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全文摘要次数: 89 全文下载次数: 132
引用本文:

DOI:

10.11834/jrs.20211113

收稿日期:

2021-03-03

修改日期:

2021-06-23

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基于支持向量机的老挝丰沙里省新开辟刀耕火种监测与空间特征分析
摘要:

刀耕火种农业是热带广泛存在且备受争议的传统土地利用类型,在多山且森林覆盖率高的老挝尤甚。人口增长、林业政策与气候变化等正在加剧刀耕火种农业自身演变及其向商品化种植园(如橡胶林)转变。因农林时空转变动态性、相较于现代农业的边缘性及其斑块破碎且分布随机等,热带刀耕火种农业遥感监测历来受到挑战,有关其从业人口、确切分布及其时空动态等问题仍悬而未决。为探究机器学习算法在刀耕火种监测中的应用潜力,利用2016年旱季(4月)两景Landsat OLI 影像,基于支持向量机算法并通过消除建设用地噪声以提高新开辟刀耕火种提取精度(总体精度95%,Kappa系数0.81),据此揭示了老挝丰沙里省新开辟刀耕火种县域差异、与居民点-道路距离以及地形特征。结果表明:(1)当年新开辟刀耕火种约9.88×104hm2(全省占比6%),刀耕火种仍是该省重要土地利用类型,斑块南多北少、西多东少且呈破碎化分布。(2)各县新开辟刀耕火种面积介于1~2万hm2,桑潘县最大(1/5),本讷县最小(1/10)。(3)近九成新开辟刀耕火种集中分布在距居民点5km范围内(山路步行1~2h),且距不同等级道路表现出递减速率不同(次要公路>山路>主要公路)的距离衰减规律,次要公路两侧5km内尤甚。(4)新开辟刀耕火种常见于低山(2/3)斜坡(2/5)地带并以东南坡(2/3)为主,县域变化差异小。

Freshly-opened swidden mapping using support vector machine (SVM) and spatial characteristics analysis in Phongsaly Province, Laos
Abstract:

Swidden agriculture is a widespread but controversial traditional land-use type in the tropics, especially in Laos, which is mountainous and has high forest cover. Due to population growth, forestry policies and climate change, swidden agriculture has been experiencing drastic transformations into commercial plantations (such as rubber). However, the remote sensing monitoring of tropical swidden agriculture has always been challenged. This is partly due to the fact that swidden is a diverse and dynamic land use that is difficult to map and partly because of its marginal feature compared with modern agriculture. There is still very limited information on its exact distribution, temporal and spatial dynamic changes, as well as related population. To explore the application potential of machine learning in monitoring swidden agriculture and understand the spatial characteristics of freshly-opened swidden in Phongsaly Province, Laos, a support machine algorithm (SVM) was improved by combining the information of construction land based on two Landsat OLI images in April, the dry season of 2016. Our results showed that: (1) the extraction accuracy of the SVM for the newly-opened swiddens had been improved with the overall accuracy of 95% and the Kappa coefficient of 0.81. (2) The slash-and-burn cultivation is still a vital land use type in Phongsaly as the newly-opened swidden was about 9.88×104ha (6% of the province) in 2016. More patches were detected in the southwest and fewer in the northeast, with a fragmented distribution. (3) The area of newly-opened swiddens in each district was between 10,000 and 20,000 ha, with Samphanh District ranking the first (1/5) and Boonneua District the last (1/10). (4) Nearly 90% of the newly opened swidden were concentrated within 5km of residential areas (1~2h of walking time), especially 1~4km. The characteristics of the distance from residential areas are relatively consistent at the provincial and district levels. Also, they were mainly distributed in the range of 5km on both sides along minor roads, followed by tracks and major ones. At the district level, the situation conformed to the above regular patterns. (5) The newly-opened swidden mainly distributed in the low mountain area (2/3) with slope gradients of 15~25° (2/5) and aspects of southeast (2/3). The districts of Phongsaly showed similar spatial changes.

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