王丽美, 靳国旺, 熊新, 武珂, 黄启灏. 耕地细碎化农业区冬小麦遥感制图方法[J]. 农业工程学报, 2022, 38(22): 190-198. DOI: 10.11975/j.issn.1002-6819.2022.22.021
    引用本文: 王丽美, 靳国旺, 熊新, 武珂, 黄启灏. 耕地细碎化农业区冬小麦遥感制图方法[J]. 农业工程学报, 2022, 38(22): 190-198. DOI: 10.11975/j.issn.1002-6819.2022.22.021
    Wang Limei, Jin Guowang, Xiong Xin, Wu Ke, Huang Qihao. Winter wheat mapping in land fragmentation areas using remote sensing data[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2022, 38(22): 190-198. DOI: 10.11975/j.issn.1002-6819.2022.22.021
    Citation: Wang Limei, Jin Guowang, Xiong Xin, Wu Ke, Huang Qihao. Winter wheat mapping in land fragmentation areas using remote sensing data[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2022, 38(22): 190-198. DOI: 10.11975/j.issn.1002-6819.2022.22.021

    耕地细碎化农业区冬小麦遥感制图方法

    Winter wheat mapping in land fragmentation areas using remote sensing data

    • 摘要: 从遥感影像中提取作物播种面积和空间分布对耕地可持续发展和粮食安全意义重大。目前的遥感小麦制图研究主要依靠光学图像和高复杂度的分类方法,且现有分类算法在小样本条件下、耕地细碎化农业区的分类性能以及时间迁移性能仍然不确定,探索适合小样本的低复杂度的稳定算法具有现实意义。该研究基于Google Earth Engine(GEE)遥感云平台,使用Sentinel-1 SAR和Sentinel-2光学时间序列遥感数据,评估了时间加权动态时间规整算法(Time-Weighted Dynamic Time Warping,TWDTW)、随机森林算法(Random Forest,RF)和基于相似性测度(Difference and Similarity Factor,DSF)的OTSU阈值法在小样本条件下、耕地细碎化农业区的冬小麦制图精度和时间迁移性能。研究结果表明,在有限样本条件下,TWDTW方法小麦制图精度最高,总体精度(Overall Accuracy,OA)和Kappa系数分别为0.923和0.843;其次是RF(OA=0.906,Kappa=0.809)和DSF算法(OA=0.887,Kappa=0.767);基于欧式距离的OTSU阈值法分类精度最低。当利用算法进行时间迁移分类提取2021年的冬小麦分布图时,TWDTW和DSF算法表现出更好的稳定性且分类精度优于RF算法,其中TWDTW算法的精度最高,OA和Kappa系数分别为0.889和0.755;RF算法分类精度下降明显,OA和Kappa系数分别降低了约0.07和0.19,说明RF算法的迁移分类性能较差。综合来看,TWDTW算法对样本和耕地细碎化的敏感性较低,可以在有限样本条件下实现耕地细碎化农业区的高精度连续冬小麦制图;而RF算法对样本和耕地细碎化的敏感性较高,在有限样本条件下的耕地细碎化农业区进行连续冬小麦制图时稳定性较差。

       

      Abstract: Abstract: An accurate and rapid extraction can be highly required for the crop sown area and spatial distribution from the remote sensing images, particularly for the sustainable development of cultivated land and food security. However, winter wheat mapping using remote sensing depends mainly on optical images and complex classification at present. Besides, it is still unclear on the classification performance and time-transferring capability of existing classification with the small sample sets in the highly land-fragmentation areas. The fragmentation of cultivated land has always been the core of rural land regulation, where the land resources are wasted to reduce the cultivated land productivity in the soil fertility with the high production costs. The difficulty of crop mapping in finely fragmented areas is generally higher than that in large-scale farming areas. The applicability and stability are very important for the study of such areas. It is necessary to realize long-term large-scale crop mapping with a low dependence on the number of samples and high efficiency. Therefore, it is of practical significance to develop a new extraction with a low complexity suitable for small samples. Previous studies have shown that the accuracy of crop mapping using single-phase satellite imagery cannot fully meet the high requirement in recent years, especially in land fragmentation areas. In this study, the high-level fragmentation of cultivated land was selected as the study area in the Wancheng District, Nanyang City, China. Using the Google Earth Engine cloud computing and Sentinel-1 SAR and Sentinel-2 optical images, three advanced classifications were evaluated, including the time-weighted dynamic time warming (TWDTW), random forest (RF), and OTSU with distance measure (DSF), for the winter wheat mapping accuracy and time-transferring capability with the small sample sets in the study area. The results show that effective extraction was achieved in the sown area and spatial distribution of winter wheat in 2020, but there were some differences in the classification accuracies. The TWDTW presented the highest classification accuracy, with the Overall Accuracy (OA) and Kappa coefficients 0.923 and 0.843, respectively, followed by the RF (OA=0.906, Kappa=0.809) and DSF (OA=0.887, Kappa=0.767). The OTSU with the Euclidean Distance showed the lowest classification accuracy. When transferring to extract the winter wheat classification maps of 2021, the classification accuracy of each model decreased: The TWDTW and DSF showed better stability and classification accuracy than the RF. The TWDTW shared the highest accuracy with the OA and Kappa of 0.889 and 0.755, respectively. The classification accuracy of RF decreased significantly, and the OA and Kappa decreased by about 0.07 and 0.19, respectively, indicating the lower stability of the model. In general, the TWDTW presented low sensitivity to the training samples and spatial heterogeneity. As such, the high-precision continuous mapping was realized for the winter wheat in the agricultural areas with high spatial heterogeneity under the condition of limited samples. However, the RF was sensitive to the training samples and spatial heterogeneity. The condition of limited samples can cause low stability in the continuous winter wheat mapping in high spatial heterogeneity agricultural areas. This finding can provide important selection ideas and scientific support for continuous crop mapping with the small sample sets in the highly land-fragmentation areas.

       

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