土壤水分微波反演方法进展和发展趋势

土壤水分是连接地表水循环和能量循环的关键参量,精确获取该参量对于理解气候变化、地表水文过程、地气间能量交换机理等具有重要意义。微波遥感由于其较为合适的探测深度和坚实的理论基础在观测地表浅层土壤水分上具有很大优势,结合反演方法可以获取空间连续的土壤水分含量,有助于更加客观认知土壤水分的时空演变机理。随着微波遥感数据的不断丰富,多种微波遥感土壤水分反演方法相继涌现,为了更好地了解其发展和趋势,本文总结了当前土壤水分微波反演常用的卫星遥感数据并分析其发展趋势,后从主动微波反演、被动微波反演和多源协同反演3个方面梳理了各类土壤水分微波反演方法的原理、发展和优缺点,最终总结出目前微波遥感土壤水分反演方法的发展趋势：即土壤水分微波反演方法的时空普适性逐渐增强、面向高时空分辨率的土壤水分微波协同反演方法快速发展以及土壤水分微波反演方法的智能化水平不断提高。     

EXPERIMENTAL STUDY ON SOIL MOISTURE USING DUAL-FREQUENCY MICROWAVE RADIOMETER

1INTRODUCTIONSoil is the basis of human's living. Soil moisture plays asignificant role in studying the matter and energy ex-changes in global hydrology sphere. The evaporation ofsoil moisture has an influence on the water vapor cycle.Meanwhile soil moisture is also one of the firsthandmeasurable parameters in crop yield estimation and wa-ter resources management (JACKSON et al., 1993). Theinfluence of the interaction of land and atmosphere onsoil moisture can bring about anomalous cli…     

Variation of Thornthwaite moisture index in Hengduan Mountains,China

The Thornthwaite moisture index, an index of the supply of water(precipitation) in an area relative to the climatic demand for water(potential evapotranspiration), was used to examine the spatial and temporal variation of drought and to verify the influence of environmental factors on the drought in the Hengduan Mountains, China. Results indicate that the Thornthwaite moisture index in the Hengduan Mountains had been increasing since 1960 with a rate of 0.1938/yr. Annual Thornthwaite moisture index in Hengduan Mountains was between –97.47 and 67.43 and the spatial heterogeneity was obvious in different seasons. Thornthwaite moisture index was high in the north and low in the south, and the monsoon rainfall had a significant impact on its spatial distribution. The tendency rate of Thornthwaite moisture index variation varied in different seasons, and the increasing trends in spring were greater than that in summer and autumn. However, the Thornthwaite moisture index decreased in winter. Thornthwaite moisture index increased greatly in the north and there was a small growth in the south of Hengduan Mountains. The increase of precipitation and decrease of evaporation lead to the increase of Thornthwaite moisture index. Thornthwaite moisture index has strong correlation with vegetation coverage. It can be seen that the correlation between Normalized Difference Vegetation Index(NDVI) and Thornthwaite moisture index was positive in spring and summer, but negative in autumn and winter. Correlation between Thornthwaite moisture index and relative soil relative moisture content was positive in spring, summer and autumn, but negative in winter. The typical mountainous terrain affect the distribution of temperature, precipitation, wind speed and other meteorological factors in this region, and then affect the spatial distribution of Thornthwaite moisture index. The unique ridge-gorge terrain caused the continuity of water-heat distribution from the north to south, and the water-heat was stronger than that from the east to west part, and thus determined the spatial distribution of Thornthwaite moisture index. The drought in the Hengduan Mountains area is mainly due to the unstable South Asian monsoon rainfall time.     

