基于机载极化雷达技术的农作物覆盖区土壤水分估算

从研究区辅助数据中获得植被覆盖区域农作物含水量，并对“水云模型”的参数进行了修改。从总的极化雷达后向散射中去除了植被影响；再应用简化的裸露地表模型和多极化数据特征消除了地表粗糙度的影响，从而能够通过多极化雷达数据得到地表土壤水分。经过文测数据验证表明农作物覆盖地表土壤水分变化的估算算法还需要更进一步发展和改进以提高反演精度，并探讨了应用极化雷达技术估算植被覆盖区土壤水分的方法。     

基于MODIS数据新疆土壤干旱特征分析

干旱是一种常见的自然灾害,严重影响着新疆的农业生产。利用中分辨率成像光谱仪MODIS影像MOD11A2数据和MOD13A2数据,数字高程模型(DEM)对Ts进行了纠正,提取归一化植被指数(NDVI)和地表温度(Ts)构建NDVI-Ts特征空间,并依据特征空间计算的温度植被干旱指数(TVDI)作为监测土壤湿度指标,反演了新疆2013年5、6、7三个月每16 d的土壤湿度。较好地反映地表图层土壤湿度,分析了新疆土壤湿度的时空分布特征,新疆北部地区土壤湿度高于南部,西部的土壤湿度高于东部,且土壤湿度由西北向东南逐步减小,依次表现为湿润>正常>轻旱>中旱>重旱>极旱;由5月到7月土壤湿度不断增大,这与新疆降水量分布和实地土壤含水率十分吻合,监测结果可信,能够为决策部门防旱抗旱提供有力的信息支持。     

基于ASAR双极化雷达数据的半经验模型反演土壤湿度

基于ENVISAT ASAR-APP数据,利用AIEM(改进积分方程模型)模拟分析粗糙度、土壤水分对ASAR 7个入射角后向散射系数的影响.建立小人射角模式ASAR数据后向散射模型和组合粗糙度计算模型,提出小入射角模式下双极化ASAR数据土壤水分反演半经验模型.基于A1EM模拟数据进行试验,验证了该模型的合理性,且反演的土壤水分和实测土壤水分相关系数为O.92,均方根误差(RMSE)为3.98%.     

基于卫星遥感和再分析数据的青藏高原土壤湿度数据评估

土壤水是地表与大气在水热交换方面的关键纽带,是关键水循环要素,更是地表产汇流过程的关键控制因子。青藏高原是地球第三极,也是亚洲水塔,探讨青藏高原土壤水变化对于探讨青藏高原热力学特征变化及其对东亚乃至全球气候变化的影响具有重要意义,而获取高精度长序列大尺度土壤水数据集则是其关键。本文利用青藏高原100个土壤水站点观测数据,从多空间尺度（0.25°×0.25°,0.5°×0.5°,1°×1°）、多时间段（冻结和融化期）等角度,采用多评价指标（R、RMSE、Bias）,对多套遥感反演和同化数据（ECV、ERA-Interim、MERRA、Noah）进行全面评估。结果表明：① 除ERA外,其他数据均能反映青藏高原土壤水变化,且与降水量变化一致。而在那曲地区,遥感反演和同化数据均明显低估实测土壤水含量。从空间分布来看,MERRA和Noah与植被指数最为一致,可很好地反映土壤水空间变化特征;② 青藏高原大部分地区土壤水变化主要受降水影响,其中青藏高原西部边缘与喜马拉雅地区土壤水变化则受冰雪融水和降水的共同影响;③ 除阿里地区外,大部分遥感反演和同化数据在融化期与实测土壤水相关性高于冻结期,其中在那曲地区,遥感反演和同化数据均高估冻结期土壤含水量,却低估融化期土壤含水量。另外,遥感反演和同化数据对中大空间尺度土壤水的估计要好于对小空间尺度土壤水的估计。本研究为青藏高原土壤水研究的数据集选择提供重要理论依据。     

