融合无人机高分辨率DOM和DSM数据语义的崩岗识别

    Benggang recognition on semantic fusion of high-resolution digital orthophoto map and digital surface model data from unmanned aerial vehicle

    • 摘要: 崩岗识别是大规模的崩岗调查、治理和侵蚀机理等研究的首要任务,但以现场调查和人工解译高分辨率卫星遥感影像为主的传统方法,自动化程度低,人力、物力成本高而且效率低,不能满足大范围工作的需要。该研究借鉴遥感影像场景分类识别思路,利用视觉-地形词袋模型(Bag of Visual-Topographic Words, BoV-TW)进行崩岗区域高分辨率数字正射影像图Digital Orthophoto Map(DOM)与数字表面模型Digital Surface Model(DSM)局部特征的混合表达,并通过潜在狄利克雷分配Latent Dirichlet Allocation(LDA)的潜在语义分析融合形成低维度的高层语义表征,最后以支持向量机(Support-Vector Machine, SVM)作为监督学习训练分类器,实现崩岗的高精度快速自动识别。试验结果表明:1)LDA主题个数变化时,该方法总精度可保持在95%左右,崩岗查全率和查准率保持在80%以上,最高分别为97.22%和94.44%;2)视觉-地形词袋词汇表大小变化时,该方法总精度一直在90%以上,最高为96.10%,崩岗查全率也基本在90%以上,最高为100%,崩岗查准率随词汇表大小的增加逐渐提升,最高为85.00%;3)仅使用DOM无法较好地识别崩岗地貌特征,没有合适的特征提取和融合策略,DOM和DSM结合也无法提高崩岗识别效果。同时,该方法时间花费少,效率高,可行性强。该研究可为崩岗调查、监测、治理及侵蚀机理的定量化研究提供参考。

       

      Abstract: Benggang as a fragmented landform type, can be characterized by a deep-cut slope with various shapes and depressions on the vast weathered crust slopes in southern China. Normally, the gully heads have been continuously collapsed to form a typical landform, such as chair-like erosion. Benggang usually develops rapidly due to large amount of erosion, and thereby to threaten land resources and ecological environment. The identification of Benggang development become necessary to control erosion, and then clarify the behind mechanism. However, conventional methods have low levels of automation for a large-scale work, particularly on local inquiry, in-situ search, and manual interpretation for high-resolution images from satellite remote sensing. This paper proposes a novel Bag of Visual-Topographic Words (BoV-TW) model combining high resolution Digital Orthophoto Map (DOM) and Digital Surface Model (DSM) local features to represent Benggang areas, according to the classification and recognition methods in remote sensing images. The local features of DOM can be set in Harris-Affine and Maximally Stable Extremal Regions (MSER), with Scale-Invariant Feature Transform (SIFT) descriptors. The local features of DSM were extracted by a 3D Douglas-Peucker algorithm, representing by gradient direction-invariant descriptors developed in this study. A Latent Dirichlet Allocation (LDA) was used to balance latent semantic analysis, thereby to construct low-dimensional high-level semantic representations. Support Vector Machine (SVM) was used as a supervised learning training classifier to achieve high-precision and fast automatic Benggang recognition. Three Benggang areas in Tongcheng County, Hubei Province were selected as the experimental objects. The original data were collected by DJI Phantom 3 Pro micro UAV in September 2016. Photoscan processing was used to obtain the DOM and DSM of three Benggang areas. Uniform grid division can be used to achieve DOM and DSM tiles in 0.15 m resolution of 256 × 256 pixels. A high-resolution 3D Benggang model was used to mark the areas with/without Benggang. Two Benggang areas were taken as the training set, and the rest were taken as the test set, in three comparative experiments. The results show that: 1) With changing numbers of LDA topics, the proposed method can maintain a total accuracy of 95%, while the recall rate and precision of Benggang 80%, indicating the maximums were 97.22% and 94.44%, respectively. The total accuracy, recall and precision have increased by 12%, 11% and 32%, respectively, compared with that of only DOM features. The recognition performance was significantly improved after combining with DSM features. 2) With changing sizes of the BoV-TW vocabulary, the total accuracy was 90%, and the maximum was 96.10%, while the recall rate reached 90%, the maximum recall rate of 100%. Precision gradually increased as the increase of vocabulary size, with the maximum of 85.00%. Compared with that of only BoV-TW, three performance indicators increased by 13%, 12% and 30%, respectively, indicating that LDA for latent semantic analysis can greatly improve the recognition detection performance. 3) The proposed method was better than that on the ResNet50 network using DOM and DOM + DSM as the data source. It infers that Benggang as a landform type cannot be well recognized using only DOM, or the simple combination of DOM and DSM. Meanwhile, it needs to combine feature extraction and fusion strategy for efficient application. This finding can deliver a useful tool for the quantitative analysis on the identification, control and erosion mechanism for Benggang.

       

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