Deep profile soil moisture distribution characteristics for different microtopographies on the semi-arid Loess Plateau,China

Soil moisture is a limiting factor for vegetation restoration on the Loess Plateau, China. Micro-topography may cause heterogeneities in the distribution of soil moisture, but little is known about its effect on deep soil moisture. Our study aims to explore the distribution and impact of soil moisture within the upper 10 m of soil for different microtopographies. Taking undisturbed slope as the control, five micro-topographies were selected. Soil moisture over a depth of 0-10 m from 2017 to 2019 was investigated, and soil particle size and soil organic matter were measured. Variance analysis and multiple comparisons were used to analyze the difference in soil moisture for different microtopographies and multiple-linear regression was used to analyze the influence of micro-topography on soil moisture. There are significant differences in soil moisture within the different layers underlying the examined micro-topographies, while the inter-annual variation in soil water storage for the selected microtopographies increase with increased rainfall. The depth of influence of micro-topographic vegetation on soil moisture exceeded 1000 cm for a gully(GU), 740 cm for a sink hole(SH), 480 cm for a scarp(SC), 360 cm for an ephemeral gully(EG) and 220 cm for a platform(PL). Micro-topography will cause the heterogeneous distribution of soil moisture in the shallower layers, which changes the vegetation distribution differences between micro-topographies. This may be the survival strategy of herbaceous vegetation in response to climate change in the Loess Plateau. For future vegetation restoration efforts, we need to pay attention to the influence of microtopography on soil moisture.     

东北区域水汽收支的变化及其与降水的关系

为了明确东北区域水汽收支变化及其与降水的关系,利用1970～2010年NCEP/NCAR逐月平均分析资料、国家气象信息中心提供同期的气象站逐日降水实况资料,对东北区域夏半年（5～9月）区域水汽收支的年（年代）际变化及其与降水的关系、降水偏多（少）年的水汽输送特征进行研究.研究结果表明：（1） 1970年代水汽异常输送主要来自华北地区;1980年代,水汽异常输送主要来自蒙古东部和日本海;1990年代,水汽异常输送主要来自鄂霍次克海;2000年以后,水汽异常自东北区域向西南方向输送.总体而言,1970～1990年代区域内的水汽增加,2000年以后区域内水汽明显大幅度减少.（2）东北区域水汽总收支与夏季降水相关性较好,相关系数可达0.79,通过99％的信度检验,南、北边界的水汽输送对该区域的夏季降水有显著影响.（3）东北地区降水偏多年,西北太平洋上的水汽明显增强;降水偏少年,西风带和西北太平洋的水汽输送明显减弱.     

全球36 km格网土壤水分逐日估算

土壤水分是陆面生态系统和能量循环的核心变量之一,利用微波遥感技术获得的土壤水分产品的时间分辨率一般是2-3 d,因此精确地获得具有较高时间分辨率的土壤水分成了人们关注的焦点。本文尝试将SMAP (the Soil Moisture Passive and Active）土壤水分和MODIS光学数据相结合,利用广义回归神经网络进行全球36 km土壤水分的估算,提升SMAP土壤水分的时间分辨率。结果显示,广义回归神经网络估算土壤水分与SMAP保持了高相关性(r = 0.7528),但其却保留了较高的误差 (rmse = 0.0914 m³/m³)。尽管如此,估算的土壤水分能够很好地保持SMAP土壤水分的整体空间变化,并且提升了土壤水分的时间分辨率（1 d）。此处,本文研究了SMAP土壤水分与MODIS光学数据之间的关系,这对今后利用机器学习进行SMAP土壤水分降尺度研究提供了重要的参考价值。     

Advances in Research on Soil Moisture by Microwave Remote Sensing in China

Soil moisture is an important factor in global hydrologic circulation and plays a significant role in the research of hydrology, climatology, and agriculture. Microwave remote sensing is less limited by climate and time, and can measure in large scale. With these characteristics, this technique becomes an effective tool to measure soil moisture. Since the 1980s, Chinese researchers have investigated the soil moisture using microwave instruments. The active re- mote sensors are characteristic of high spatial resolution, thus with launch of a series of satellites, active microwave remote sensing of soil moisture will be emphasized. The passive microwave remote sensing of soil moisture has a long research history, and its retrieval algorithms were developed well, so it is an important tool to retrieve large scale moisture information from satellite data in the future.     