Spatial Variability and Persistence of Soil Moisture in Oklahoma

Using a hydrologic model to estimate daily soil moisture at 258 evaluation locations over a 30-year period, the spatial variability and persistence of soil moisture across Oklahoma is examined. The Soil and Water Assessment Tool (SWAT) uses readily available meteorological inputs with detailed land surface information. Spatial variability of soil moisture across Oklahoma is extremely dynamic and exhibits a remarkable range of individual characteristics due to the heterogeneous land surface. An autocorrelation analysis is used to evaluate the persistence of soil moisture at each evaluation location. In general, soil moisture across Oklahoma persists from 5 to 10 weeks in the eastern portion of Oklahoma to over 30 weeks in western Oklahoma as a result of the large-scale climatic variability of precipitation supply and evapotranspiration demand. However, the lags are not spatially coherent due to the heterogeneity of the land surface. Land surface characteristics potentially influencing the persistence of soil moisture across Oklahoma are examined, including vegetation type and soil texture and depth. Of the three parameters, soil depth plays a significant role in the memory of soil moisture conditions. As the soil profile depth increases, a corresponding increase in the persistence of soil moisture occurs.     

河北坝上土地利用方式对农田土壤风蚀的影响

采用集沙仪、风速廓线仪和土壤紧实度仪对河北坝上地区多种土地利用方式的风蚀因子和输沙量进行观测。结果表明：土壤含水率与输沙量相关性最大,是影响风蚀量的关键性因子。回归拟合显示,风蚀因子与输沙量均符合三次函数方程。在各土地利用方式中,退耕地的地表粗糙度、土壤含水率和土壤硬度最大,其次为东西向莜麦留茬地、小麦留茬地、南北向莜麦留茬地,再次为油菜留茬地和弃耕地,最小为翻耕地。输沙量退耕地最小,其次为东西向莜麦留茬地、南北向莜麦留茬地、小麦留茬地,再次为油菜留茬地和弃耕地,最大为翻耕地;输沙量垂向分布随集沙高度增加呈幂函数减少。因此,适宜增加退耕地和留茬地的分布面积,减少翻耕地面积和垄向沿盛行风向分布的地块有利于降低农田土壤风蚀程度。     

东北黑土区土壤剖面地温和水分变化规律

东北黑土区土壤侵蚀的结果使土壤在坡面上发生再分配,土壤腐殖质层厚度的空间变异增大。腐殖质层厚度的变化又引起地温和土壤水分等土壤物理性质的变化,地温和水分是影响和反映冻融侵蚀作用的重要因子,也是影响地表和土壤剖面物质运移的重要因素。本文通过实测不同厚度腐殖质层剖面的地温和土壤水分,分析了地温和水分随时间和土壤剖面深度的变化规律。结果显示腐殖质层厚度对土壤温度和含水量有显著影响,腐殖质层较厚的剖面解冻速度比薄层黑土区要慢,不同深度土层温度到达0℃的日期也不相同,腐殖质层较厚的剖面冻结时间要滞后1周左右。同时,腐殖质层较厚的黑土区土壤含水量明显大于薄层黑土区,土壤水分运移的深度范围也大。     

Changes in intensity of wind erosion at different stages of degradation development in grasslands of Inner Mongolia, China

