Coupling numerical simulation with remotely sensed information for the study of frozen soil dynamics

The acquisition of spatial-temporal information of frozen soil is fundamental for the study of frozen soil dynamics and its feedback to climate change in cold regions. With advancement of remote sensing and better understanding of frozen soil dynamics, discrimination of freeze and thaw status of surface soil based on passive microwave remote sensing and numerical simulation of frozen soil processes under water and heat transfer principles provides valuable means for regional and global frozen soil dynamic monitoring and systematic spatial-temporal responses to global change. However, as an important data source of frozen soil processes, remotely sensed information has not yet been fully utilized in the numerical simulation of frozen soil processes. Although great progress has been made in remote sensing and frozen soil physics, yet few frozen soil research has been done on the application of remotely sensed information in association with the numerical model for frozen soil process studies. In the present study, a distributed numerical model for frozen soil dynamic studies based on coupled water-heat transferring theory in association with remotely sensed frozen soil datasets was developed. In order to reduce the uncertainty of the simulation, the remotely sensed frozen soil information was used to monitor and modify relevant parameters in the process of model simulation. The remotely sensed information and numerically simulated spatial-temporal frozen soil processes were validated by in-situ field observations in cold regions near the town of Naqu on the East-Central Tibetan Plateau. The results suggest that the overall accuracy of the algorithm for discriminating freeze and thaw status of surface soil based on passive microwave remote sensing was more than 95%. These results provided an accurate initial freeze and thaw status of surface soil for coupling and calibrating the numerical model of this study. The numerically simulated frozen soil processes demonstrated good performance of the distributed numerical model based on the coupled water-heat transferring theory. The relatively larger uncertainties of the numerical model were found in alternating periods between freezing and thawing of surface soil. The average accuracy increased by about 5% after integrating remotely sensed information on the surface soil. The simulation accuracy was significantly improved, especially in transition periods between freezing and thawing of the surface soil.     

塔里木河中游典型绿洲盐渍化土壤的反射光谱特征

研究盐渍化土壤的光谱特性是利用遥感技术实现在区域尺度上进行土壤盐渍化监测和评价的工作基础, 是建立地面数据和遥感数据关系的桥梁。本文以塔里木河中游典型绿洲--渭干河-库车河三角洲绿洲为研究对象, 采用光谱学技术以及多元统计相结合的方法, 研究干旱区典型绿洲盐渍化土壤的反射光谱特征。首先, 对光谱数据进行预处理(去噪、剔除水分吸收波段), 以便消除仪器本身噪声及外界条件的影响, 并且计算了部分盐渍地样本的光谱吸收特征参数, 说明相同程度的盐渍化土壤具有相似的吸收特征;其次, 研究盐渍化土壤的反射光谱与盐分因子(八大离子、电导率(EC)、含盐量(salt content)、pH、总溶解固体(TDS)等) 之间的关系, 并选择具有代表性的盐分因子与野外实测光谱数据建立定量回归模型, 通过多元线性回归分析得出含盐量、SO₄^2-、TDS、EC与原始光谱数据的相关性分别是0.746、0.908、0.798 和0.933, 达到了理想的效果。本研究对于干旱区典型绿洲盐渍土的光谱特征研究有着重要指示意义, 为发展和完善中国盐渍土理化特征的可见光-近红外反射光谱分析理论奠定科学积累, 并进一步为干旱区土壤盐渍化、沙漠化灾害等环境恶化问题的解决提供新的科学技术手段。     

1960-2015年新疆塔什库尔干河谷季节性冻土对气候变化的响应

利用1960-2015 年新疆塔什库尔干河谷季节性冻土的冻结始日、冻结终日、年冻结日数、年累积冻土厚度、最大冻土深度等特征指标资料,采用气候倾向率、气候突变、气候变化趋势的持续性等方法,分析近56 a该地区季节性冻土的年际、年代际变化特征。研究发现：（1）在全球变暖的背景下,1960-2015 年新疆塔什库尔干河谷气温变化亦呈上升趋势,升温趋势的持续性较强,升温幅度0.03 ℃·a^-1、0.29 ℃·（10 a）^-1、0.74 ℃·（30 a）^-1。（2）在1960-2015年期间,该地区季节性冻土呈退化趋势,具体表现为;冻结始日推迟,冻结终日提前,年冻结日数减少,年累积冻土厚度减小,最大冻土深度减小。（3）在1960-2015年期间,该地区季节性冻土持续退化趋势持续性强。（4）1960-2015 年新疆塔什库尔干河谷季节性冻土对气温变暖的具体响应呈现为退化状态。（5）按气候升温率Gt;0.034~0.046 ℃·a^-1 计算,在气候变暖背景下,该地区季节性冻土到2050 年（较2000 年）的冻结始日将推迟12~15 d、年冻结日数将减少21~27 d、年累积冻土厚度将减少36.3%~46.7%。     

