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1.
艾比湖地区冻融作用对梭梭群落土壤酶活性及微生物数量的影响 总被引：3，自引：0，他引：3
冻融作用对酶和微生物活性具有重要影响,进而影响植物群落的生长发育。为深入了解荒漠优势种梭梭群落冬季土壤生态过程,于2012年10月~2013年10月,对土壤冻融期、冻结期、融冻期和生长季的艾比湖典型样地进行野外实地观测、采样和室内分析。通过对比分析不同冻融阶段土壤含水量、pH值、有机质、全氮、酶活性和微生物数量的变化特征。结果表明:(1)土壤含水量,融冻期 >冻结期 >冻融期 >生长季,土壤pH值,生长季 >融冻期 >冻融期 >冻结期,各土层土壤含水量以浅层土表现最为显著(P <0.05),不同冻融阶段各土层pH值差异性较大,冻融期、冻结期和生长季表层土壤pH值较大,融冻期浅层土壤pH值较大。(2)土壤有机质和全氮含量的波动状况相似,分别在融冻期和生长季呈现波峰和波谷,不同土层间全氮和有机质含量差异性较小,以冻融期和生长季表现最为显著(P <0.05)。(3)土壤酶活性的变化中,过氧化氢酶、脲酶和蛋白酶在融冻期含量最大,冻融期次之,蔗糖酶在冻结期活性最大,土壤微生物数量的变化以融冻期最大,除此之外,各冻融阶段细菌和放线菌占主导,真菌含量相对较少。(4)冻融循环次数分布于冻融期和融冻期,对土壤酶活性和微生物数量具有一定的影响,致使融冻期土壤各因子大于冻融期。 相似文献
2.
冻融条件下土壤中水盐运移规律模拟研究 总被引：16，自引：0，他引：16
冻融作用是土壤盐碱化独特的形成机制,冻融条件下土壤中盐分迁移是水分对流、浓度梯度、温度梯度、不同溶质、土壤结构及质地等因素作用下的综合结果,温度是导致土壤中水分与盐分迁移的驱动力。在土壤冻融过程中,水分和盐分的两次迁移过程构成了特殊的水盐运动规律。在冻融过程中,土壤剖面结构发生变异,形成冻结层、似冻结层和非冻结层。冻结带土水势降低导致水分不断向冻层迁移,冻结缘以下的盐分同步向上运移,整个冻层的土壤含盐量明显增加;在融化过程中,随着地表蒸发逐渐强烈,使冻结过程中累积于冻结层中的盐分,转而向地表强烈聚集,使表层的盐分含量急剧上升。当冻结层未融通之前,尚未融化的冻层起到隔水的作用,不但阻止顶部融水向下层渗透,而且隔断了与下层水的联系。模拟实验结果充分证明了中国北方冻融区域土壤盐碱化的发生过程,为有效防治土壤盐碱化提供了理论依据。 相似文献
3.
区域尺度蒸散发遥感估算——反演与数据同化研究进展 总被引：3，自引：0，他引：3
遥感技术近年来在估算区域尺度蒸散发中应用广泛。不同方法在驱动数据、模型机理和适用范围往往存在很大差别。鉴于此,阐述了基于传统方法空间尺度扩展的遥感模型,经验统计公式,特征空间法,单源、双源垂向能量平衡余项法等几类的遥感蒸散发反演方法,简要介绍了三温模型、非参数化模型、半经验模型、集成模型等常用模型。同时,分析了遥感数据同化实现连续估算区域蒸散发的主要思路,综述了基于能量平衡和基于复杂过程模型的数据同化的原理、方法演进及常用同化算法等。最后,探讨了各类区域蒸散发遥感方法的优劣、展望了模型机理完善、不确定性研究、结果验证等与蒸散发直接反演和数据同化相关的研究方向。 相似文献
4.
5.
土壤盐渍化遥感应用研究进展 总被引：31，自引：4，他引：31
文章从地面数据的调查、盐渍土影象的目视判读特征、光谱特征和土壤盐渍化区域的植被特征以及多光谱、高光谱遥感技术等方面综述国内外应用遥感数据探测土壤盐渍化程度及其制图的研究。利用数字图象并结合野外调查数据进行目视解译和计算机自动解译、图象变换提取盐渍土信息;结合G IS方法在分类中加入非遥感数据来提高分类精度;在研究盐渍土的光谱特征的基础上应用高光谱技术定量或半定量地提取盐渍土信息。这都是制定综合治理措施、决定土地利用方向的关键,也是进行区域土壤盐渍化动态预报的重要依据。 相似文献
6.