Overgrazing by increasing numbers of livestock in the Horqin Sandy Land of Inner Mongolia, China, has led to extensive degradation of the region's sandy steppes. Degraded grasslands are generally classified into four main types: fixed (least degradation), semi-fixed (light degradation), semi-shifting (moderate degradation) and shifting (severe degradation) sandy lands, representing four stages of degradation development. An experiment was conducted in the Horqin Sandy Land to investigate changes in intensity of wind erosion at different stages of degradation development in sandy grasslands and determine the extent to which surface wind erosion was affected by surface-related soil and vegetation factors through their effects on surface roughness length and wind regimes. Daily wind erosion rate was monitored at four sites of degraded grassland over an erosive period from 1 April to 10 June in 2001. Soil and vegetation properties for these sites were also measured twice: one in mid-April prior to the establishment of vegetation and again in mid-June after the establishment of vegetation. Relationships between surface roughness length and soil and vegetation variables were examined at each of the two stages of vegetation development. This study shows striking differences in the intensity of surface wind erosion among sites. The daily wind erosion rate in the fixed sandy land was, on average, only about 1/5 of the rate in the semi-fixed sandy land, 1/14 of the rate in the semi-shifting sandy land and 1/47 of the rate in the shifting sandy land suggesting a much higher resistance of the fixed sandy land to wind erosion compared to other sites. Differences in rate of wind erosion between sites were attributed to between-site differences in soil and vegetation properties that exerted significant effects on wind regimes by altering surface roughness length. At the pre-establishment stage of vegetation, surface roughness length was determined by a combination of litter amount on the ground, soil surface hardness and soil moisture content, with litter amount explaining the greatest proportion of the variation. At the post-establishment stage of vegetation, the development of the surface roughness effects was mainly governed by vegetation characteristics (vegetation cover in particular), while the effects of soil surface hardness and soil moisture on surface roughness length are likely to be masked by vegetation effects. The findings suggest that better management practices of restoring vegetation in degraded grasslands are required to reduce soil erosion losses and achieve a sustainable livestock production in the Horqin Sandy Land, an ecologically fragile sandy land ecosystem.     

大柴旦盐湖采卤区地层剖面盐渍土基本类型及其抗剪强度试验研究

选取柴达木盆地大柴旦盐湖采卤区作为试验区,对区内地层剖面盐渍土的基本类型进行划分,即通过测定Na+、Mg2+、Cl-等易溶盐离子的方法,得出区内采卤区地层剖面盐渍土的主要类型是以亚氯盐渍土为主。在此基础上,对盐渍土进行扰动试样的室内直剪试验研究,以获取抗剪强度指标粘聚力c值与内摩擦角φ值。试验结果表明,该区盐渍土的含盐量由地表开始向下呈逐渐降低趋势,即由地表的6.89%降到地下4.5 m处的1.11%。粘聚力c值主要受试样含水量大小的影响,表现出随着含水量的增加,粘聚力c值呈降低现象,即当含水量由19.8%上升至23.3%时,粘聚力c值由35.4 k Pa下降至24.9 k Pa,下降率约为29.7%;而当含水量由23.3%下降至17.4%时,粘聚力c值则由24.9 k Pa上升至34.1 k Pa,上升率约为36.9%。内摩擦角φ值则受试样粒径影响相对较为明显,随着试样中粘粒含量的增多,粗粒含量相对减少,内摩擦角呈逐渐增大的趋势,即由24.1°上升至33.3°,增加率约为37.3%。随着试样中含盐量的增加,粘聚力c值和内摩擦角φ值均呈线性增加趋势。该研究成果将有助于进一步探讨含水量、颗粒大小以及含盐量对盐渍土试样抗剪强度变化的影响,且对区内盐田及其相应的基础设施建设有一定的理论指导意义。     

荒漠地区地表反照率与土壤湿度相关性研究

本试验分别对腾格里沙漠东南缘沙坡头地区流动沙丘和1964年建植的人工固沙植被区生物土壤结皮的地表反照率和土壤湿度进行了同步测定。分析了该区这两种地表类型的反照率与太阳高度角和土壤湿度的相关性,分别提出了地表反照率与太阳高度角和土壤表层(0～2 cm)湿度的经验拟合关系式。结果表明,地表反照率随太阳高度角增加呈指数递减;排除太阳高度角的影响后,地表反照率随土壤湿度的增加也呈指数递减关系;流沙地表反照率对土壤湿度变化的响应要比生物土壤结皮地表敏感。     

