Potential of multispectral reflectance for assessment of snow geophysical parameters in Solang valley in the lower Indian Himalayas

ABSTRACT

Snow geophysical parameters such as wetness, density and permittivity are a significant input in hydrological models and water resource management. In this paper, we utilize the triangle method based on a feature space developed with the near-infrared (NIR) reflectance and the Normalized Differenced Snow Index (NDSI) for the estimation of surface snow wetness, permittivity and density. The triangular feature space based on NIR reflectance and NDSI is parameterized to yield a linear relationship between the snow wetness and the NIR reflectance. Snow density and permittivity are derived based on the least squares solution of empirical relations based on the observations of surface snow wetness. The proposed methodology was evaluated using Sentinel-2 data, and the modeled snow geophysical parameters were validated with respect to field measurements. Based on the results, it was inferred that the NIR reflectance varies linearly with the liquid water content in the snow. A good agreement was determined between the modeled and measured parameters for wet snow conditions as observed by the coefficient of determination of 0.968, 0.521 and 0.969 for the snow wetness, density and permittivity (real part), respectively. The proposed approach can be significantly utilized with unmanned aerial sensors for monitoring of physical properties of fresh or wet snow and is thus expected to contribute considerably in hydrological applications and avalanche studies.     

Factors affecting the complex permittivity spectrum of soil at a low frequency range of 1 kHz–10 MHz

To establish the factors affecting the permittivity spectrum of soil in the low frequency range, the complex permittivities of soils were measured at the frequency range of 1 kHz–10 MHz. The effects of frequency, water content, soil types and heavy metal contamination on the dielectric response were evaluated and their theoretical mechanisms were discussed. Measurement distortions such as electrode polarization in the low frequency measurements were identified. The permittivity of the soil was analyzed at frequencies above 100 kHz, which was experimentally determined to be the limiting lower frequency. The real permittivities of the soils were strongly related to the volumetric water content, since it is determined by the polarizability of the free water. The effective imaginary permittivities of soils increased with volumetric water content due to the increase in conduction losses. The spatial polarization and conduction loss were found to be the main mechanism in the real and effective imaginary permittivity, respectively. Since such mechanisms are influenced by the specific surface area of the soil particles, the presence of particles with high specific surface area in the soil matrix was found to affect the permittivity of soil. Contamination of saturated soil by cationic species resulted in decreases in the real permittivity due to the decreased orientation polarization of water molecules caused by hydration of ions, but increases in the effective imaginary permittivity due to ionic conduction.     

基于速度分析的探地雷达阻抗介电常数反演

阻抗反演是利用波阻抗与介电常数关系开展地下介质参数估计的重要技术,在探地雷达以及叠后地震资料解释中具有广泛的应用。常规阻抗反演需要钻孔或测井曲线作为约束项,约束项信息直接影响阻抗反演的估计精度。在缺少钻孔数据的实际应用中,如何开展探地雷达阻抗反演是该方法研究的重要内容之一。基于上述问题,本文提出了基于速度分析的探地雷达阻抗反演方法。其基本思想是基于多偏移距雷达数据开展速度谱分析和Dix反演,以获得不同深度的速度信息作为阻抗反演的约束项;同时,采用K-means方法自动拾取速度谱信息,大大降低了常规人工拾取误差,提高了计算效率。通过典型随机土壤介质模型,验证了本文方法在无钻孔条件下仍然可以获得较好的介电常数估计结果,并测试噪声适应能力强。最后通过美国密歇根州Wurtsmith AFB,in Oscoda区域的探地雷达数据测试了本文提出方法在探地雷达实测数据参数估计中具有较好的应用效果。     

A strategy for the determination of the dielectric permittivity of a lossy soil exploiting GPR surface measurements and a cooperative target

In this paper we deal with an indirect measure of the dielectric permittivity of the soil starting from GPR surface data collected on a buried “cooperative” target, meant as an object buried on purpose and whose extent is known a-priori. This target is exploited in order to achieve, from its image obtained from a suitable GPR data processing, an indirect measure of the dielectric permittivity of the embedding soil. GPR data processing is based on a linear microwave tomographic approach funded on the Born Approximation. Using this Born approach on two-dimensional inversion tests, we investigate the effect of the soil's electrical conductivity and permittivity on this indirect measure and demonstrate that the electrical field scattered by a spot-like buried object permits an accurate estimation of the soil permittivity even when no information of the soil conductivity is available.     

Measurement of soil water content using ground-penetrating radar: a review of current methods

Soil water content (SWC) is a crucial parameter in ecology, agriculture, hydrology, and engineering studies. Research on non-invasive monitoring of SWC has been a long-lasting topic in these fields. Ground penetrating radar (GPR), a non-destructive geophysical technique, has the advantages of high resolution, deep detection depth, and high efficiency in SWC measurements at medium scale. It has been successfully applied in field investigations. This paper summarizes the recent progress in developing GPR-based SWC measurement methods, including reflected wave, ground wave, surface reflection, borehole GPR, full waveform inversion, average envelope amplitude, and frequency shift methods. The principles, advantages, limitations, and applications of these methods are described in detail. A comprehensive technical framework, which comprises the seven methods, is proposed to understand their principles and applicability. Two key procedures, namely, data acquisition and data processing, are emphasized as crucial to method applications. The suitable methods that will satisfy diverse application demands and field conditions are recommended. Future development, potential applications, and advances in hardware and data processing techniques are also highlighted.     

