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基于资源三号卫星影像的茶树种植区提取

Extracting tea plantations based on ZY-3 satellite data

  • 摘要: 茶是世界上饮用最多、影响最广的天然植物饮料,在人类的日常生活中起到重要的作用,为了能有效管理茶叶种植,为政策制订提供依据,很有必要获取准确的茶园空间分布信息。该文以浙江省松阳县的樟溪乡、斋坛乡、叶村乡、竹源乡为研究区域,探讨基于资源三号(ZY-3)卫星数据的茶树种植区提取方法。选用2012年12月25日和2013年6月9日的ZY-3影像,采用决策树提取方法,根据研究区域内茶树的种植方式、生长情况等差异,分平原区和山区进行研究,使用光谱特征和植被覆盖指数(normalized difference vegetation index,NDVI)时相差异作为平原区茶树种植区提取特征,山区则添加了方向强度的纹理特征,以地面验证点为参考,对提取结果进行了精度评价,同时与神经网络(NN)分类结果进行比较。结果表明,决策树方法结合光谱信息和纹理信息,可有效提高茶园提取精度:平原区的总体精度为95.00%,Kappa系数为0.85,与NN分类相比分别提高了5.46%、0.19,山区茶树种植区提取的总体精度为92.97%,Kappa系数为0.69,与NN分类相比分别提高了7.57%、0.61,该研究可为政府部门进行茶叶估产及灾害预防处理等提供一定的参考。

     

    Abstract: Abstract: Tea is the most consumed natural plant drink in the world, and it plays an important role in human's daily life. The spatial distribution information of tea plantation is helpful for the government management and decision-making. Songyang county is located in southwest part of Zhejiang province, China, and the topography is characterized by basin in the central and surrounded by hills and mountains. The humid and cloudy climate is very suitable for tea planting, which accounts for the large proportion of tea plantation area, 68.5% of county’s whole cultivated land. In this paper, ZhangXi Town, ZhaiTan Town, YeCun Town and ZhuYuan Town of SongYang County in Zhejiang Province were chosen as study area, and ZY-3 satellite images acquired on December 25, 2012 and June 9, 2013 were used to study the method of tea plantations extraction. Eight categories including roads, water, buildings, shadows, bare soil, forest, other crops and tea plantation were identified after conducting visual interpretation and field surveys. The decision tree method was adopted to extract the tea plantations. Due to the fact that tea plants in plain areas and mountains areas show different characteristics in their planting patterns, planting area and growth status, ,the decision trees were built separately for these two different areas.The threshold values in the decision tree were determined by gradually changing their values in a certain range. Spectral curve analysis shows the range of the difference between band4 (0.77-0.89 μm) and band3 (0.63-0.69 μm) on December 25, 2012 is 20-30. The normalized difference vegetation index (NDVI) is almost unchanged or decreased from summer to winter for forest lands as they are covered mainly by evergreen broad-leaved forest, deciduous broad-leaved forest, bamboo forest and mixed forest. As for tea plant, due to its seasonal harvest and pruning in summer, NDVI in summer is a little lower than that in winter and the threshold value of NDVI difference between summer (June 9, 2013) and winter (December 25, 2012) was 0~0.1. As tea plants are terraced planted along the contour in mountain area, texture features characterized with nearly parallel line trend for tea plantations are presented in the image. The panchromatic data on December 25, 2012 was used to derive texture features. Anisotropic strength with a range of 0 to 1 was obtained after conducting the anisotropic strength algorithm. The classification results with different threshold values were compared with region-of-interest data and threshold values with the highest overall accuracy and Kappa coefficient were selected as final threshold. For plain areas, the difference between band4 and band3 was used to roughly exclude roads, water, buildings, bare soil, other crops and part of the forest from tea plantations with the value above 26. Then the threshold value of 0 for NDVI difference between summer and winter was adopted to exclude the remaining forest. Spectral feature and textural feature were both used to extract tea plantations in mountainous areas. The threshold value of 20 for band4 and band3 difference and 0 for NDVI difference between summer and winter were firstly adopted to exclude water, buildings, crops, roads, bare soil and part of forest. And the threshold of 0.35 for anisotropic strength was then adopted to exclude the remaining forest. The classification maps were validated with ground verification data and compared with results derived from neural network (NN) classification. The results show that decision tree method combining with spectral and textural information can significantly improve the classification accuracy. The overall accuracy and Kappa coefficient in the plain area were 95.00% and 0.85, respectively, increased by 5.46% and 0.19 when compared with NN classification. The overall accuracy and Kappa coefficient in the mountain area were 92.97% and 0.69, respectively, increased by 7.57% and 0.61 when compared with NN classification. The presented study could provide a reference for government forecasting crop production and preventing disaster for tea plantation.

     

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