SCIENCE CHINA Information Sciences, Volume 63 , Issue 4 : 140304(2020) https://doi.org/10.1007/s11432-019-2800-0

## Deep-learning-based extraction of the animal migration patterns from weather radar images

• AcceptedFeb 16, 2020
• PublishedMar 9, 2020
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### Abstract

Continental coverage and year-round operation of the weather radar networks provide an unprecedented opportunity for studying large-scale airborne migration. The broad and local-scale airborne information collected by these infrastructures can answer many ecological questions. However, extracting and interpreting the biological information from such massive weather radar data remains an intractable problem. Recently, many big-data problems have been solved using the deep learning technology. In this study, the biological information in the weather radar data is identified using the advanced deep learning method. The proposed method consists of two main parts, i.e., a rendering and casting procedure and an image segmentation procedure based on a convolutional neural network. The biological data are automatically extracted by rendering and mapping, image segmentation, and result masking. By analyzing the typical radar data from single and multiple stations, we partly reveal the intensity and speed of the migration pattern. We present the first feasibility study of the extraction of local and large-scale biological phenomena from the Chinese weather radar network data.

### Acknowledgment

This work was supported by National Natural Science Foundation of China (Grant No. 31727901). The authors thank Prof. Kongming WU, Dr. Qiulin WU and Haowen ZHANG, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, for their kindly discussion and useful suggestions. The authors thank Dongli WU and Dasheng YANG, Meteorological Observation Center, China Meteorological Administration, for providing Chinese weather radar data.

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• Figure 1

(Color online) Geometry and volume coverage pattern of weather radar scanning. (a) Scanning strategy and beam geometry of normal weather radar. Five successive elevations are shown. (b) Volume coverage patterns at operational elevations of $0.5^{\circ}$, $1.45^{\circ}$, $2.4^{\circ}$, $3.35^{\circ}$, and $4.3^{\circ}$. When two adjacent elevations overlap, the beams scan the atmosphere with no gap between those elevations.

• Figure 2

(Color online) (a) and (b) Vertical slices of precipitation and biological echoes. (c) and (d) Typical reflectivity factor products of precipitation and biology deduced from the Xuzhou weather radar station. (c) 12:13 UTC on September 27th and (d) 11:41 UTC on August 31st, 2017. Echo types are confirmed by checking the historical weather conditions. From left to right, the subgraphs are scanned at elevations of $0.5^{\circ}$, $1.45^{\circ}$, $2.4^{\circ}$, $3.35^{\circ}$, and $4.3^{\circ}$, with plotting radii of 227, 127, 81, 58 and 45 km, respectively. These radii correspond to a height range of 3000 m (bottom limit of the antenna beam).

• Figure 3

(Color online) Biological echo extraction process. The weather radar data are mapped to grayscale images by a linear mapping method. The biological dataset contains 1500 images for training the convolutional network at each elevation.

• Figure 4

(Color online) DeepLabv3+-based network for extracting the biological information from weather radar. The input resolution is 321 by 321 and the atrous rates in the ASPP part are correspondingly reduced to 6, 8 and 12. The decoder output stride is reduced to 1 for densifying the output feature map.

• Figure 5

(Color online) Training losses and typical segmentation results of the training dataset at each elevation. The training losses are recorded as functions of the number of training steps. The input images are rendered and casted from the weather radar data. The brightness of the input images is linearly related to the radar reflectivity factor. The label images are manually constructed using the MATLAB image segmentation app. The output images are the segmentation results of the trained models. In the label and output images, the black and gray pixels represent the non-biological and biological areas, respectively.

• Figure 6

(Color online) Typical extraction results on different dates. The images in the first row are acquired at an elevation angle of $2.4^{\circ}$, and the brightness is linearly related to the radar reflectivity factor. The images in the second row are the segmentation results of the trained model at the third elevation angle. Biological echoes are found in the red areas.

• Figure 7

(Color online) Large-scale migration pattern in China. (a) Spring; (b) autumn. The red color bar represents the relative migration intensity calculated from the segmentation results (a high red concentration denotes intense migration). The sizes and directions of the arrow represent the average airspeeds and directions, respectively, of the targets passing the radar station. All data are collected at 21:00 local time.

• Table 1   Segmentation performance at each elevation
 Elevation Pixel accuracy mIOU Original (%) Ours (%) Original (%) Ours (%) $0.5^{\circ}$ 94.80 95.30 89.85 90.81 $1.35^{\circ}$ 95.59 95.53 91.28 91.94 $2.4^{\circ}$ 92.63 93.04 86.19 86.91 $3.35^{\circ}$ 92.02 92.37 85.19 85.78 $4.3^{\circ}$ 91.76 92.29 84.59 85.51
• Table 2   Performance comparison between our method and a previous work
 Method Precision (%) Recall (%) F-score (%) Ours 92.6 92.4 92.5 MistNet 72.6 96.1 82.7

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