Dielectric relaxation in oil-bearing clayey rocks

The dielectric properties of the bentonite–oil–salt solution mixtures with different water and oil saturation were experimentally studied in the frequency range of 10 kHz to 4 GHz at 25–60 °C. It has been established that besides the region of the Debye water relaxation, there are two more relaxation regions resulting from the interfacial interaction of the mixture components in this frequency range. To describe the dielectric permittivity and equivalent conductivity of the mixture, a spectroscopic model taking into account the multifrequency relaxation is proposed. The dependence of the model parameters on the water saturation and temperatures of the samples has been determined. The experimental data are compared with the modeling results, and the error of prediction for the dielectric permittivity and conductivity of mixture is estimated using the proposed model.     

格子玻耳兹曼方法计算混合物整体电导率

本文采用格子玻耳兹曼方法计算混合物的整体电导率．整体电导率与各组分的电导率、体积分数和混合物结构有关．数值计算方法的有效性通过两相混合物并联或串联模型的解析解加以验证．对随机分布模型的计算发现格子玻耳兹曼方法得到的电导率落在H S理论边界内．对Al Bi合金整体电导率的数值模拟结果和实验结果非常相近．对饱和水岩石的介电常数的计算与实验结果相比误差较小．格子玻耳兹曼方法为混合物的整体电导率的计算提供了一个有效的途径.     

基于数字岩心的含裂隙储层砂岩介电性质研究

了解储层岩石的介电特性在石油工业的各个方面都有重要的应用.小尺度裂隙是影响岩石介电性质的地质因素之一,获得裂隙对含裂隙岩石介电性质影响的定量关系具有重要的理论和实践意义.以含裂隙人造砂岩的三维微观数字结构为基础,通过基于三维有限差分算法计算的岩石介电性质与实验数据的对比验证数值计算方法的有效性.在此基础上,通过理论模型获得不同孔隙度基质的介电性质,并在不含裂隙人造砂岩的三维微观数字结构中人为添加以裂隙密度和纵横比为定量表征参数的裂隙,应用验证后的数值算法模拟随频率变化的含裂隙砂岩的介电性质,分析和研究不同孔隙度基质中定向排列裂隙对砂岩介电性质的影响.结果表明,当裂隙孔隙度随裂隙纵横比或裂隙密度发生改变时,含裂隙砂岩的介电性质与裂隙密度以及裂隙纵横比呈正相关关系,而当裂隙孔隙度保持不变时,含裂隙砂岩的介电性质随裂隙纵横比的减小而增大;裂隙参数的改变对不同基质孔隙度的含裂隙砂岩的介电性质的影响趋势较为一致,但随着基质孔隙度的减小,裂隙对砂岩介电性质的影响逐渐增大.裂隙参数和基质孔隙度对含裂隙砂岩介电性质影响的研究结果为基于介电特性的裂缝性油气储层的定量表征提供了依据,在油气勘探开发中具有重要的应用前景.     

Time domain reflectometry measurement principles and applications

Time domain reflectometry (TDR) is a highly accurate and automatable method for determination of porous media water content and electrical conductivity. Water content is inferred from the dielectric permittivity of the medium, whereas electrical conductivity is inferred from TDR signal attenuation. Empirical and dielectric mixing models are used to relate water content to measured dielectric permittivity. Clay and organic matter bind substantial amounts of water, such that measured bulk dielectric constant is reduced and the relationship with total water content requires individual calibration. A variety of TDR probe configurations provide users with site‐ and media‐specific options. Advances in TDR technology and in other dielectric methods offer the promise not only for less expensive and more accurate tools for electrical determination of water and solute contents, but also a host of other properties such as specific surface area, and retention properties of porous media. Copyright © 2002 John Wiley & Sons, Ltd.     

Measurement of the Dielectric Properties of Volcanic Scoria and Basalt at 9370 MHz

Dielectric data for volcanic scoria and basalt on the earth at microwave frequency are extremely sparse, and also crucial for volcanic terrains imaging, and development. In consideration of their similarity to lunar regolith (soils and rocks) in chemical and mineral composition, the dielectric data is significative for passive and active microwave remote sensing on the Moon. This study provides the data about the dielectric properties of three kinds of scoria and two kinds of basalt in China. The method put forward in this paper is also applicable for measuring the dielectric properties of dry rocks and other granular ground materials with low complex dielectric constants. Firstly, the authors measured the ε‘ and tanδ values of strip specimens prepared from the mixture of scoria or basalt powder and polythene with the resonant cavity perturbation method at 9370 MHz. Secondly, from the ε‘ and tang values of the mixture, the ε‘s and tanδs values of sofid scoria and basalt were calculated using Lichtenecker‘s mixture formulae. Finally, the effective complex dielectric constants, ε‘e and tanδs, of scoria at different bulk densities were calculated. The results have shown that the ε‘s and tang svalues of all solid basaltic materials measured (both solid basaltic scoria or basalt) are approximately 7 and 0.05,respectively. With increasing bulk density of scoria, the ε‘s and tanδs values of scoria increase significantly.