地学应用中的遥感图像处理若干问题的分析 总被引：5，自引：3，他引：5
遥感技术在地理学应用中是如何从遥感影像上直观、准确的得到所需的信息,为本专业服务。文章从地学应用部门在进行遥感影像处理时遇到的几个问题:多光谱数据的选取与合成;多源信息的复合;新型图像分类器的应用;专题提取的精度等方面的进展作了分析。 相似文献
7.
Douglas G. Goodin 《自然地理学》2013,34(6):557-572
Increased use of remotely sensed data for estimation of land-surface climatological variables such as the radiation and energy balance has underscored the need to understand errors inherent in remote sensing systems. The effects of viewing geometry on the signal received at the sensor have been examined for a variety of surface types, but systematic study of how sensor viewing geometry may introduce error into remote measurements of surface climate parameters is lacking. In this paper, close-range remote sensing is used to assess error caused by viewing geometry in remote measurements of net radiation, an important surface climate variable. Estimates of net radiation were made by inserting remotely sensed values of albedo and surface temperature into the surface radiation budget equation. Two contrasting surfaces, one vegetated and one bare, were evaluated at seven view angles and five azimuth angles. The remote net radiation measurements for each combination of view and azimuth angle then were compared to reference measurements to assess error. Results indicate that, under cloud-free conditions, view angle can affect measurement accuracy substantially, and that off-nadir view angles ranging from 15° to 30° in the forward-scatter direction are optimal. The potential impact of these findings on studies of the spatial variation of the surface radiation budget from spaceborne remote sensing platforms is discussed. [Key words: land-surface climatology, remote sensing, radiation budget, net radiation.] 相似文献
8.
基于水热变化的青藏高原土壤冻融过程研究进展 总被引：1，自引：0，他引：1
青藏高原近地层土壤冻融过程是高原地表最显著的陆面特征之一,也是判断冻土发育、存在以及反映气候变化的重要指标。近地层土壤昼夜、季节性的冻结、融化会导致青藏高原陆—气间能水平衡的变化甚至异常,从而显著影响高原地表水文过程、生态环境、碳氮循环以及高原及其周边区域的天气和气候系统。论文从观测、模拟以及对气候的影响3个角度来探讨1990年以来青藏高原土壤冻融过程的最新研究进展。结果表明：① 在一个完整的年冻融循环过程中,近地表各层土壤大体都经历了夏季融化期、春秋季融化—冻结期、冬季冻结期4个阶段。受局地因素的影响,不同站点的冻结或消融起止时间、速率、类型均有差异。② 多年冻土区和季节冻土区的日冻融循环过程差异较大,主要体现在日冻融循环持续时间上。③ 不同陆面模式都可以很好地抓住冻融过程中物理量的时空变化,但都需要针对高原陆面过程的特点进行参数化改进。④ 规避不稳定的迭代计算并根据热力学平衡方程确定冻融临界温度可以改进不合理的冻融参数化方案。基于已有研究回顾,发现增加高质量的观测站,利用卫星遥感等多种手段来反演高原土壤冻融过程以及加强陆面模式与区域气候模式和全球气候模式的耦合,并立足于高原冻融过程的特点发展相适应的参数化方案以及模拟结构的调整,能够有助于高原冻融过程的模拟。 相似文献
9.
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. 相似文献
10.
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 总被引：5，自引：1，他引：4
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。 相似文献
11.
基于C5.0决策树分类算法的ETM+影像信息提取 总被引：3，自引：1，他引：3
利用C5.0决策树算法对ETM 影像进行信息提取,通过与其他分类方法提取结果的对比,得出C5.0决策树分类算法精度较高。大气校正与数据融合可明显提高分类精度,利用经过NDVI、NDBI、缨帽变换处理后的影像组合数据进行信息提取可进一步提高分类精度。研究发现,C5.0决策树算法用未处理的资料生成决策树的效果较差,而经大气校正和数据融合后计算出NDVI、NDBI及缨帽变换的前3个分量的组合数据生成的决策树深度最小,并且分类精度最高。 相似文献
12.
基于遥感的城市热岛效应研究 总被引：15，自引：0，他引：15
热红外遥感和气候学的交叉融合为城市热岛效应提供了新的研究方法。从城市热岛的空间分布与土地利用类型、植被覆盖关系、人为热关系以及城市热岛效应演变4方面分析热红外遥感在城市热岛研究中的应用现状;探讨目前存在的两个主要问题:城市地物真实温度难以获取,遥感和气候模型结合不密切;提出遥感和气候模型结合以及多平台、多尺度、多角度遥感的综合应用等是城市热岛效应遥感研究的发展趋势。 相似文献
13.
