基于GF-3全极化SAR影像多特征优选的水产养殖塘提取

    Extracting aquaculture pond using multi-feature optimization of GF-3 PolSAR Imagery

    • 摘要: 高分三号作为中国首颗民用高分辨率多极化合成孔径雷达卫星,为水产养殖用地监测提供了重要的数据源。为了充分利用GF-3 全极化SAR影像,该研究提出了一种基于特征优选的全极化SAR影像养殖塘提取方法。首先通过极化分解和灰度共生矩阵方法共获取了55维特征;然后对影像进行多尺度分割,并利用随机森林-递归特征消除(Random Forest-Recursive Feature Elimination,RF-RFE)算法进行特征优选;最后基于最优特征集进行随机森林分类提取了养殖塘。以南京固城湖和东台近海两个典型区为研究区,利用GF-3 全极化数据进行养殖塘提取试验,结果表明,与单一极化分解方法相比,综合利用多种极化特征在一定程度上提高了总体分类精度,但仍然难以区分养殖水体和非养殖水;经过特征优选,香农熵SE及其强度分量SE_I对于养殖塘识别是很好的极化参数,而纹理特征Variance的引入有效减少了养殖水体和非养殖水体的错分;该研究方法与最大似然和支持向量机相比,总体精度最高,固城湖区域和东台近海区域分别为96.85%和94.60%,研究结果可为GF-3卫星在水产养殖塘提取方面的应用提供参考。

       

      Abstract: Abstract: Artificial aquaculture ponds have been mainly distributed in the coastal and inland areas of China in recent years, particularly with the continuous growth of the population and the ever-increasing demand for food. Aquaculture can inevitably pose a series of environmental degradation on a large number of wetlands, soil, and water bodies in ecosystems. Therefore, it is necessary to monitor the distribution and spatiotemporal evolution of aquaculture land, especially for the decision-making on the resource management and the expanding reproduction of fishery. A traditional survey cannot fully meet the high requirements of monitoring in large-scale aquaculture, due to the time-consuming and labor-intensive tasks. In this study, a feature-optimized extraction was proposed for the culture pond using the full-polarization SAR images. Two study areas were selected in the Gucheng Lake area of Nanjing and the offshore area of Yancheng Dongtai in Jiangsu Province of China. The fully polarimetric GF-3 data was used as the data source. 1) 47 polarization features of GF-3 data were obtained using a variety of polarimetric target decomposition, and 8 texture features were extracted using the gray level co-occurrence matrix, according to the Shannon Entropy (SE) polarization feature. All features were merged into one multi-channel image. 2) The multi-channel image was divided into numerous image objects by multiresolution segmentation. 3) The Random Forest-Recursive Feature Elimination (RF-RFE) was applied for the feature selection. 4) An object-oriented random forest was used to extract the aquaculture ponds. Three combined strategies and two classifications were selected to evaluate the new model, including the Freeman polarization decomposition, H/A/α polarization decomposition, and the 47-dimensional optimal polarization without texture features, as well as the Maximum Likelihood (MLC), and Support Vector Machine (SVM). Four strategies of feature combination and three classifications were designed to finally obtain 12 sets of classification. The experimental results show that the accuracy of the random forest was higher than that of MLC and SVM, in terms of the classifier. The feature combination presented the highest accuracy, where the three-dimensional features were selected as SE, SE_I, and Variance, indicating a better performance than that for the feature combination of single-polarization decomposition without texture introduction. Therefore, the features after polarization decomposition could greatly contributed to representing the difference between ground objects, particularly with the higher classification accuracy than before. The texture feature with the Variance was greatly improved the classification accuracy of polarization features. In the Gucheng Lake area, the overall accuracy was 96.85%, and the Kappa coefficient was 0.95. In the coastal area of Dongtai offshore, the overall accuracy was 94.60%, the Kappa coefficient was 0.92. Consequently, the user and mapping accuracies were 94.44%, and 95.07%, respectively, indicating the better universality and stability of the new model for the identification of aquaculture ponds in various breeding modes. More importantly, the GF-3 satellite imagery can be widely expected to apply for the extraction of aquaculture ponds.

       

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