大柳塔采煤塌陷区土壤含水量的空间变异特征分析

通过研究采煤塌陷区土壤水空间分布及动态变化特征,查明了采煤塌陷对土壤含水量的影响,这对矿区生态环境保护、塌陷区土地复垦等具有重要指导意义。以大柳塔双沟采煤塌陷区为试验区,利用传统统计学和地统计学方法分析了采煤塌陷条件下的包气带土壤水空间变异特征。研究结果表明:由于采煤塌陷造成塌陷区土壤层位在垂向上倒置、重组,引起土壤粒度、容重、孔隙度等土壤物理特性的改变,使塌陷区土壤含水量比非塌陷区显著降低,在不同深度层（0~60 cm）分别减少14.2%~21.9%;在垂向分布上塌陷区土壤水分也表现出较强的变异性,其离散系数在不同深度（0~60 cm）与非塌陷区的差值在19.2%~50%之间。根据试验区0 cm、20 cm、40 cm、60 cm四个层面土壤含水量的Kriging插值等值线图显示,土壤含水量低值区均位于塌陷区内的塌陷坑部位,证明地表的地裂缝、塌陷坑、塌陷洞等塌陷形态对土壤持水能力的影响颇为显著。采煤塌陷区土壤含水量降低、空间变异性增强直接导致了地表植被生存环境的恶化,地表景观被严重破坏。     

关于黄土含水量划分的讨论

黄土含水量高低,通常能反映出黄土中含水量的变化规律和土性特点。本文对黄土含水量高低的划分和命名做了初步尝试,并对其划分和命名所考虑的因素和依据做了简要讨论。     

多卫星组合的GPS-MR土壤湿度反演

单天中卫星低高度角状态持续时间较短,导致基于单颗GPS卫星多路径信噪比SNR的土壤湿度反演时间分辨率较低。为保证土壤湿度反演结果的可靠性和准确性,同时改善土壤湿度反演的时间分辨率,顾及信噪比有效高度角区间,提出一种基于多GPS卫星组合的GPS-MR高时间分辨率土壤湿度反演方法。实验结果表明,多卫星延迟相位组合能较好地表征土壤湿度变化趋势,二者相关系数优于0.92;土壤湿度反演时间分辨率由1 d提升为2 h。     

基于BDS三频相位多路径误差的土壤湿度反演

为丰富GNSS-IR技术的数据源,提出一种基于北斗三频载波相位多路径误差的土壤湿度反演方法.实验结果表明,由多路径误差导出的延迟相位与土壤湿度间存在较强的相关性,相关系数为0.97.该方法仅需较少历元的多路径误差便可获得与基于信噪比的GNSS-IR相当的土壤湿度反演精度,更容易实现土壤湿度的高动态监测.     

地表组合粗糙度不确定性引起的SAR反演土壤水分的不确定性分析

地表粗糙度的不确定性是引起SAR土壤水分反演结果不确定性的主要因素,现有研究大多着重于研究单个粗糙度参数（主要是相关长度）的不确定性,直接研究地表组合粗糙度不确定性的较少。本文使用偏度、峰度和四分位距3个指标来量化不确定性,通过在组合粗糙度中加入不同量级高斯噪声进行随机扰动的方法,研究组合粗糙度不确定性在反演过程中的传递,并对反演土壤水分的不确定性进行定量分析。进一步研究反演土壤水分的均方根误差对组合粗糙度不同比例误差范围的响应特征,得到满足反演精度要求的组合粗糙度误差控制范围。样区的实验分析结果表明：组合粗糙度高斯噪声标准差在0-0.045之间时,峰度取值从-0.1984到1.2501,偏度取值从0.0191到0.6791,四分位距取值从0.0018到0.0167,3个量化指标都随组合粗糙度高斯噪声量级的增大而增大,土壤水分反演值有集中在众数附近的趋势,土壤水分低估倾向比高估倾向更明显;本文提出的组合粗糙度误差控制范围可满足反演精度要求,误差控制范围与入射角负相关。     