黄土丘陵沟壑区不同深度土壤水分对降雨的响应及其稳定性

通过采用点面结合的方法,分析黄土高原地区降雨影响下不同深度土壤水分的时空变化,从土壤水分复杂的“变异性”中提取相对的“不变性”。结果表明:20 cm以上土壤水分无明显规律,难以表征不同植被类型或空间位置上的土壤水分差异;小于30 mm的降雨基本不会引起40 cm以下土壤水分明显波动;100 cm深处,各采样点的土壤水分能在一个稳定值上保持数月时间,在大于46 mm的强降雨之后出现阶梯式抬升,之后又保持稳定状态;越往土层深处,土壤水分时空稳定性越明显,能较好的表征各植被类型或空间位置上的土壤水分差异。该研究从土壤水分的稳定性角度进行分析,对黄土高原土壤水分的地面采样设计和时空预测具有实际应用价值。     

基于TVDI的黄土高原地表干燥度与土地利用的关系研究

基于地表温度和植被指数的经验关系构建地表干燥度指数。该指数对Ts/NDVI特征空间的生态特征的解释,对土壤和作物的水分含量具有一定的指示意义。通过对地表干燥度进行分级,分析陕北黄土高原区地表含水状况的空间差异,进而结合该地区的主要土地利用类型,探讨各类型的干燥度情况,并对不同地表干燥度条件下各土地利用类型对地表水分的保持能力差异进行分析,结果表明,在该区相对湿润环境中,林地以及疏林地的水分保持能力优于农地和草地,但在干旱的环境下,草地则好于林地及疏林地。建议根据不同土地利用类型的保水能力,在湿润区域增加林地的面积比例,在偏湿润区域增加疏林地的面积,在干旱区域增加草地的比例,减少农地开垦。     

Assessing artificial neural networks coupled with wavelet analysis for multi-layer soil moisture dynamics prediction

Soil moisture simulation and prediction in semi-arid regions are important for agricultural production,soil conservation and climate change.However,considerable heterogeneity in the spatial distribution of soil moisture,and poor ability of distributed hydrological models to estimate it,severely impact the use of soil moisture models in research and practical applications.In this study,a newly-developed technique of coupled(WA-ANN) wavelet analysis(WA) and artificial neural network(ANN) was applied for a multi-layer soil moisture simulation in the Pailugou catchment of the Qilian Mountains,Gansu Province, China.Datasets included seven meteorological factors:air and land surface temperatures,relative humidity,global radiation, atmospheric pressure,wind speed,precipitation,and soil water content at 20,40,60,80,120 and 160 cm.To investigate the effectiveness of WA-ANN,ANN was applied by itself to conduct a comparison.Three main findings of this study were:(1) ANN and WA-ANN provided a statistically reliable and robust prediction of soil moisture in both the root zone and deepest soil layer studied(NSE >0.85,NSE means Nash-Sutcliffe Efficiency coefficient);(2) when input meteorological factors were transformed using maximum signal to noise ratio(SNR) and one-dimensional auto de-noising algorithm(heursure) in WA, the coupling technique improved the performance of ANN especially for soil moisture at 160 cm depth;(3) the results of multi-layer soil moisture prediction indicated that there may be different sources of water at different soil layers,and this can be used as an indicator of the maximum impact depth of meteorological factors on the soil water content at this study site.We conclude that our results show that appropriate simulation methodology can provide optimal simulation with a minimum distortion of the raw-time series;the new method used here is applicable to soil sciences and management applications.     

气候变化对太行山土壤水分及植被的影响

在太行山低山区将自然植被移入蒸渗仪,观察当降水分别为常年平均降水量的80%、90%、100%、110%和120%等5种处理条件下,植被生产力和土壤的不同反映。研究发现:受验植被对降水反映敏感,降水每增加10%,植被生产力增加15%左右,预示未来全球变化导致的降水变化会对太行山低山区植被产生影响。同时在利用野外实验结果对WAVES模型进行验证的基础上,模拟了不同温度和降水变化情景下,土壤水分的可能变化趋势。结果表明:增温和减少降水对土壤水分负作用明显,尽管降水增加可改善土壤的水分供应状况,但降水增加10%对土壤水分的正面影响,大体被3 oC的增温抵消。由于模型模拟中采用的是与目前没有改变降水条件的实验相同的植被(LAI),而植被生长在太行山这一半湿润、半干旱地区又受土壤水分控制,因而估计未来气候变化情景下的植被变化与土壤水分的变化趋势相似。     

