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1.
吉林查干湖水体叶绿素a含量高光谱模型研究 总被引：5，自引：1，他引：4
叶绿素a含量能够在一定程度上反映水质状况,高光谱遥感可有效反演叶绿素a含量.该研究通过分析水体叶绿素a浓度与其高光谱反射特征之间的相关关系,采用单波段相关分析、波段比值、微分光谱和神经网络模型等多种算法建立了叶绿素a高光谱定量模型.结果表明:叶绿素a与单波段光谱在蓝、绿波段相关系数较低,而在红光与近红外波段有明显提高,微分光谱也表现出同样的趋势;反射率比值算法模拟效果好于线性回归法;神经元网络模型可以大大提高实测光谱数据的反演能力,确定性系数高达0.95.这为今后利用星载高光谱传感器在查干湖进行叶绿素a浓度大面积遥感反演提供了研究基础. 相似文献
2.
基于环境一号卫星高光谱遥感数据的巢湖水体叶绿素a浓度反演 总被引：5，自引：0，他引：5
三波段模型是基于生物光学模型构建的叶绿素a浓度反演半分析模型,是目前反演内陆富营养化浑浊水体叶绿素a浓度效果较好的方法.本文通过星地同步实验,分析巢湖水体各组分光谱特征,分别基于地面实测数据与环境一号卫星高光谱遥感数据建立三波段模型反演巢湖水体叶绿素a浓度.结果表明,由于特征波段在不同数据源的位置不同,导致了两个模型波段选择及反演精度的差异.因此,只有在充分考虑遥感数据的光谱特征的条件下,分析遥感信息理论和实际图幅影像有效结合在一起的地物信息,才能进一步优化三波段模型的波段选择,实现遥感数据定量反演水体叶绿素a浓度的目标. 相似文献
3.
应用实测光谱估算千岛湖夏季叶绿素a浓度 总被引：4，自引：2，他引：2
依据2010年8月的实测数据构建了千岛湖水体夏季叶绿素a浓度的实测光谱数据估算模型,并进行了验证.利用ASD FieldSpec3野外光谱仪获取高光谱数据,计算水体离水辐亮度和遥感反射率.通过寻找反演水体叶绿素a浓度的高光谱敏感波段,采用单波段相关分析、波段比值、微分光谱、三波段模型、BP人工神经网络等多种算法进行比较分析,结果表明:叶绿素a浓度与单波段光谱反射率的相关性不大;596 nm和489 nm波长处反射率比值、545 nm处光谱一阶微分与叶绿素a浓度均呈较显著相关,估测模型决定系数R2分别为0.782、0.590,RMSE分别为0.89、1.98μg/L;三波段模型的反演结果优于传统的波段比值和一阶微分法,R2为0.838,RMSE为0.71μg/L;神经网络模型大大提高了叶绿素a浓度的反演精度,R2高达0.942,RMSE为0.63μg/L.本研究为今后在千岛湖水域的夏季相邻月份进行叶绿素a浓度大范围遥感反演研究奠定了基础. 相似文献
4.
基于半分析模型的波段最优化组合反演混浊太湖水体叶绿素a 总被引：5，自引：0，他引：5
内陆水体叶绿素a浓度定量反演是水质遥感的热点与难点.本文基于对内陆水体叶绿素a、悬浮物、溶解有机物与水分子的光谱特征分析,从半分析生物光学模型出发,利用太湖实测的水面 ASD 高光谱遥感数据三波段组合,进行迭代优化,得到与叶绿素浓度密切相关而受悬浮物与黄色物质影响小的最优波段组合模型,反演精度较高,其决定系数和均方根误差分别为 0.8358、3.816mg/m3,该方法可以有效地反演高浓度悬浮物主导光学特性的水体叶绿素a浓度. 相似文献
5.
