.80 2.02 -5 8.28 10.38 -2.10 1.02 0 9.52 11.49 -1.97 1.57 5 8.86 10.38 -1.52 1.02 10 5.33 7.62 -2.29 2.01 15 1.13 2.13 -1.00 2.01 18 -1.98 -2.25 0.27 3.49 GPM DPR -18 -1.72 -2.85 1.13 3.40 -15 1.56 1.73 -0.17 1.99 -10 6.94 7.46 -0.52 2.04 -5 10.09 10.32 -0.23 1.04 0 11.21 11.47 -0.26 1.46 5 10.15 10.35 -0.20 1.03 10 6.90 7.51 -0.61 2.02 15 1.72 1.81 -0.09 1.98 18 -1.44 -2.77 1.33 3.36
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表 3 年7月FY-3G PMR和GPM DPR海洋定标评估结果(Ka波段典型入射角)
Table 3 FY-3G PMR and GPM DPR ocean calibration evaluation results (Ka-band typical incidence angle) in Jul 2023
仪器 入射角/(°) 观测值/dB 模拟值/dB 平均偏差/dB 偏差标准差/dB FY-3G PMR -18 -3.59 -2.30 -1.29 3.51 -15 -0.45 2.06 -2.51 2.00 -10 4.83 7.63 -2.80 2.02 -5 8.28 10.38 -2.10 1.02 0 9.52 11.49 -1.97 1.57 5 8.86 10.38 -1.52 1.02 10 5.33 7.62 -2.29 2.01 15 1.13 2.13 -1.00 2.01 18 -1.98 -2.25 0.27 3.49 GPM DPR -18 -1.72 -2.85 1.13 3.40 -15 1.56 1.73 -0.17 1.99 -10 6.94 7.46 -0.52 2.04 -5 10.09 10.32 -0.23 1.04 0 11.21 11.47 -0.26 1.46 5 10.15 10.35 -0.20 1.03 10 6.90 7.51 -0.61 2.02 15 1.72 1.81 -0.09 1.98 18 -1.44 -2.77 1.33 3.36
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