Jin Ziqi, Wang Xinmin, Bao Yansong, et al. Squall line identification method based on convolution neural network. J Appl Meteor Sci, 2021, 32(5): 580-591. DOI:  10.11898/1001-7313.20210506.
Citation: Jin Ziqi, Wang Xinmin, Bao Yansong, et al. Squall line identification method based on convolution neural network. J Appl Meteor Sci, 2021, 32(5): 580-591. DOI:  10.11898/1001-7313.20210506.

Squall Line Identification Method Based on Convolution Neural Network

DOI: 10.11898/1001-7313.20210506
  • Received Date: 2021-03-01
  • Rev Recd Date: 2021-05-12
  • Publish Date: 2021-09-30
  • Squall line often leads to heavy rain, gale and hail, which is a difficult key problem in nowcasting. In order to explore the feasibility of deep learning for squall line identification, the training, validation and test set sample sets are established based on the radar data of Zhengzhou and Zhumadian in Henan Province during 2008-2020. The convolutional neural network (CNN) algorithm is used to construct a squall line identification model. The critical success index (CSI), equitable threat score (ETS), hit rate (POD) and false positive rate (FAR) are used to quantitatively evaluate the identification effect of the model. The influence of different sample composition and network structure on squall line identification effect are compared. The results show that the composition ratio of sample is imbalanced, because squall line accounts for very small proportion in all kinds of weather processes. This imbalance will degrade the classification performance of the identification model to squall line samples. The imbalance of sample composition can be improved by changing sampling mode and optimizing network structure, both can improve the identification efficiency, especially the latter. However, the combination of the two methods does not bring further improvement. The over fitting problem in network training can be alleviated by increasing the sparsity and randomness of the network structure. The validation set shows that CSI is 0.87, ETS is 0.82, POD is 0.96, and FAR is 0.10. Based on the test set, the echo can be correctly identified by network as non-squall line in the weak stage of convection development, and as squall line in the strong stage of squall line development. The echo intensity and spatial distribution of squall line cases differ greatly, and the samples in the test set have the image features which are not included in the training set, and therefore the identification effect reduces. The test set show that CSI is 0.66, ETS is 0.58, POD is 0.86, and FAR is 0.24. The research reveals that CNN can extract and learn the image features of squall line echo, and it has a certain ability to identify squall line.
  • Fig. 1  Identification results of squall line detected by Zhengzhou radar on 26 Jun 2018

    Fig. 2  Identification results of squall line detected by Zhumadian radar on 3 Jun 2019

    Fig. 3  Identification results of squall line detected by Zhengzhou radar on 24 Jun 2020

    Table  1  Occurrence time of squall line processes

    序号 时间 序号 时间
    1 2008-05-09T06:00—11:00 12 2014-07-29T05:00—22:00
    2 2008-06-03T07:00—11:00 13 2015-07-14T12:00—15:00
    3 2009-05-16T12:00—15:00 14 2016-06-04T16:00—22:00
    4 2009-06-03T11:00—16:00 15 2016-06-05T09:00—16:00
    5 2009-06-14T11:00—16:00 16 2016-06-13T14:00—22:00
    6 2011-07-26T08:00—16:00 17 2017-05-22T10:00—13:00
    7 2013-06-02T10:00—14:00 18 2018-06-10T10:00—14:00
    8 2013-07-04T06:00—13:00 19 2018-06-13T05:00—09:00
    9 2013-07-31T20:00—24:00 20 2018-06-26T06:00—13:00
    10 2013-08-01T08:00—16:00 21 2019-06-03T12:00—15:00
    11 2013-08-11T09:00—18:00 22 2020-06-24T11:00—16:00
    DownLoad: Download CSV

    Table  2  Criteria of squall line discrimination

    相关文献 判别依据
    文献[22] ①大于12 dBZ的回波带不小于150 km,持续时间超过5 h;②大于36 dBZ的回波带长宽比不小于3:1
    文献[23] ①大于20 dBZ的回波带不小于100 km,持续时间超过4 h;②大于40 dBZ的回波带长宽比不小于5:1,持续时间超过2 h
    文献[24] ①大于40 dBZ的回波带呈连续或准连续且不小于100 km,持续时间超过3 h;②线性或准线性对流共有一个回波前缘
    文献[25] 大于35 dBZ的回波带长宽比大于5:1,且长度大于50 km
    文献[9] ①由层云(15 dBZ)连接的对流云(40 dBZ)组成的系统长轴大于100 km,持续时间超过4 h;②系统长宽比大于5:1,持续时间超过2 h
    DownLoad: Download CSV

    Table  3  Information of datasets

    数据集 飑线样本量 非飑线样本量 总样本量
    训练集 1319 3035 4354
    验证集 439 1011 1450
    测试集 309 1075 1384
    DownLoad: Download CSV

    Table  4  Identification result of different schemes

    方案 CSI ETS POD FAR
    原方案 0.59 0.47 0.77 0.27
    过采样 0.65 0.52 0.80 0.26
    降采样 0.74 0.63 0.93 0.23
    网络结构优化 0.87 0.82 0.96 0.10
    降采样及网络结构优化 0.88 0.83 0.97 0.10
    DownLoad: Download CSV

    Table  5  Comparison of training sets

    训练集 飑线样本量 非飑线样本量 总样本量
    原训练集 1319 3035 4354
    过采样 2638 3035 5673
    降采样 1319 2035 3354
    DownLoad: Download CSV

    Table  6  Identification results of validation set and test set

    数据集 CSI ETS POD FAR
    验证集 0.87 0.82 0.96 0.10
    测试集 0.66 0.58 0.86 0.24
    DownLoad: Download CSV
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    • Received : 2021-03-01
    • Accepted : 2021-05-12
    • Published : 2021-09-30

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