基于反射光谱的太湖北部叶绿素a浓度定量估算 总被引：2，自引：0，他引：2
利用地物光谱仪研究了太湖水体的反射光谱特征与叶绿素a浓度之间的定量关系,结果表明太湖水体的叶绿素a浓度可以用720 nm附近的反射率估算,同时也可以用806 nm和571 nm两个波段的反射率比值来估算,前者建立的估算模型具有较好的通用性,而后者只能较好的估算<10μg/L的叶绿素a浓度;通过对光谱微分的分析,发现叶绿素a浓度与690 nm附近的一阶微分和702 nm附近的二阶微分相关性最好,但基于反射光谱一阶微分的叶绿素a浓度估算模型,并没有显著的提高太湖叶绿素a浓度的估测精度,二阶微分后的估测精度好于一阶微分,但其估测精度仍没有利用720 nm反射光谱的反演模型高．太湖水体的叶绿素a浓度可以利用720 nm附近的反射光谱有效地估算． 相似文献
6.
太湖水体叶绿素浓度反演模型适宜性分析 总被引：2，自引：0，他引：2
为确定适合太湖水体叶绿素的反演算法,为同类卫星数据的建模和应用提供参考,本文根据太湖2007年11月、2009年4月和2011年8月实测水质参数以及同步光谱数据,结合水色遥感传感器MODIS、MERIS、GOCI及我国自主发射的HJ-1号卫星CCD传感器波段参数,基于差值模型、比值模型、三波段模型及APPEL模型,分别建立太湖水体叶绿素浓度反演模型,并分析模型的适宜性.结果显示,基于不同传感器数据APPEL模型的决定系数为0.7308~0.8107,模型相对误差为15%~24%,均方根误差为21%~32%;三波段模型基于不同传感器数据拟合的决定系数为0.6014~0.7610,相对误差为28%~36%,相对均方根误差为39%~46%;差值模型决定系数为0.4954~0.7244,相对误差为39%~53%,相对均方根误差为51%~72%;比值模型决定系数为0.4918~0.7098,相对误差为41%~55%,相对均方根误差为56%~75%.相比较而言,APPEL模型的稳定性较强,适合于不同传感器数据的太湖水体叶绿素浓度的反演.此外,相应不同传感器波段位置、波段宽度对模型反演的精度和稳定性的影响也不同,当波段位置接近叶绿素特征波长时,较窄的波宽有利于模型精度的提高,波段位置和叶绿素浓度特征波长相差较大时,合理增加波谱范围有利于叶绿素特征信息的获取. 相似文献
7.
2007年8月至2008年9月,对厦门两个淡水水体(芙蓉湖、厦大水库)的叶绿素浓度和遥感反射率(Rrs)进行了连续观测.在叶绿素浓度6-322mg/m3的范围,Rrs光谱出现显著的近红外反射峰,中心位置在700-710nm之间,较之通常的荧光峰中心(683nm)向长波方向偏离.该峰在厦大水库始终出现在700nm,但在芙蓉湖存在时间变化,随着叶绿素浓度的增加,由705红移到710nm.由此,仿MODIS荧光高度(FLH)的定义,定义该峰的高度(简写为REH),对于水库和美蓉湖中心波段分别确定为700和710nm.REH与叶绿素浓度呈现显著相关,美蓉湖REH=0.0161g(chl)-7.8×10-6(R2=0.79,n=41),水库REH=0.0001chl+0.0002(R2=0.74,n=32).可见对十高散射的淡水藻华水体,可以并且需要通过改进FLH的波段选择,基于更长波段处的近红外峰的高度探测叶绿素浓度. 相似文献
8.
基于叶绿素荧光峰特征的浑浊水体悬浮物浓度遥感反演 总被引：4，自引：0，他引：4
内陆水体光学特性复杂,其水质参数遥感反演是当前环境遥感研究的热点与难点.2004年10月在太湖实测了67个站点的遥感反射率与相应站点水质参数浓度,通过对水体反射率光谱的分析发现,秋季太湖悬浮物主导了水体光学特性,叶绿素荧光峰的特征主要体现为悬浮物浓度的变化.据此建立了基于水面实测岛光谱遥感反射率数据的叶绿素荧光峰特征与悬浮物浓度之间的拟合关系,发现二者具有很好的响应关系.具体分析了叶绿素荧光峰绝对高度、基线高度、归一化高度(分别归一化到560nm附近最大反射率波段与近红外810nm附近最大反射率波段)及荧光峰积分面积(包括积分总面积、基线以下面积与基线以上面积)等儿种光谱特征与悬浮物浓度之间的关系,其相关系数(R2)分别为0.8822、0.7483、0.8901、0.8547、0.8927、0.8877、0.8632,平均相对误差分别为27.25%、41.03%、27.11%、25.75%、24.91%、25.47%、27.54%.总体反演精度较高,其中总积分面积法效果最好,基线高度法效果最差,而叶绿索荧光峰波段的位移与悬浮物浓度之间不存在明显的相关性.研究结果表明叶绿素荧光峰特征在浑浊内陆水体悬浮物浓度信息提取中具有很好的应用前景,该方法可为浑浊的二类水体悬浮物遥感反演提供了一个新思路. 相似文献
9.