灌溉方式对现代绿洲影响的数值模拟

灌溉是农业发展的根本,没有灌溉就没有荒漠区农业。利用美国NCAR中尺度模式MM5V3模拟了喷灌与不同水量地灌以及没有灌溉对绿洲土壤湿度、地下径流以及感热、潜热通量的不同影响。结果表明:①地灌后地表蒸发与植被层的蒸腾更旺盛,散失的水分更多;而喷灌可以抑制地表蒸发与植被层的蒸腾,对土壤水的保持更有利。②喷灌试验要在土壤湿度达饱和以后才会形成地下径流量,而地灌试验则是土壤湿度与地下径流量同时增长。总之,喷灌方式是一种高效节水的灌溉方式,它比其它灌溉方法更有利于绿洲农业生态系统的温度整体降低,不论土壤湿度还是大气湿度都会相应增大,抑制地表土壤水分的蒸发,有利于绿洲农业维持。     

邻近绿洲的荒漠表层土壤逆湿和对水分"呼吸"过程的分析

利用"我国西北干旱区陆气相互作用试验"2000年8~9月在甘肃敦煌进行的野外观测资料,分析了临近绿洲的荒漠戈壁土壤湿度和大气湿度特征,发现:活动层内土壤空气湿度远离饱和状态,水分以气态和液态两种形态存在和输送;由于绿洲效应影响,临近绿洲的荒漠戈壁不仅近地层空气多为逆湿,而且这种空气逆湿在夜间较强时可以继续向土壤活动层延伸。土壤湿度日变化能清楚地被区分为湿维持(1~6时)、水分损失(7~11时)、干维持(12~18时)和水分补充(19~0时)等4个阶段,其中湿维持阶段的土壤逆湿是最主要的结构特征,这一土壤湿度结构表明夜间土壤可以通过凝结吸收大气水分,它与白天的土壤水分蒸发共同构成土壤对大气水分的"呼吸"过程;活动层土壤逆湿的形成与土壤温度状态、大气逆湿强度和大气稳定度都有关。     

咸阳市三原县新庄不同植被土层含水量研究

通过测定咸阳市三原县新庄2005和2006年降雨正常年份人工林地土壤含水量得知,从地表向下土层含水量呈由高到低再到高的变化;2005年草地和玉米地土层含水量由上向下呈逐渐增高趋势,比同年12龄杨树林地和13龄中国梧桐林地平均含水量高约7%。2003年降水量达880 mm丰水年后,人工林土壤干层中水分完全恢复,人工林出现持续近4年茂盛生长期,预计2007年该区将会再次出现发育弱的土壤干层。     

Impacts of snow cover and frozen soil in the Tibetan Plateau on summer precipitation in China

This paper presents an analysis of the mechanisms and impacts of snow cover and frozen soil in the Tibetan Plateau on the summer precipitation in China, using RegCM3 version 3.1 model simulations. Comparisons of simulations vs. observations show that RegCM3 well captures these impacts. Results indicate that in a more-snow year with deep frozen soil there will be more precipitation in the Yangtze River Basin and central Northwest China, western Inner Mongolia, and Xinjiang, but less precipitation in Northeast China, North China, South China, and most of Southwest China. In a less-snow year with deep frozen soil, however, there will be more precipitation in Northeast China, North China, and southern South China, but less precipitation in the Yangtze River Basin and in northern South China. Such differences may be attributed to different combination patterns of melting snow and thawing frozen soil on the Plateau, which may change soil moisture as well as cause differences in energy absorption in the phase change processes of snow cover and frozen soil. These factors may produce more surface sensible heat in more-snow years when the frozen soil is deep than when the frozen soil is shallow. The higher surface sensible heat may lead to a stronger updraft over the Plateau, eventually contributing to a stronger South Asia High and West Pacific Subtropical High. Due to different values of the wind fields at 850 hPa, a convergence zone will form over the Yangtze River Basin, which may produce more summer precipitation in the basin area but less precipitation in North China and South China. However, because soil moisture depends on ice content, in less-snow years with deep frozen soil, the soil moisture will be higher. The combination of higher frozen soil moisture with latent heat absorption in the phase change process may generate less surface sensible heat and consequently a weaker updraft motion over the Plateau. As a result, both the South Asia High and the West Pacific Subtropical High will be weaker, hence causing more summer precipitation in northern China but less in southern China.     