克里格法的土壤水分遥感尺度转换

 尺度效应往往会制约着定量遥感反演的精度,对地学信息进行空间尺度转换是生产实践的必然要求,而常用的尺度转换模型多利用光谱数据进行差值计算,不适合升尺度和降尺度转换。由于土壤含水量数据具有区域变化量的随机性和结构性特点,本文以15m分辨率的ASTER图像像元为基本单元,采用点克里格法完成ASTER 15m至7.5m分辨率的土壤含水量数据降尺度转换,从分维数的相似程度上来看,转换结果是合理的;并利用块状克里格法对地面实测样点数据进行点到7.5m分辨率的面数据升尺度转换,将升尺度和降尺度转换结果与实测样点均值相比较,结果表明:7.5m分辨率的实测样点土壤水均值误差在1.5782-5.019之间,块状克里格法获取的升尺度土壤含水量数据与点克里格法获取的降尺度土壤含水量数据之间误差则为1.2825-5.0481,可见克里格法考虑了点与周边的关系,所获得的土壤含水量值要优于未考虑空间异质性的土壤含水量平均值。     

Stability analysis of an unsaturated soil slope considering rainfall infiltration based on the Green-Ampt model

Based on the principle of saturated infiltration and the Green-Ampt model, an unsaturated infiltration model for a soil slope surface was established for either constant moisture content, or depth-varying moisture content and the slope. Infiltration parameters in the partially saturated slope were revealed under sustained rainfall. Through analysis of the variation of initial moisture content in the slope, the ponding time, infiltration depth, and infiltration rate were deduced for an unsaturated soil slope subject to rainfall infiltration. There is no ponded water on the surface of the slope under sustained low-intensity rainfall. The results show that the infiltration parameters of an unsaturated slope are influenced by the initial moisture content and the wetting front saturation, the soil cohesion and rainfall intensity under sustained rainfall. More short-term slope failures can occur with the decrease of cohesion of the soil of the slope. The ponding time and infiltration depth differ considering constant or different initial moisture content respectively in the soil slope. Then, best-fit curves of the infiltration rate, ponding time, and infiltration depth to the wetting front saturation were obtained with constant or different initial moisture contents. And the slope failure time is roughly uniform when subject to a rainfall intensity I5 mm/h.     

基于地面三维激光扫描强度数据的潮滩表层含水量估算

大面积潮滩表层含水量的测定是潮滩研究中的难题,传统的测量方法难以同时满足高效和精度的要求。地面三维激光扫描技术凭借其高精度、高分辨率以及主动性强等优点,已经高效运用在潮滩地形研究中。但是,对潮滩含水量进行有效分析,仅利用点云的空间几何信息是不够的,还需要对点云的强度数据进行挖掘。地面激光扫描仪提供了包含目标表面光谱反射特性的点云强度数据,利用强度数据可以有效地进行目标表面特性提取。本文提出了一种新的长距离地面激光扫描仪强度数据改正方法,对入射角和距离效应进行有效改正。利用Riegl VZ-4000长距离地面激光扫描仪建立室内含水量模型并对上海市崇明岛一处潮滩进行测试分析,同时收集26个潮滩沉积物样品并利用传统干湿称重法进行含水量验证计算。结果表明：相比于传统技术,利用改正后的激光强度值估算大面积潮滩沉积物表层含水量是一种精确和高效的方法。改正后的激光强度值与潮滩表层含水量存在幂函数关系,相关系数为0.961,估算精度为91.94%。     

Assimilating ASAR data for estimating soil moisture profile using an ensemble Kalman filter

