基于微波遥感反演的黄土高原表层土壤水分变化及其对植被恢复的响应

发布时间：2018-05-16 00:06

本文选题：黄土高原 + 土壤水分　；参考：《西北农林科技大学》2016年博士论文

【摘要】：水分是黄土高原地区生态系统的核心限制因子之一。土壤水分既是土壤的重要组成物质,也是该区旱作农业和植被生长所需水分的直接来源。土壤水分变化及区域差异研究是认识区域气候变化和植被—土壤关系的重要内容,也是科学合理地恢复重建可持续植被的重要基础。黄土高原地区在最近的20年,特别是实行退耕还林(草)工程以来,大规模植被恢复对该区生态环境产生了重要影响,同时也改变了区域地表水土过程和分布特征。为了认识该区表层土壤水分的时空变化特点及其对植被恢复的响应,本研究采用欧洲遥感卫星(ERS)风散射计反演的土壤水分数据和归一化植被指数(NDVI)等遥感资料,依据经典统计学、地统计学,以及时间序列分析理论,从站点和区域两个尺度,结合农田实测土壤水分数据、传统区域调查土壤水分资料,以及土地利用和气候等相关数据,探讨了微波遥感数据反演的土壤水分在黄土高原地区的适用性,确定了适合研究区域的反演模型和参数;采用上述研究结果,结合多断面样带和GIS空间分析方法,调查了黄土高原地区大规模退耕还林(草)工程实施前后表层土壤水分的时空变化特征;进而分析了表层土壤水分与植被恢复重建和降水量的时空耦合关系,初步查清了表层土壤水分变化对大规模植被恢复的相应范围和程度。本研究取得的主要成果如下:(1)通过对欧洲遥感卫星(ERS)风散射计数据与农田气象站实测土壤水分实际观测数据对照分析,结合黄土高原地区土壤特征确定了微波遥感数据表层土壤水分反演模型和参数,计算了黄土高原表层土壤水分数据(土壤湿度指数,SWI)对应的土壤体积含水量(Wswi)。结果表明,遥感反演的土壤体积含水量Wswi和农田实测的表层0~10 cm的土壤水分呈极显著相关,且相关程度随土层深入而逐渐降低,表明该微波遥感反演的数据接近表层土壤水分实际情况,能客观地反映表层土壤水分的分布特征,表现出土壤水分遥感反演数据在黄土高原地区具有良好的适用性,可用于分析表层土壤水分的时间和空间变化分析。(2)研究发现,在农业集中的平原地区,遥感反演的土壤体积含水量Wswi与实测的农田表层土壤水分值相关性较高,而在农业、林业、牧业用地复合交错地区其相关性较差;雨养农业区和灌溉农业区气象站点农田实测的土壤水分和微波遥感反演的土壤水分年内及年际变化趋势均与降水量变化趋势一致,但在相对干旱季节,农田实测水分普遍较卫星反演土壤水分结果高,说明在应用该卫星数据估算农田土壤水分时,除了考虑地貌、土壤、植被、气候等自然因素,同时也应充分考虑农业措施(如灌溉措施)对土壤水分的影响。应用结果表明,现有的反演模型采用的参数主要是依据模型研发地区实际选择的,在应用于其他地区时需依据应用区域的土壤环境特征对反演模型的具体参数加以修正,并依据当地土壤环境观测数据建立适用的反演模型。(3)通过与传统的区域土壤水分调查数据比较,微波遥感反演的0~100 cm表层土壤水分数据较好地反映了1992~2013年黄土高原地区土壤水分的时空变化规律,土壤水分年值总体上表现出南多北少、东高西低的空间分布差异规律。土壤水分季节值较好地反映出土壤水分年内季节动态变化特征:春季失墒、夏季增墒、秋末冬季缓慢失墒。空间上呈现出由东南向西北逐渐减少的特点。不同样带植被、降水和土壤水分分布和变化梯度明显。结果也表明1998~2000年为整个黄土高原植被指数和土壤水分变化的转折点,说明退耕还林(草)工程对黄土高原植被覆盖和土壤水分环境产生了深刻影响。(4)通过分析比较退耕还林(草)工程初期(1998~2000年)和工程开展10年后(2008~2010年)植被恢复重建与表层土壤水分的时空分布特征,发现NDVI显著增加面积占黄土高原总面积的80.99%,而72.64%的地区表层土壤水分呈现减少趋势。植被恢复和土壤水分变化的空间耦合分析表明,黄土高原57.65%的地区植被覆盖增加并且土壤水分减少,而且其中约有32.80%的地区降水量还有所增加;土壤水分和植被覆盖同时增加地区面积约为23.34%;植被覆盖和土壤水分同时减少地区面积占14.99%。研究结果警示人们,在干旱和半干旱的黄土高原地区大规模地植被恢复有可能导致区域性土壤水分条件恶化。必须根据土壤水分变化特征,调整植被建设策略,以达到区域生态恢复的可持续性。
[Abstract]:Soil moisture is one of the key limiting factors of the ecosystem in the Loess Plateau. Soil moisture is not only an important component of soil, but also a direct source of water for drought farming and vegetation growth in this area. The study of soil moisture changes and regional differences is an important content of understanding regional climate change and soil vegetation and soil relations, and is also a science. In the last 20 years, especially since the implementation of the project of returning farmland to forest (grass), the large scale vegetation restoration has had an important impact on the ecological environment of the region, and also changed the regional surface soil and water process and distribution characteristics in the Loess Plateau area. In this study, the remote sensing data of soil moisture data and normalized vegetation index (NDVI) retrieved by the European remote sensing satellite (ERS) wind scatterometer are used in this study. According to the classical statistics, geostatistics, and time series analysis theory, the measured soil water fraction from the site and the area is combined with the two scales of the site and the area. According to the data of soil moisture, land use and climate, the applicability of soil moisture retrieved by microwave remote sensing data in the Loess Plateau area was investigated, and the inversion model and parameters suitable for the study area were determined, and the results were investigated by using the multi section sample zone and the GIS spatial analysis method. The temporal and spatial variation characteristics of soil moisture in the surface soil of the Loess Plateau Region before and after the large-scale reforestation project were carried out, and the spatio-temporal coupling relationship between the surface soil moisture and the vegetation restoration and reconstruction and the precipitation was analyzed, and the corresponding scope and degree of the surface soil moisture change to the large-scale vegetation restoration was preliminarily identified. The results are as follows: (1) the surface soil moisture inversion model and parameters of the microwave remote sensing data are determined by comparing the data of the ERS wind scatterometer with the actual observation data of the measured soil moisture in the farmland weather station, and the soil moisture data of the surface soil of the Loess Plateau (soil moisture) are calculated. The soil volumetric water content (Wswi) corresponding to SWI. The results show that