MERIS影像水环境遥感大气校正算法评价——以鄱阳湖叶绿素a浓度反演为例 总被引：1，自引：0，他引：1
MERIS是2002年发射的在轨运行近10年的ENVISAT-1卫星上搭载的主要传感器之一,在波段设置和辐射灵敏度等方面有非常突出的优势,能够较好地运用于Ⅱ类水体叶绿素a浓度反演,但Ⅱ类水体的大气校正仍然是亟待解决的一个关键问题.以我国第一大淡水湖——鄱阳湖为研究区域,采用FLAASH、6S、BEAM和QUAC共4种大气校正算法对2005和2011年具有同步实测光谱数据的鄱阳湖ENVISAT-1卫星MERIS影像进行大气校正处理,并对12种叶绿素a浓度反演模型的波段组合因子进行大气校正效果的对比分析.结果表明:(1)4种大气校正中,大气校正结果精度由高到低表现为FLAASH6SBEAMQUAC,平均相对误差分别为31.13%、31.88%、69.48%和42.64%;决定系数(R2)分别为0.60、0.57、0.38和0.24;(2)在12种叶绿素a浓度反演模型的波段组合因子中,FLAASH得到的结果最优,其次是6S,BEAM和QUAC最差,在FLAASH算法中,由665、708和753 nm 3个波段遥感因子((Rrs(510)/[Rrs(443)/Rrs(560)])组成的模型精度最高,平均相对误差为25.12%,R2为0.74.建议采用FLAASH大气校正结果组成这个波段组合进行鄱阳湖叶绿素a浓度反演. 相似文献
10.
现有水色卫星主要是针对大洋清洁水体设计,内陆浑浊水体多数波段经常饱和;而发展可以业务化运行的内陆水体叶绿素a算法,为生产实践服务,一直是水色遥感的重点和难点之一.利用2013年巢湖星地同步数据(N=55),通过经验正交函数(empirical orthogonal function,EOF)分析方法,选用MODIS唯一不饱和的4个波段(469、555、645、859 nm)数据进行分解,然后回归建模;并使用第三方独立的巢湖实测数据(N=40)进行验证(R2=0.63,URMSE=85.46%).结果表明:该算法用于MODIS影像上,空间分布合理,季节差异明显,且在高悬浮物水体、不同气溶胶条件下均有很好的抗扰动性.实践证明EOF算法可以应用于业务化运行的内陆水体叶绿素a浓度估算,并对其他水色参数反演具有一定的借鉴意义. 相似文献
11.
Diffusive mass exchange of non‐reactive substances in dual‐porosity porous systems – column experiments under saturated conditions 
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下载免费PDF全文 Diffusive mass exchange into immobile water regions within heterogeneous porous aquifers influences the fate of solutes. The percentage of immobile water is often unidentified in natural aquifers though. Hence, the mathematical prediction of solute transport in such heterogeneous aquifers remains challenging. The objective of this study was to find a simple analytical model approach that allows quantifying properties of mobile and immobile water regions and the portion of immobile water in a porous system. Therefore, the Single Fissure Dispersion Model (SFDM), which takes into account diffusive mass exchange between mobile and immobile water zones, was applied to model transport in well‐defined saturated dual‐porosity column experiments. Direct and indirect model validation was performed by running experiments at different flow velocities and using conservative tracer with different molecular diffusion coefficients. In another column setup, immobile water regions were randomly distributed to test the model applicability and to determine the portion of immobile water. In all setups, the tracer concentration curves showed differences in normalized maximum peak concentration, tailing and mass recovery according to their diffusion coefficients. These findings were more pronounced at lower flow rates (larger flow times) indicating the dependency of diffusive mass exchange into immobile water regions on tracers' molecular diffusion coefficients. The SFDM simulated all data with high model efficiency. Successful model validation supported the physical meaning of fitted model parameters. This study showed that the SFDM, developed for fissured aquifers, is applicable in porous media and can be used to determine porosity and volume of regions with immobile water. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
12.
