Quality Control and Evaluation on Non-cloud Echo of Ka-band Cloud Radar

Zeng Zhengmao; Zheng Jiafeng; Yang Hui; Zheng Min; Zeng Yingting

doi:10.11898/1001-7313.20210307

Vol.32, NO.3, 2021

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Article Navigation > Journal of Applied Meteorological Science > 2021 > 32(3): 347-357

Zeng Zhengmao, Zheng Jiafeng, Yang Hui, et al. Quality control and evaluation on non-cloud echo of Ka-band cloud radar. J Appl Meteor Sci, 2021, 32(3): 347-357. DOI: 10.11898/1001-7313.20210307.

Citation:

Zeng Zhengmao, Zheng Jiafeng, Yang Hui, et al. Quality control and evaluation on non-cloud echo of Ka-band cloud radar. J Appl Meteor Sci, 2021, 32(3): 347-357. DOI: 10.11898/1001-7313.20210307.

Zeng Zhengmao, Zheng Jiafeng, Yang Hui, et al. Quality control and evaluation on non-cloud echo of Ka-band cloud radar. J Appl Meteor Sci, 2021, 32(3): 347-357. DOI: 10.11898/1001-7313.20210307.

Citation:

Zeng Zhengmao, Zheng Jiafeng, Yang Hui, et al. Quality control and evaluation on non-cloud echo of Ka-band cloud radar. J Appl Meteor Sci, 2021, 32(3): 347-357. DOI: 10.11898/1001-7313.20210307.

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Quality Control and Evaluation on Non-cloud Echo of Ka-band Cloud Radar

DOI: 10.11898/1001-7313.20210307

1.
Fujian Meteorological Information Center, Fuzhou 350001
2.
Fujian Key Laboratory of Severe Weather, Fuzhou 350001
3.
Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu 610225
4.
Fujian Meteorological Service Center, Fuzhou 350001

Received Date: 2020-11-06
Rev Recd Date: 2021-01-18
Publish Date: 2021-05-31

Abstract

Abstract

Aiming at non-cloud echoes in Ka-band millimeter wave cloud radar observation, an improved data quality control method is proposed. Using the observation at Pinghe of Fujian from September 2018 to August 2020, the quality of the radar is quantitatively evaluated to study the actual impact of data quality control on cloud-precipitation detection. The non-cloud echoes show the characteristics of weak radar reflectivity factor (Z) and strong depolarization ratio (R) at Pinghe. But statistics show that there is difference from those of Qinghai-Tibet Plateau or Guangdong. Therefore, using the radar reflectivity factor (Z) less than -5 dBZ and linear depolarization ratio (R) greater than -22 dB as the judgment condition, and with the aid of filtering, non-cloud echoes can be effectively filtered. At the same time, a typical example is used to verify the effectiveness of the algorithm. Non-cloud echoes have a significant effect on the detection of cloud below 3 km, especially weak echoes. Non-cloud echoes account for 9.20% of all radar reflectivity factor samples, and 34.05% of all radar linear depolarization ratio samples. For the weak echo below -5 dBZ, the impact of non-cloud echoes is more significant, which accounts for 67.20% of all radar reflectivity factor sample. The detection rate of non-cloud echoes matter is closely related to the radar sensitivity, and the overall decrease with the height increaseing. The detection rate of non-cloud echoes decreases with the height increaseing. Meanwhile, non-cloud echoes have a certain relationship with the boundary layer, with an obvious diurnal change trend. From afternoon to midnight, due to strong turbulent activity, the detection rate of non-cloud echo matter is also higher, and the peak occurs at 1700 BT. From midnight to sunrise, due to the weakening of turbulent motion, the detection rate of non-cloud echo gradually decreases, and the lowest value occurs at 0400 BT. Non-cloud echoes have a significant effect on the vertical distribution of cloud precipitation. After quality control, the number of samples at the height of 0.12-2.5 km for radar reflectivity factor decrease by 17.68%, and the number of samples at the height of 0.12-4 km for radar linear depolarization ratio decrease by 14.29%.
- millimeter wave cloud radar;
- non-cloud echo;
- quality control;
- effect evaluation

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Figures and Tables

Fig. 1 Probability distribution of measured Z and R of non-cloud and cloud-precipitation echoes observed by Pinghe radar in Fujian from Sep 2018 to Oct 2020

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Fig. 2 Frequency distributions of measured Z and R below 3 km altitude before and after quality control observed by Pinghe radar in Fujian from Sep 2018 to Aug 2020

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Fig. 3 Time-height frequency distributions of non-cloud echoes and frequency distribution of the whole levels observed by Pinghe radar in Fujian from Sep 2018 to Aug 2020

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Fig. 4 Frequency-height distributions of measured Z and R of non-cloud echoes before and after quality control observed by Pinghe radar in Fujian from Sep 2018 to Aug 2020

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Fig. 5 Comparison of low altitude cumulus cloud and deep convective precipitation cloud echoes before and after radar quality control observed by Pinghe radar in Fujian from 1200 BT to 2000 BT on 18 Apr 2019

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Fig. 6 Comparison of low altitude stratus clouds, cumulus and high altitude cirrocumulus echoes before and after quality control of observed by Pinghe radar in Fujian from 1700 BT to 2300 BT on 19 May 2019

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Fig. 7 Comparison of low altitude cumulus cloud and weak convective precipitation cloud echoes before and after quality control observed by Pinghe radar in Fujian from 1500 BT to 2300 BT on 2 Sep 2018

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Table 1 Major performance parameters for Ka-band millimeter wave cloud radar

参数	数值
工作频率	35 GHz±500 MHz
波束宽度	0.4°
脉冲重复频率	5988~16666 Hz
峰值功率	20 W
时间分辨率	1 min
空间分辨率	30 m
观测资料	Z/V/σ_V/R
信号处理方式	FFT

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Table 2 Major parameters of 4 detection modes

参数	边界层模式	中云模式	高云模式	降水模式
脉冲宽度/μs	0.2	8	24	0.2
脉冲重复频率/Hz	16666	8333	5988	5988
驻波时间/s	0.98	1.97	1.37	1.37
相干积累数	4	2	1	1
非相干积累数	16	32	32	32
FFT点数	256	256	256	256
距离分辨率/m	30	30	30	30
有效探测高度/km	0.12~7.5	1.47~7.5	3.87~20	0.12~20
最大不模糊速度/(m·s^-1)	8.93	8.93	12.83	12.83
速度分辨率/(cm·s^-1)	6.98	6.98	10.02	10.02

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