the soil moisture content of the soil volume Wswi retrieved by remote sensing and the soil moisture of the surface 0~10 cm measured by the farmland are very significant, and the correlation degree decreases gradually with the depth of the soil layer, which indicates that the data retrieved by the microwave remote sensing approach is close to the actual condition of the surface soil moisture and can be objective. Reflecting the distribution characteristics of surface soil moisture, it shows that the remote sensing data of soil moisture has good applicability in the Loess Plateau area, and can be used to analyze the time and spatial variation of surface soil moisture. (2) the study found that the volume of soil volume Wswi retrieved by remote sensing and the measured farmland table in the agricultural concentrated plain area The correlation of soil moisture content was relatively high, while in agriculture, forestry, and pastoral land complex interlaced areas, the correlation was poor. The soil moisture and the interannual variation trend of soil moisture and the interannual variation of soil moisture and microwave remote sensing in the rainfed and irrigated agricultural areas were in accordance with the trend of water reduction, but in the relative drought season, The measured soil moisture in farmland is generally higher than that of satellite inversion, which indicates that the effects of agricultural measures (such as irrigation measures) on soil water content should be taken into consideration in the application of the satellite data to the estimation of soil moisture in farmland, and the effects of agricultural measures (such as irrigation measures) on soil water content should be considered. The main parameters are based on the actual selection of the model R & D area. In other areas, the specific parameters of the inversion model need to be modified according to the soil environment characteristics of the applied region, and the applicable inversion model is established according to the local soil environment observation data. (3) by comparing with the traditional regional soil moisture survey data, The 0~100 cm surface soil moisture data retrieved by wave remote sensing can better reflect the temporal and spatial variation of soil moisture in the Loess Plateau Region in 1992~2013, and the annual value of soil moisture shows the difference of spatial distribution in the South and the East, and the seasonal value of soil moisture is a good reflection of the seasonal dynamic changes of soil moisture. In spring, soil moisture loss, summer soil moisture increase, and slow loss of soil moisture in the end of autumn. There is a gradual decrease in space from southeast to northwest. It is not the same with vegetation, precipitation and soil moisture distribution and change gradient. The result also indicates that 1998~2000 year is the turning point of the whole Loess Plateau vegetation index and soil moisture change, indicating the return of farmland to forest (grass). The project has a profound influence on the vegetation cover and soil water environment in the Loess Plateau. (4) by analyzing and comparing the spatial and temporal distribution characteristics of the vegetation restoration and reconstruction and the surface soil moisture in the early period of the project (1998~2000 years) and the 10 years of the project, it was found that the significant increase in the area of NDVI accounted for 80.99% of the total area of the Loess Plateau. The spatial coupling analysis of vegetation recovery and soil water change showed that vegetation coverage increased and soil moisture decreased in 57.65% of the Loess Plateau, and about 32.80% of the areas had increased rainfall and increased soil moisture and vegetation coverage at the same time in 72.64% of the region. For 23.34%, the results of 14.99%. study on vegetation coverage and soil moisture reduction are a warning that large-scale vegetation recovery in arid and semi-arid loess plateau areas may cause regional soil water conditions to deteriorate. The vegetation construction strategy must be adjusted to achieve regional ecological restoration according to the characteristics of soil moisture change. The sustainability of the complex.

【学位授予单位】：西北农林科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：S152.7;Q948

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