We determine the relevance of Multi-Rate Mass Tansfer (MRMT) models (Haggerty and Gorelick, 1995) to general diffusive porosity structures. To this end, we introduce Structured INteracting Continua (SINC) models as the combination of a finite number of diffusion-dominated interconnected immobile zones exchanging with an advection-dominated mobile domain. It directly extends Multiple INteracting Continua framework (Pruess and Narasimhan, 1985) by introducing a structure in the immobile domain, coming for example from the dead-ends of fracture clusters or poorly-connected dissolution patterns. We demonstrate that, whatever their structure, SINC models can be made equivalent in terms of concentration in the mobile zone to a unique MRMT model. We develop effective shape-free numerical methods to identify its few dominant rates, that comply with any distribution of rates and porosities. We show that differences in terms of macrodispersion are not larger than 50% for approximate MRMT models with only one rate (double porosity models), and drop down to less than 0.1% for five rates MRMT models. Low-dimensional MRMT models accurately approach transport in structured diffusive porosities at intermediate and long times and only miss early responses. 相似文献
13.
The assumptions and analysis of Part 1 are extended to the three model soil-water profiles having different immobile-water contents up to 0.08 m3 m?3. Concentration profiles in the mobile zone obtained with a constant dispersion coefficient are compared with those calculated with the same dispersion coefficient and no immobile water. The average concentration profiles were calculated from the concentration of the solution in both the mobile and immobile phases. Increasing the immobile-water content decreased and shifted the average concentration profiles further into the soil. The values of the dispersion coefficient calculated with the immobile-water fraction ignored, were found to be water content dependent and many times greater than that of the input dispersion coefficient. 相似文献
14.
Spreading of floating particles by Langmuir circulation 总被引：1，自引：0，他引：1
S.A. Thorpe 《Marine pollution bulletin》2009,58(12):1787-1791
Particles floating on the sea surface, in particular buoyant algae, are drawn into bands by the converging flow between neighbouring Langmuir cells. Floating bands subsequently amalgamate as a result of Langmuir turbulence. Simple models are developed to describe the rearrangement and dispersion of the floating particles. If the production of floating particles has ceased, the mean separation of the bands of particles increases with time and eventually becomes unrelated to the mean distance between the lines of convergence resulting from Langmuir circulation. The concentration of particles in the bands, proportional to the width of bands, and the separation of bands with a given concentration of particles, both increase with time. Care is needed in estimating the width of Langmuir cells to distinguish between surface bands of floating material that is continuously being produced and bands made visible by some earlier, but discontinued, generation. An alternative mechanism for the generation of dense bands of floating algae is proposed. 相似文献
15.
This study formulates and analyzes continuous time random walk (CTRW) models in radial flow geometries for the quantification of non-local solute transport induced by heterogeneous flow distributions and by mobile–immobile mass transfer processes. To this end we derive a general CTRW framework in radial coordinates starting from the random walk equations for radial particle positions and times. The particle density, or solute concentration is governed by a non-local radial advection–dispersion equation (ADE). Unlike in CTRWs for uniform flow scenarios, particle transition times here depend on the radial particle position, which renders the CTRW non-stationary. As a consequence, the memory kernel characterizing the non-local ADE, is radially dependent. Based on this general formulation, we derive radial CTRW implementations that (i) emulate non-local radial transport due to heterogeneous advection, (ii) model multirate mass transfer (MRMT) between mobile and immobile continua, and (iii) quantify both heterogeneous advection in a mobile region and mass transfer between mobile and immobile regions. The expected solute breakthrough behavior is studied using numerical random walk particle tracking simulations. This behavior is analyzed by explicit analytical expressions for the asymptotic solute breakthrough curves. We observe clear power-law tails of the solute breakthrough for broad (power-law) distributions of particle transit times (heterogeneous advection) and particle trapping times (MRMT model). The combined model displays two distinct time regimes. An intermediate regime, in which the solute breakthrough is dominated by the particle transit times in the mobile zones, and a late time regime that is governed by the distribution of particle trapping times in immobile zones. These radial CTRW formulations allow for the identification of heterogeneous advection and mobile-immobile processes as drivers of anomalous transport, under conditions relevant for field tracer tests. 相似文献
16.
