Study on Soil Moisture Content Inversion in an Arid Area Based on Landsat-8 Imagery
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摘要: 土壤水分含量的精确监测对区域生态环境保护与可持续发展具有重要意义。本文以内蒙西部额济纳旗东南的居延泽地区为研究区,基于多期Landsat-8遥感影像和野外实测不同深度的土壤水分含量数据,构建了温度植被干旱指数(TVDI)、垂直干旱指数(PDI)、归一化干旱监测指数(NPDI)和土壤湿度监测指数(SMMI)等四种干旱指数模型,探讨了上述模型在居延泽地区土壤水分含量反演中的精度与适用性,选取精度较优的TVDI模型反演了研究区2015年至2017年的土壤水分含量,并使用随机森林分类法将研究区分为沙地、盐碱地、裸地、植被和滩涂五种地类,探讨了不同地类的土壤水分含量差异。结果表明四种干旱指数均与土壤水分含量实测值呈负相关;从拟合精度看,四种干旱指数均与表层土壤水分含量具有最高的拟合精度,且随着土层深度的增加,拟合精度逐渐变劣。其中TVDI综合表现最优,尤其在表层,R2可达到0.76;研究区不同地类的土壤水分含量存在差异,呈现出从沙地、盐碱地、裸地、植被到滩涂依次升高的规律。Abstract: Accurate estimation of soil moisture content is of great significance for eco-environmental conservation and sustainable development in arid areas. In Juyanze, the southeast of Ejina banner, the western Inner Mongolia, 4 drought index models, including Temperature Vegetation Drought Index (TVDI), Perpendicular Drought Index (PDI), Normalized PDI (NPDI), and Soil Moisture Monitoring Index (SMMI), were established based on 3 Landsat-8 images and 150 in-situ soil moisture samples from different soil depths. Model accuracy and applicability were compared and verified, and the optimal model of TVDI was used to retrieve soil moisture content from 2015 to 2017. Five land use types, namely sandy land, saline-alkali land, bare land, vegetation and tidal flats were classified based on random forest classification and their differences in soil moisture content were analyzed. The results showed that all the 4 drought indices were negatively correlated with the measured soil moisture content. The highest fitting accuracy was observed between the 4 drought indices and the surface soil moisture. Meanwhile, the fitting accuracy decreased with the increase of soil depth. The accuracy of TVDI model was higher than that of the other models, particularly in the surface soil, with a R2 of 0.76. Discrepancies of the average soil moisture content were observed in different land use types, and generally the soil moisture content was the lowest in the sandy land, followed by saline-alkali land, bare land, and vegetation, the highest in the tidal flats.
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Key words:
- Soil moisture content /
- Drought index /
- Landsat-8 /
- Arid area
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表 1 土壤体积含水量分类统计
Table 1. Statistics of soil moisture content
地类Land type 2015年8月28日August 28, 2015 2016年7月29日July 29, 2016 2017年9月2日September 2, 2017 像元比例(%)Pixel ratio 平均土壤水分含量(%)Average soil moisture content 像元比例(%)Pixel ratio 平均土壤水分含量(%)Average soil moisture content 像元比例(%)Pixel ratio 平均土壤水分含量(%)Average soil moisture content 裸地 12.73 4.65 12.33 5.07 12.47 5.57 沙地 63.59 2.13 68.59 2.19 65.69 2.88 盐碱地 18.36 4.10 15.63 4.37 12.53 4.15 滩涂 1.21 31.76 0.52 21.11 2.32 47.70 植被 1.42 9.24 0.61 15.75 2.72 18.33 水体 2.69 — 2.32 — 4.26 — -
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