Using doppler weather radar to monitor the first generation of migrating Mythimna separata (Walker) in Beijing in 2013
Author of the article:LIU Fan, ZHANG Zhi, LIN Pei-Jiong, LI Xiang-Rui, JIAO Re-Guang, HU Gao, ZHANG Yun-Hui
Author's Workplace：College of Plant Protection, Nanjing Agricultural University, Nanjing 210095, China
Key Words：Mythimna separata; migration; doppler weather radar; echoes; reflectivity; monitoring and forecasting
Abstract：
[Objectives] To obtain the characteristics of the migrating Mythimna separata (Walker) during the peak migration episode in 2013 from the doppler weather radar echoes, and explore the relationship between the numbers resolved from radar echoes and the catch sizes from search light traps, which would provide a foundation to monitor insect migration with doppler weather radar. [Methods] The CINRADSA weather radar data in Beijing and the interval catch sizes from searchlight trap during the migrating peak days of the first generation moths of M. separata in 2013 were selected, and the weather radar data were extracted, retrieved, calculated, counted, analyzed and visualized with some libraries in Python and R. [Results] The number of the M. separata moths from searchlight trap at Yanqing accounted for more than 80% every night from 5th to 9th in June, and the reflectivity between 15 dBZ and 15 dBZ of the echoesfrom the insect swarms above the monitoring site was more than 90%, of which the number of radar echoes from 0 to 15 dBZ accounted for 30.7%, 42.0%, 43.2%, 37.2% and 25.1%, respectively, the trend was similar with the proportion of the M. separata moths from searchlight trap. The direction of the target echoes was northward on average from 5th to 8th in June and southward on 9th. The proportion of echoes with northward direction has the similar trend with the proportion of the M. separata moths from searchlight trap, and the correlation coefficient between them is 0.95. The average speed of the northward echoes from 5th to 8th is close to the wind speed, however the displacement speed is 1.36 m/s on the 9th, which is close to its own flight speed. The number of the M. separata moths retrieved from weather radar data was positively linearly correlated with the number of the M. separata moths from searchlight trap. The maximum of M. separata moths flying over Beijing within the radar monitoring range (approximately 4 300km2) in one night reached to 6 million heads, and the total mass was more than 0.8 tons. [Conclusion]Doppler weather radar can observe the characteristics of the migrating M. separata moths during the peak episode, and these parameters help in understand the migration of M. separata.