不同土壤侵蚀背景下土地利用的时空演变

为了研究土地利用、土地覆盖的时空变化，本文在遥感技术与GIS技术的支持下，对不同土壤侵蚀背景下土地利用的时间动态特征和空间动态特征进行了定量分析。具体表现为通过空间分析，对中国近五年来不同土壤侵蚀背景下的土地利用类型，如耕地状况、森林植被覆盖、城镇工矿建设用地等时空特征进行了动态分析。研究结果表明：我国土壤侵蚀以水力、风力、冻融侵蚀为主，水力侵蚀以微度水力侵蚀为主，在微度水力侵蚀区，耕地、草地、建设用地面积增加，其中耕地增加最多，林地、未利用地面积逐渐减少。风力侵蚀以剧烈风力侵蚀为主，在微度风力侵蚀区，草地面积减少，而未利用地的面积增加；在轻度、中度、强度风力侵蚀区，耕地、林地、未利用地用地面积增加，草地面积减少。在冻融侵蚀区，草地面积有显著增加，而未利用地面积减小。     

Numerical simulations on cutting of frozen soil using HJC Model

Numerical simulation is known as an effective method for mechanical properties during frozen soil excavation. In order to reveal the development of cutting force, effective stress and cutting fragments in frozen silt during the cutting process, we introduce an explicit finite element program LS-DYNA to establish a two-dimensional numerical model of the frozen soil cut. We also use the Holmquist-Johnson-Cook(HJC) damage constitutive model for simulating the variation of soil mechanical properties according to the strong dependence between the cutting tool and frozen silt during the process with different cutting depths, angles and velocities. Meanwhile, a series of experimental results are acquired of frozen silt cutting to prove the application of the HJC model during simulation of cutting force variations. The result shows that the cutting force and fragment size are strongly influenced by cutting depths and cutting velocities increased, and the maximum effective stress at points where the tool contacts frozen soil during the cutting process. In addition, when the cutting angle is 52°, the cutting force is the smallest, and the cutting angle is optimum. Thus, the prediction of frozen soil mechanical properties on the cutting process by this model is conducive to selecting machinery equipment in the field.     

1981—2018年内蒙古典型草原季节性冻土对气候变化的响应

以1981—2018年内蒙古典型草原季节性冻土为研究对象,通过气候倾向率、Mann-Kendall法、多元线性回归等方法,分析最大冻土时空分布特征、年际、年代际变化,研究影响最大冻土深度变化的气象因子。结果表明：（1） 内蒙古典型草原季节性冻土冻结初日在9—11月,终日在4—6月,年内最大冻土深度出现在2—3月,深度在100~280 cm之间。（2） 最大冻土深度年际变化分为下开口抛物线型、上开口抛物线型、正弦曲线型,从最大冻土深度气候倾向率看呈现减小趋势的站点有68%。（3） 最大冻土深度年代际变化分为逐年代递减、减-增型和无明显变化规律,50%的站点在1989年以后最大冻土深度发生突变。（4） 多元线性回归表明气温冻结指数、年平均风速、年极端最低气温对最大冻土深度产生显著影响。该研究揭示了最大冻土深度存在退化的事实,为草原应对气候变化提供指导,为陆地土壤和大气碳循环交换的研究给出提示。     

贡嘎山高山生态系统观测试验和研究进展

贡嘎山高山生态系统观测试验站于1987年正式建站。近20 a来,开展了水、土、气、生等多方面的长期监测与试验,并以环境变化下的亚高山森林生态研究为主线,以生态过程和水文过程为核心,对贡嘎山及其邻近地区的现代自然生态环境特征、森林生态系统结构与功能、冰冻圈演化与动态和第四纪以来的环境演变等展开了多学科研究,为推动我国山地科学和森林生态研究发展做出了重要贡献。在对近20 a来贡嘎山站的研究成果进行总结的基础上,提出了今后应重点加强研究的领域。     

Vibration characteristics of frozen soil under moving track loads

Vibration due to moving traffic loads is an important factor which induces frozen soil damage; this paper analyzed these vibration characteristics of frozen soil foundation under track loads. Firstly, seismic observation array(SOA) technology was applied to monitor the three dimensional dynamic characteristics of frozen soil under movable track load in a permafrost region and seasonal frozen soil area. Secondly, a numerical simulation for the response of frozen soil under movable track load was performed based on finite element analysis(FEA). The results show that dynamic characteristics of frozen soil in perpendicular and parallel direction of the track are obviously different. In the direction perpendicular to the track, the vertical acceleration amplitude had an abrupt increase in the 9–10 m from the track line. In the direction parallel to the track, the acceleration in vertical and horizontal direction had a quick attenuation compared to the other direction. Lastly, various parameters were analyzed for the purpose of controlling the dynamic response of frozen soil and the vibration attenuation in frozen soil layer.     