青藏高原地表土壤水变化、影响因子及未来预估

土壤水分是地表和大气连接的纽带,在水文循环中扮演着重要角色。青藏高原作为“第三极”和“亚洲水塔”,其土壤水分对周边地区的气候如亚洲季风的形成和维持产生重要影响,也深刻影响着亚洲水资源的可利用量。基于分布在青藏高原3个气候区的100个站点的实测土壤水数据,对ECV、ERA、MERRA、Noah数据集进行评价,选择对土壤水分评估效果最好的数据集,分析各种气象要素对土壤水分时空格局的影响,并预估未来100年内青藏高原土壤水变化,探讨可能气候成因。结果表明：① Noah数据集对青藏高原历史时期土壤水分评估效果最好,相对其他地区,各数据集对那曲地区土壤水分评估效果最优;② 在各种气象因子中,降水是影响大部分地区土壤水分时空变化的最主要因子,但在喜马拉雅山脉地带,尤其山脉北坡,温度和太阳辐射有较高的影响;③ 1948-1970年土壤水分有明显的下降趋势,1970-1990年土壤水分呈波动变化,无明显趋势,1990-2005年土壤水分有一定的上升趋势,2005年后至今土壤水分有明显快速下降趋势：④ 不同未来情景,土壤水分有下降趋势,其中在CRP 8.5情景下,土壤水分下降最为明显,在2080年之后有更加显著的下降趋势;⑤ 未来降水和温度均呈上升趋势,其中干旱指数变化在RCP 8.5情景下呈下降趋势,在RCP 2.6和RCP 4.5情景下无明显变化,干旱指数在一定程度上能解释未来土壤水分的变化格局。     

下垫面因素对喀斯特地区水分利用效率的影响

水分利用效率是衡量陆地生态系统对气候变化响应的重要指标,而下垫面因素通过影响局部气候进而影响水分利用效率。喀斯特地区生态缺水严重且下垫面情况复杂,但目前该区域多个下垫面因素对水分利用效率的综合影响仍不明晰。论文利用MODIS GPP和ET数据集计算中国西南喀斯特地区的水分利用效率,结合岩性组合、土壤类型、土地利用类型及地表粗糙度,采用广义线性模型,揭示了下垫面因素对水分利用效率的综合影响。结果表明：研究区水分利用效率受海拔和喀斯特发育程度综合影响,在空间上从东南向西北逐渐升高。下垫面因素中岩性组合对水分利用效率的影响表现出了喀斯特与非喀斯特地区的差异,喀斯特地区的碳酸盐岩岩性组合对水分利用效率呈负向影响,纯喀斯特岩性组合比非纯喀斯特岩性组合负向影响更强;土壤类型对水分利用效率的影响受分布海拔高度差异、土壤有机质差异及喀斯特与非喀斯特地貌差异3种因素影响;土地利用类型总体上呈植被越茂盛的地类对水分利用效率的正向影响越强的趋势;地表粗糙度的增大先对水分利用效率趋正向影响,后趋于负向影响。碳酸盐岩影响土壤性质,而土壤性质和地表粗糙度共同影响植被来对喀斯特地区的水分利用效率产生综合影响。