Changes in the water table level result in variable water saturation and variable hydrological fluxes at the interface between the unsaturated and saturated zone. This may influence the transport and fate of contaminants in the subsurface. The objective of this study was to examine the impact of a decreasing and an increasing water table on solute transport. We conducted tracer experiments at downward flow conditions in laboratory columns filled with two different uniform porous media under static and transient flow conditions either increasing or decreasing the water table. Tracer breakthrough curves were simulated using a mobile–immobile transport model. The resulting transport parameters were compared to identify dominant transport processes. Changes in the water table level affected dispersivities and mobile water fractions depending on the direction of water table movement and the grain size of the porous media. In fine glass beads, the water flow velocity was similar to the decline rate of the water table, and the mobile water fraction was decreased compared with steady‐state saturated conditions. However, immobile water was negligible. In coarse glass beads, water flow was faster because of fingered flow in the unsaturated part, and the mobile water fraction was smaller than in the fine material. Here, a rising water table led to an even smaller mobile water fraction and increased solute spreading because of diffusive interaction with immobile water. We conclude that changes of the water table need to be considered to correctly simulate transport in the subsurface at the transition of the unsaturated–saturated zone. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
17.
18.
Flow and transport simulation in karst aquifers remains a significant challenge for the ground water modeling community. Darcy's law–based models cannot simulate the inertial flows characteristic of many karst aquifers. Eddies in these flows can strongly affect solute transport. The simple two-region conduit/matrix paradigm is inadequate for many purposes because it considers only a capacitance rather than a physical domain. Relatively new lattice Boltzmann methods (LBMs) are capable of solving inertial flows and associated solute transport in geometrically complex domains involving karst conduits and heterogeneous matrix rock. LBMs for flow and transport in heterogeneous porous media, which are needed to make the models applicable to large-scale problems, are still under development. Here we explore aspects of these future LBMs, present simple examples illustrating some of the processes that can be simulated, and compare the results with available analytical solutions. Simulations are contrived to mimic simple capacitance-based two-region models involving conduit (mobile) and matrix (immobile) regions and are compared against the analytical solution. There is a high correlation between LBM simulations and the analytical solution for two different mobile region fractions. In more realistic conduit/matrix simulation, the breakthrough curve showed classic features and the two-region model fit slightly better than the advection-dispersion equation (ADE). An LBM-based anisotropic dispersion solver is applied to simulate breakthrough curves from a heterogeneous porous medium, which fit the ADE solution. Finally, breakthrough from a karst-like system consisting of a conduit with inertial regime flow in a heterogeneous aquifer is compared with the advection-dispersion and two-region analytical solutions. 相似文献
19.
In the deep Earth, hydrogen mainly occurs as structural hydroxyl and molecular water in minerals and melts, constituting mobile and immobile aqueous components. Hydrous minerals contain hydrogen which occupies a specific structural position and constitutes an indispensable component of chemical formulae. On the other hand, nominally anhydrous minerals do not contain hydrogen in their chemical formulae, but can host trace amounts of water in structural position and lattice defect. The molecular water may occur in the lattice defect as fluid/melt inclusions in minerals. Even though the water content of nominally anhydrous minerals is very limited generally in the order of ppm (parts per million), they may play a significant role in influencing the physicochemical properties of mineral and rock systems. With the continuous improvement of modern instrumentations, the analytical methodology exhibits trends for higher spatial resolution, lower detection limit and integral multiple methods on the water amount and its isotopic ratio. Among these methods, Fourier transform infrared spectrometry remains the most widely used, while secondary ion mass spectrometry, continuous flow mass spectrometry, elastic recoil detection analysis and Raman spectrometry are promising. This paper provides a brief review on the methodological progress and their applications to the analysis of structural water in nominally anhydrous minerals. 相似文献