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.     

基于MODIS温度的青藏高原多年冻土活动层厚度变化研究

基于MODIS温度数据,采用TTOP模型和Stefan公式模拟了青藏高原地区的冻土分布并计算了活动层厚度,并与地面观测结果进行了对比。结果表明：2003—2019年青藏高原多年冻土面积为1.01×10⁶ km²;多年冻土活动层厚度区域平均值为1.79 m, 活动层厚度区域平均的变化率为3.67 cm/10a,且草甸地区的变化率明显大于草原地区,5100~5300 m高程带的活动层厚度变化速率最大。     

土地利用/覆被变化的环境效应研究进展与动向

土地利用／覆被变化产生的环境问题已引起人类社会的广泛关注,深入研究这些问题具有重要的理论和实践意义。在简要回顾土地利用／覆被变化对大气环境、土壤环境和水环境影响已有研究的基础上,结合中国研究的实际,分析了中国土地利用／覆被变化的环境效应研究中存在的问题,并对今后的研究趋势做了讨论。     

Artificially frozen ground and related engineering technology in Japan

Since the 1970's, frozen ground has been developing near the Tokyo Bay area around liquefied natural gas(LNG) inground storage tanks. For disaster prevention purposes, the tanks are constructed below the ground surface. Since the temperature of the liquid stored in the tanks is -162℃ the soil surrounding the tanks freezes. Since this frozen ground has existed for almost half a century, we have permafrost near Tokyo. The development of artificial frozen ground may cause frost heaving, resulting in frost heave forces that may cause structural damage of adjacent LNG in-ground storage tanks.Therefore, the demand for frozen ground engineering increased and consequently we now have advanced technology in this area. Fortunately, we use this engineering technology and artificial ground freezing for civil engineering, especially in big and crowded cities like Tokyo. This paper provides a summary of the testing apparatus, test methods, and assessment methods for frost heaving.     

滨海滩涂土壤有机碳演变驱动因子框架

通过归纳、总结前人大量的研究成果,从土壤有机碳演变的尺度约束框架、滩涂土壤有机碳的核心控制因子以及演变的驱动因素3个方面进行总结。结果表明：①目前形成的监测技术约束下的碳库研究体系,其研究的结果忽视了机理性认识的未来需要,这对于应对未来气候变化条件下的滩涂湿地碳库变化风险稍显不足; ② 滩涂土壤有机碳演变的核心控制因子有泥沙、地貌与埋藏速率、植被与农业活动。滩涂围垦后的农业活动类型与方式是滩涂开发后影响土壤有机碳演变的核心要素,远远高于自然滩涂中的自然主导因子; ③ 不同因素在不同时空尺度上会对滩涂有机碳演变起到重要影响,其中,土地利用/覆被对于有机碳的影响机制是需要重点关注的核心命题; ④ 小尺度、长时间尺度有机碳循环机制的研究需要加强,同时,综合考量要素的时空尺度特性及其技术手段的提升,更加注重过程研究对于指导未来滩涂土壤有机碳研究更具有现实意义。     

Predictive mapping of soil total nitrogen at a regional scale: A comparison between geographically weighted regression and cokriging

Accurately mapping the spatial distribution of soil total nitrogen is important to precision agriculture and environmental management. Geostatistical methods have been frequently used for predictive mapping of soil properties. Recently, a local regression method, geographically weighted regression (GWR), got the attention of environmentalists as an alternative in spatial modeling of environmental attributes, due to its capability of incorporating various auxiliary variables with spatially varied correlation coefficients. The objective of this study is to compare GWR and ordinary cokriging (OCK) in predictive mapping of soil total nitrogen (TN) using multiple environmental variables. 353 soil Samples within the surface horizon of 0–20 cm in a study area were collected, and their TN contents were measured for calibrating and validating the GWR and OCK interpolations. The environmental variables finally chosen as auxiliary data include elevation, land use types, and soil types. Results indicate that, although OCK is slightly better than GWR in global accuracy of soil TN prediction (the adjusted R² for GWR and OCK are 0.5746 and 0.6858, respectively), the soil TN map interpolated by GWR shows many details reflecting the spatial variations of major auxiliary variables while OCK smoothes out almost all local details. Geographically weighted regression could account for both the spatial trend and local variations, whilst OCK had difficulties to capture local variations. It is concluded that GWR is a more promising spatial interpolation method compared to OCK in predicting soil TN and potentially other soil properties, if a suitable set of auxiliary variables are available and selected.     

Analysis of temperature field characteristics based on subgrade site measurements of Harbin-Qiqihar High-speed Railway in a deep seasonal frozen soil region

Recent years have seen a large number of high-speed railways built and will be built in seasonal frozen soil regions of China. Although high-speed railways are characterized by being fast, comfortable and safe, higher standards for deformation of the railways' frozen subgrade are required. Meanwhile, changes in subgrade soil temperatures are the main factors affecting the deformation of frozen subgrade. Therefore, this paper selected typical test subgrade sections of the Harbin–Qiqihar Line, a special line for passenger transport built in the deep seasonal frozen soil regions of China, to monitor field temperatures. Also, the temperature changing laws of railways' subgrade in this region was analyzed by using testing data, the aim of which is to provide a technical support for future design and construction of buildings and structures in a deep seasonal frozen soil region.     

耕地土壤速效钾含量的空间预测方法研究

利用插值方法进行土壤属性的空间预测是土壤学科的研究热点之一,以土壤发生学相关信息作为辅助变量的克里格空间插值方法则少有研究。该文以成土母质多样的湖南省石门县为例,基于GS+、ArcGIS和Matlab,结合成土母质信息的克里格(PMK)插值方法,对研究区土壤速效钾空间分布进行了预测。结果表明,PMK法较好地解决了因成土母质间速效钾含量差异给预测带来的误差,预测精度较反距离权重(IDW)、普通克里格(OK)法分别提高了21.68%、16.43%;PMK法制作的空间预测图中速效钾分布突变而非渐变,较IDW、OK预测结果接近研究区实际情况,进而证明在成土母质较为复杂的地区,PMK法适合对土壤速效钾含量的预测。     

Application of p-y approach in analyzing pile foundations in frozen ground overlying liquefiable soils

Two major earthquakes in Alaska, namely the 1964 Great Alaska Earthquake and the 2002 Denali Earthquake, occurred in winter seasons when the ground crust was frozen. None of the then-existing foundation types was able to withstand the force from the lateral spreading of frozen crust. This paper presents results from the analysis of pile foundations in frozen ground overlying liquefiable soil utilizing the Beam-on-Nonlinear-Winkler-Foundation (BNWF) (or p-y approach). P-multipliers were applied on traditional sandy soil p-y curves to simulate soil strength degradation during liquefaction. Frozen soil p-y curves were constructed based on a model proposed in a recent study and the frozen soil mechanical properties obtained from testing of naturally frozen soils. Pile response results from the p-y approach were presented along with those from fluid-solid coupled Finite Element (FE) modeling for comparison purpose. Finally, the sensitivity of pile response to frozen soil parameters was investigated and a brief discussion is presented.     

现代种植业系统能流转化效率分析及评价——以河北省栾城县为例

能量转化效率是评价农业资源利用效率的一个综合性指标。本文在分析现代种植业系统特点的基础上,以河北省栾城县为例,研究了现代种植业系统的投入和生产特点。对系统能流分析结果表明,进入９０年代后,随着人工辅助能特别是工业辅助能投入的增加,系统能效逐渐降低。因此改进系统生产结构和投入结构,充分利用现代生物和工程技术,提高农业资源的利用效率,是实现现代农业持续发展的关键。     

Freezing and thawing effects of sand-silt mixtures on elastic waves

Freezing and thawing during the winter season change soil properties such as density. The density change in the particulate media influences soil stiffness. In addition, freezing of partially or fully saturated soils changes the soil matrix from a particulate media to a continuum. The goal of this study is to investigate the cyclic freezing and thawing effects on elastic waves. Sand-silt mixtures with 10% silt fraction in weight and 40% saturation are prepared. The sand-silt mixtures are placed in a nylon cell, onto which a pair of bender elements and a pair of piezoelectric disk elements are installed for the measurement of shear and compressional waves, respectively. The temperature of the mixtures decreases from 20°C to 10°C to freezing. The frozen sample is gradually thawed at room temperature (20°C). These freezing-thawing processes are repeated three times. The test result shows that the shear and compressional wave velocities significantly increase when the specimen is frozen. When the temperature is greater than 0°C, the elastic wave velocities are lower during thawing than during freezing due to soil structure change. This study demonstrates that soil structure change during the winter season may be effectively estimated from elastic waves.     

海岸沙地利用变化及其环境效应研究进展

地处全球变化敏感地区的海岸沙地的利用变化及其环境效应日益受到关注。文章通过对海岸沙地利用及其变化研究的发展历程,海岸沙地利用变化研究的案例与技术方法,海岸沙地利用变化所引起的大气环境、水环境、土壤环境、生物环境等方面的环境效应研究等文献的梳理和总结,对国内外海岸沙地利用变化及其环境效应的研究进展进行了综述,并提出了今后研究的主要方向：海岸沙地利用变化未来发展的情景模拟、海岸沙地利用演变驱动机理的定量分析、海岸沙地利用的整体生态环境效应研究、海岸沙地防护林地的合理开发与布局等。