Active microwave remote sensing data were used to calculate the near-surface soil moisture in the vegetated areas. In this study, Advanced Synthetic Aperture Radar （ASAR） observations of surface soil moisture content were used in a data assimilation framework to improve the estimation of the soil moisture profile at the middle reaches of the Heihe River Basin, Northwest China. A one-dimensional soil moisture assimilation system based on the ensemble Kalman filter （EnKF）, the forward radiative transfer model, crop model, and the Distributed Hydrology-Soil-Vegetation Model （DHSVM） was developed. The crop model, as a semi-empirical model, was used to estimate the surface backscattering of vegetated areas. The DHSVM is a distributed hydrology-vegetation model that explicitly represents the effects of topography and vegetation on water fluxes through the landscape. Numerical experiments were con- ducted to assimilate the ASAR data into the DHSVM and in situ soil moisture at the middle reaches of the Heihe River Basin from June 20 to July 15, 2008. The results indicated that EnKF is effective for assimilating ASAR observations into the hydrological model. Compared with the simulation and in situ observations, the assimilated results were significantly improved in the surface layer and root layer, and the soil moisture varied slightly in the deep layer. Additionally, EnKF is an efficient approach to handle the strongly nonlinear problem which is practical and effective for soil moisture estimation by assimilation of remote sensing data. Moreover, to improve the assimilation results, further studies on obtaining more reliable forcing data and model parameters and increasing the efficiency and accuracy of the remote sensing observations are needed, also improving estimation accuracy of model operator is important.     

秦巴山区植被覆盖与土壤湿度时空变化特征及其相互关系

基于2001-2014年MODIS-NDVI和MODIS-LST数据,利用温度植被干旱指数对土壤湿度进行遥感反演,分析了秦巴山区植被覆盖与土壤湿度时空变化特征及其相互关系。研究发现：① 秦巴山区植被覆盖与土壤湿度均呈增加趋势;② 植被覆盖整体水平较高且表现出“四周低,中间高”的空间分布特征,土壤湿度整体表现出“北低南高”的空间分布特征,大体上二者呈现出空间分布正相关性;③ 植被改善趋势表现明显,显著改善区分布分散,无明显集中区域,退化区域主要集中于北部渭河沿岸及东部边缘少量地区;土壤湿度增长态势明显,增大区分布于除西北边缘及东北边缘外的几乎整个研究区中,减小区域面积小且大部分表现不显著;④ 秦巴山区植被覆盖与土壤湿度时空变化上呈现出明显的正相关性,其中69.71%的区域表现出土壤湿度增大-植被覆盖改善的特征,分布于研究区除四周边缘地带外的大部分地区。     

夏季青藏高原东部地区的水汽输送

本文从分析流场、湿度场的特征入手,对青藏高原东部地区的水汽通量、水汽通量散度进行了计算研究。     

Spatial variability and its main controlling factors of the permafrost soil-moisture on the northern-slope of Bayan Har Mountains in Qinghai-Tibet Plateau

The soil moisture movement is an important carrier of material cycle and energy flow among the various geo-spheres in the cold regions. Thus, this research takes the north slope of Bayan Har Mountains in Qinghai-Tibet Plateau as a case study. The present study firstly investigates the change of permafrost moisture in different slope positions and depths. Based on this investigation, this article attempts to investigate the spatial variability of permafrost moisture and identifies the key influence factors in different terrain conditions. The method of classification and regression tree (CART) is adopted to identify the main controlling factors influencing the soil moisture movement. The relationships between soil moisture and environmental factors are revealed by the use of the method of canonical correspondence analysis (CCA). The results show that: 1) Due to the terrain slope and the freezing-thawing process, the horizontal flow weakens in the freezing period. The vertical migration of the soil moisture movement strengthens. It will lead to that the soil-moisture content in the up-slope is higher than that in the down-slope. The conclusion is contrary during the melting period. 2) Elevation, soil texture, soil temperature and vegetation coverage are the main environmental factors which affect the slope-permafrost soil-moisture. 3) Slope, elevation and vegetation coverage are the main factors that affect the slope-permafrost soil-moisture at the shallow depth of 0-20 cm. It is complex at the middle and lower depth.     

光学信息分解被动微波土壤湿度方法

土壤水分是一个重要生态参量,以被动微波反演土壤水分,不受天气影响,且其算法成熟.但是星载被动微波数据的空间分辨率较低,可适合大区域尺度研究.本文将1km分辨率光学数据MODIS和25km分辨率被动微波数据AMSR- E2级土壤湿度产品结合,利用NDVI-Ts特征空间,去除植被影响,结合前人提出的裸土蒸散模型,将研究区被...