东北黑土区土壤剖面地温和水分变化规律 总被引：3，自引：1，他引：2
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。 相似文献
14.
Problems in the interpretation of passive optical remote sensing data obtained by telespectrometric measurements on board a research vessel (or aircraft) are discussed. Two methods are considered: (1) The correlation method, where correlative relationships between the remotely sensed spectra and concentrations of optically active substances in the water are determined and corresponding regression formulae found; (2) the similarity method, where the remotely sensed spectrum is compared with the multitude of spectra obtained by means of model calculations. The application of these methods and analysis of the results are made using our remote and in situ data. It is found that the correlation method is far from being general (the regression parameters depend on the location, season and weather conditions), but it has the advantage of being applicable without the need to describe the aquatic environment by a theoretical model. The similarity method is much more general but involves difficulties in including the optical properties of the aquatic environment in the theoretical model, especially the backscattering properties of several types of suspended matter in the water bodies.
Some aspects of detecting oil-slick pollution on the sea surface by means of passive optical remote sensing methods are discussed and corresponding examples are shown. 相似文献
Some aspects of detecting oil-slick pollution on the sea surface by means of passive optical remote sensing methods are discussed and corresponding examples are shown. 相似文献
15.
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. 相似文献
16.
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. 相似文献
17.
Lagoon berms in western Alaska are difficult to design and build due to limited resources, high cost of construction and materials, and warm permafrost conditions. This paper explores methods to treat locally available frozen materials and use them for berm construction. The goal is to find an optimized mix ratio for cement and additives that can be effective in increasing the strength and decreasing the thaw settlement of an ice-rich frozen silty soil. Soil of similar type and ice content to the permafrost found at a project site in Eek, Alaska is prepared in a cold room. The frozen soil is pulverized and cement, additives and fibers are added to the samples for enhancing shear strength and controlling thaw settlement. Thaw settlement and direct shear testsare performed to assess strength and settlement characteristics. This paper presents a sample preparation method, data from thaw settlement and direct shear tests, and analyses of the test results and preliminary conclusions. 相似文献
18.
Evaluation of approaches for forest cover estimation in the Pacific Northwest, USA, using remote sensing 总被引：3，自引：0，他引：3
The transformation of land cover, in particular coniferous forest, constitutes one of the most notable agents of regional-to-global-scale environmental change. Remote sensing provides an excellent opportunity for providing forest cover information at appropriate spatial and temporal scales. The optimal exploitation of remote sensing relies on the link between known forest cover and the remotely sensed dataset. This paper explores the accuracy of three methods – vegetation indices, regression analysis and neural networks – for estimating coniferous forest cover across the United States Pacific Northwest. All methods achieved a similar accuracy of forest cover estimation. However, in view of the benefits and limitations of each, the neural network approach is recommended for future consideration. 相似文献
19.
土壤砂粒含量是表征土壤质量的重要指标,探索建立基于高光谱遥感的区域土壤砂粒含量反演方法对区域土壤质量监测具有重要意义。通过野外采集的高光谱数据与MODIS影像相结合,遴选出土壤砂粒含量的敏感波段与反演方程,进行干旱区裸地土壤砂粒含量遥感反演研究。结果表明：430 nm为土壤砂粒含量的敏感波段,原始光谱经变换后的数值与土壤砂粒含量的相关系数在430 nm处达到最大值0.76;基于MODIS第3波段中心波长460 nm处的土壤原始光谱的反演精度最高,达到89.30%,与实际情况吻合较好,表明MODIS第3波段可以应用于干旱区裸地土壤砂粒含量的遥感反演。 相似文献
20.
陇西黄土高原陆面蒸散的遥感研究 总被引：18，自引：0，他引：18
该文以陆面能量平衡过程为基础,基于定量遥感的理论,提出了适合半干旱区(陇西黄土高原)的陆面蒸散估算遥感模型(SEBS)。结合该区域的NOAA/AVHRR数据、气象观测数据、土地利用数据和地形高程(DEM)数据,依据定量遥感的理论和技术,计算反照率、陆面温度、植被指数和地表比辐射率四个重要地表特征参数。应用SEBS模型,估算了该区域的陆面蒸散量。结果表明：该研究具有较好的理论和实践意义,为陆面过程、植被生产、生态环境保护与生态重建等研究提供科学依据。 相似文献