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Scientia Silvae Sinicae ›› 2021, Vol. 57 ›› Issue (3): 98-107.doi: 10.11707/j.1001-7488.20210310

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Small Object Detection for Infected Trees Based on the Deep Learning Method

Yan Zhou1,Wenping Liu1,*,Youqing Luo2,Shixiang Zong2   

  1. 1. College of Information, Beijing Forestry University Beijing 100083
    2. College of Forestry, Beijing Forestry University Beijing 100083
  • Received:2019-10-17 Online:2021-03-01 Published:2021-04-07
  • Contact: Wenping Liu

Abstract:

Objective: The recognition of forest images taken with the unmanned aerial vehicle (UAV) It is an the important technology using the unmanned aerial vehicle (UAV) images for pest automatic monitoring and early warning tree recognition for the automatic pest-control warning system in a forestry. An approach on object detection based on deep learning was used to accurately recognize and locates small-scale infected trees in high-resolution forest UAV images are accurately recognized and located through deep learning object detection technology. Method: The images of pine forest infected by Dendroctonus valens from Liaoning Province were chosen used as the experimental data. The UAV forest image dataset was constructed by images taken from the a height of 180-240 m and annotated by open source software LabelImg. Because the instance size of UAV forest images dataset in this paper is far smaller than general datasets, a small infected trees detector (SITD) is designed to improve the ability of recognition and localization for small object, since the instance size of UAV forest images dataset in this paper is far smaller than general datasets. Firstly, based on the framework of single shot multi-box detector (SSD), the prediction module is built from conv3_3 and tailored according to the size of the target tree in the image, then the generation method of default boxes is optimized. Secondly, the base feature map is transformed into the enhanced feature map by the feature enhance module, thus generating the base and enhanced prediction module are generated by using base feature maps and enhanced feature maps which is transferred by the feature enhance module. Finally, dual loss functions are used to facilitate the feature learning. Result: The method of small object detection based on deep learning can realize UAV remote monitoring of for forest pests, and accurately detect small and dense infected trees in UAV images accurately. In this paper, five SITD models with different structures and other object detection frameworks as SSD, FSSD and RFBNet are used to trained and tested with on UAV forest image dataset, were compared by and average precision (AP) and Precision-Recall curve are selected as evaluation indexes. The proposed method achieves the average precision of 92.62% using the UAV images captured in our study, which gets a gain of 69.71% compared to the original SSD300, and higher than the other three frameworks. Conclusion: Experimental results demonstrate that the method of small object detection based on deep learning can realize automatic detection of infected trees, and simplify the monitoring process for forest pests, and which can improve the warning ability of forest pests.

Key words: unmanned aerial vehicle imagery, forest pest, deep learning, object detection

CLC Number: