土壤水盐介电模型对比与分析

土壤介电常数是微波遥感反演土壤水分和盐分的基础,是微波遥感研究的主要参数之一,选用模拟精度较高的土壤水盐介电模型对提高土壤水分和盐分反演精度具有重要意义。目前,土壤介电模型无法定量描述盐分对土壤介电常数的影响。采用Dobson模型及考虑盐分影响的Dobson-S模型、GRMDM模型、HQR模型和WYR模型分别模拟了土壤温度为25℃时不同土壤质地、含水量和含盐量土样在L、C、X波段的复介电常数实部与虚部,并将模拟结果与微波网络分析仪测量值进行对比分析,得到以下结论:(1)Dobson模型和GRMDM模型可较好地实现非盐渍土介电常数实部的模拟,而低频波段虚部的模拟值小于测量值;(2)Dobson-S模型对盐渍土介电常数实部的模拟精度较高,在L、C、X 3个波段相关系数(R)均为0.97,均方根误差(RMSE)小于2.10;但对于盐渍土介电常数虚部,在土壤体积含水量不同的情况下,Dobson-S模型、HQR模型和WYR模型的模拟精度不同。研究结果对选取适当的土壤介电模型反演土壤水分和盐分具有一定的参考价值。     

含水含盐土壤的微波介电特性分析研究

用微波网络分析仪测量了实验室制备的各种不同含水量,含盐量的土壤样品的复介电常数,研究了介电常数的实部和虚部与频率、盐度、含水量的关系,得出结论：频率、盐度对土壤介电常数的实部的影响很小,对于某一特定土壤,其介电常数的实部有土壤的含量决定;在较低频率范围内（f＜2GHz),虚部随着的频率增大而迅速下降,高频部分则趋向于一定值,当土壤潮湿含水时,实验结果表明,波长较长的波段,如P波段或L以段对土壤含盐程度具有更高的敏感性,其含盐量对虚部在较低频范围（f＜5GHz)影响很大;这为利用微波遥感进行土壤盐碱化程度监测,提供了可能和实验依据。     

吉林西部盐碱地特性微波双频差分无损探测

针对吉林西部盐碱地特性(内地苏打盐类型),应用车载双频段被动微波遥感系统,对不同盐碱状态的4个裸盐碱区进行双极化多角度微波辐射无损探测。基于多角度双频率双极化的观测数据优势,选择逼近式迭代算法来反演其介电常数虚部,Dobson模型反演介电常数实部。在此基础上,应用双频差分法研究了该区域盐碱地介电特性与含水量、含盐量的关系。双频差分结果表明:实部双频差分与盐碱土含水量呈线性关系,相关系数为0.9996;虚部双频差分与含盐量呈线性关系,相关系数为0.9977。这为应用被动微波遥感定量反演盐碱地特性(含水量、含盐量)奠定了理论基础。     

无创血糖检测中不同葡萄糖浓度的介电- 频率响应特性研究

无创血糖检测技术具有无痛感、不易感染和可连续监测等优点,是血糖检测技术发展的重要 方向。为了研究在不同频率下、不同葡萄糖浓度对介电特性的影响,该文首先以不同葡萄糖浓度的 水溶液为研究对象,探索了 500 kHz～5 MHz 频率范围内不同葡萄糖浓度水溶液的介电-频率特性。 研究表明,葡萄糖水溶液在 500 kHz～5 MHz 的响应特性与高频下的响应特性不同。在该频段下,当 葡萄糖浓度不变时,水溶液的复介电常数的实部和虚部随着频率的增大而减小;当频率不变时,水 溶液的复介电常数的实部和虚部随着葡萄糖浓度的增大而减小。其次,该文还通过对复介电常数测量 值进行二阶 Debye 模型拟合,并对 Debye 模型中的参数进行了二次多项式拟合。拟合的决定系数均 高于 0.93,最终得出了葡萄糖浓度为 0～16% 水溶液的复介电常数在不同葡萄糖浓度和频率下的相关 函数,量化了葡萄糖水溶液的复介电常数与葡萄糖浓度及频率的关系。最后,通过建立包含皮肤、血 液、肌肉的无创血糖检测模型,并采用基于时域有限差分法对模型进行仿真分析。结果表明,接收电 极 2 与 3 之间的电压差值随着葡萄糖浓度的增加而线性增大,为基于 500 kHz～5 MHz 频率范围内的 无创血糖检测提供了一定的理论基础。     

基于FDR技术的土壤水分传感器设计

本文以土壤的介电理论为基础,通过测量土壤的介电常数随土壤水分变化的规律得知土壤的体积含水量,并利用土壤水分频域反射法实现土壤水分的测量.此方法可以连续检测土壤含水量的变化,较好的反映土壤水分的变化趋势.本文所设计的土壤水分传感器因具有多个测量分探头,因此可测量较深的土壤.因采用RS485总线通信,使传感器具有实时测量、...     

合成孔径雷达遥感原理及应用（四）

６ＳＡＲ应用简介概括地说，合成孔径雷达影像主要反映了如下几方面的地表特性：（１）从介电性质方面看，主要是含水量的问题。水是地球上普遍存在的物质，自由水在微波波段的介电常数，不论实部还是虚部都非常大。束缚水的介电常数尽管比自由水要小些，仍比较大，与其它...     

不同介电常数模型的平静海表面亮温仿真差异性分析

利用介电常数模型仿真平静海表面亮温是海洋盐度遥感反演的基础工作之一。利用Matlab软件对K-S模型、M-W模型和Bl模型3种介电常数模型进行了仿真。首先分析了3种介电常数的实部和虚部值随电磁波入射角变化的差异性,然后通过介电常数模型获得的3种平静海表面亮温,分析了在盐度为30～40psu以及不同入射角的情况下,3种介电常数模型得到的平静海表面亮温和盐度变化率的关系。研究结果表明,在L频段(1.4～1.427GHz),3种模型的差异主要体现在实部,K-S模型介电常数实部值相对于其他2个模型更高,电磁波衰减程度基本一致;在入射角为55°时,亮温与盐度的变化率差异最明显,3种模型的垂直极化亮温的变化率比水平极化亮温高30%左右。     

互补开口谐振环微带传感器介电常数的测量

介电常数是材料的重要特性之一,采用互补开口谐振环微带传感器实现了不同厚度待测物质介电常数的无损测量。方形互补开口谐振环蚀刻在微带线接地平面上,与微带线耦合实现谐振,分析了谐振器的等效电路,讨论了介电常数与谐振频率之间的关系。通过有限元分析,谐振频率的负二次方与待测物质的介电常数实部值存在线性关系,且线性关系受待测物质的厚度影响;介电常数的虚部值对谐振频率的影响可忽略不计;最终建立了介电常数实部值与谐振频率和样本厚度之间的数学解析式。实验测试结果表明,当待测样品的厚度大于2 mm时,实部介电常数的相对测量误差小于3.5%。     

基于高频电容法的耕地土壤水分检测研究

利用土壤的介电特性对土壤的体积含水量进行测量.采用高频电容法作为测量方法,分别对红壤土、潮土、水稻土3种耕地土壤的含水量进行了测量.首先进行测量原理的分析,根据土壤测试极板的等效高频电气模型与固定电感相串联求得测量极板的等效电容值与串联谐振频率的关系.然后经过计算与电路仿真,绘出谐振频率与土壤体积含水量的理论关系曲线.最后通过实验对3种耕地土壤的实际含水量进行了测量,得到了实际测量与理论值的对比图.经过分析测量结果,证明实际测量结果符合理论推算,具有实际应用的价值.     

基于有限元法的材料电特性计算机仿真研究

等效电特性(如介电常数和电导率)是复合材料的重要物理属性,通常受到材料成分、占比、几何结构等多种因素影响。为深入研究夹杂物形状对复合材料等效电特性的影响机理,采用有限元法(FEM)模拟分析了具有不同形状夹杂物的复合材料模型在静电场下所表现出的等效介电特性,并提出以模型内部所产生的平均场浓度和场波动参数来观察并解释夹杂物几何结构对等效电特性的影响规律。论文借助计算机仿真技术,计算了复合材料模型中,当夹杂物和宿主的介电常数比值不同时,夹杂物几何结构对材料等效介电常数的影响,并将仿真结果与几种经典混合模型的解析公式进行了比较。分析结果表明,复合材料的内部平均场强及场波动变化与等效介电常数变化规律相吻合,而场波动与夹杂物几何结构特征有较为直接的相关性,从而可对材料等效电特性的变化进行合理解释。这一模拟分析方法可为复合材料设计等应用研究提供理论参考依据。     

Dielectric Properties of Saline Soil and an Improved Dielectric Model

The measurement and analysis of the dielectric constant of soil samples with different moisture and salinity are achieved based control experiment. The saturation is introduced to the dielectric model of salinity soil to improve simulation accuracy by taking the Stogryn model and the influence of soil solution ion concentration, conductivity, moisture content, and salt content for dielectric constant imaginary part into consideration. The results indicate that the soil salt content has little influence on both real part and imaginary part of dielectric constant when soil volumetric moisture content is low, while soil volumetric moisture content is high, the real part of the dielectric constant decreases with the increase of soil salt content, and the imaginary part of the dielectric constant increases. The improved dielectric model of salinity soil can well reveal the changes of dielectric constant, and it is also having a great effect in Baiyin soil samples. That is to say, the improved dielectric model can apply to different soil types.     

Dielectric properties of salt-affected soils

A detailed laboratory experiment was conducted on three soils of different textures viz., sand, sandy clay loam and clay to study the influence of soil salinity and sodicity on the complex dielectric behaviour of soils as a function of volumetric soil moisture using an L-band (1 ·25 GHz) dielectric probe. The results revealed that soil salinity has no influence on the real part of the dielectric constant (?') whereas, the imaginary part (?'') is dependent and increases with increase in salinity for all the soils considered. It was found that the real part is more dependent on soil moisture and imaginary part on soil salinity. The sodicity of a soil has no influence either on real part or imaginary part. This study shows L-band (1·25 GHz) microwave response to soil salinity. It also demonstrates the possibility of separating saline soils from sodic soils at L-band frequencies under moist soil conditions.     

Comparative Analysis of Soil Water and Salt Dielectric Model

The soil dielectric constant，the basis of the microwave remote sensing inversion of soil water and salt，is one of the main parameters of microwave remote sensing research.It is very important to select the high precision soil water and salt dielectric model to improve the precision of soil water and salt inversion.However，the existing soil water and salt model still can’t quantitatively describe the effect of salt factor on soil permittivity.This paper simulates the complex permittivity of different texture，water content and salinity wet soil by Dobson model，Dobson\|S model，GRMDM model，HQR model and WYR model at L，Cand X bands when soil temperature equal 25 ℃.Comparison and analysis the simulation values with measured values by microwave vector network analyzer.The results show：(1)Dobson model and GRMDM model can accurately simulate the real part of dielectric constant of non\|saline soil，while the stimulated values of imaginary part is less than the measured values;(2)Dobson\|S model can well simulate the real part of the dielectric constant of saline soil，at L，C\nd Xbands the correlation coefficient R equal 0.97，the RMSE is less than 2.10.But for the imaginary part of the dielectric constant of saline soil，the Dobson\|S model，HQR model and WYR model with different simulation accuracy，when soil water content different.This study would benefit the choice of a suitable soil dielectric model for soil moisture and salinity retrieval.     

Modified Alex–Behari model for soil moisture as a function of salinity,texture and frequency

Alex and Behari obtained experimental soil moisture data at microwave frequencies and computed emissivity from these. Following this they suggested an empirical model which provides a good agreement up to a soil moisture value of 25%. Taking into consideration the soil texture, the modified Alex–Behari (MAB) model provides agreement with the available data up to 40%. A non-linear relationship between volumetric soil moisture and emissivity is obtained. The dielectric constant shows an increase with volumetric soil moisture. The dielectric properties of the soil are known to depend on soil moisture content along with other factors like salinity, texture and frequency. In the present investigations the experimental dielectric constant of various types of soils was taken in the frequency range (1.4–18.0 GHz) to fit the modified model in the given range of moisture content. The computed data show that the real part of the dielectric constant decreases and imaginary part increases with soil salinity. It is suggested that the proposed model will be of interest to agricultural scientists, and applicable to remote sensing of salt-affected areas.     

基于地基微波辐射计数据评估不同土壤介电模型反演土壤湿度的适用性

以青藏高原开展的L波段地基微波辐射（ELBARA-III型）综合观测试验为依据,基于 \tau - \omega 辐射传输模型评估了Wang-Schmugge、Mironov、Dobson和 Four-Phase 4种土壤介电模型对L波段微波亮温模拟及土壤湿度反演的影响。结果表明：相同植被和粗糙度参数化方案条件下,4种土壤介电模型对微波亮温模拟存在明显差异,当土壤湿度小于0.23 m3·m^-3时,Wang-Schmugge模型与其他3种土壤介电模型微波亮温模拟结果差异最为显著,水平和垂直极化微波亮温模拟最大差值可达8.0 K和4.4 K;当模拟土壤湿度大于0.23 m3·m^-3时,Four-phase模型模拟的微波亮温显著高于其他3种土壤介电模型模拟结果;当土壤湿度饱和时,4种土壤介电模型间水平和垂直极化微波亮温模拟最大差值约为6.1 K和4.8 K,且4种土壤介电模型对水平极化微波亮温模拟的差异比垂直极化模拟的差异更为显著。而基于4种介电模型的土壤湿度反演对比试验表明,水平极化条件下基于Wang-Schmugge模型反演土壤湿度,较其他参数化方案,能有效减轻反演土壤湿度对观测土壤湿度的低估,Mironov模型减轻了垂直极化条件下反演土壤湿度对观测值的高估程度。在现有 \tau - \omega 模型参数化方案的基础上,总结了4种土壤介电模型在青藏高原典型草地下垫面的适用性,将为星载L波段辐射计青藏高原土壤湿度反演应用提供客观的土壤介电模型方案选取依据。     

Evaluation of the Applicability of Different Dielectric Models for Soil Moisture Retrieval based on the Ground-based Radiometer Measurements

Based on soil moisture and freeze/thaw comprehensive experiments conducted at the north-eastern part of the Tibetan Plateau, the L-band brightness temperature, the in-situ soil moisture and temperature, vegetation leaf area index are measured simultaneously for the purpose of evaluating performances on forward brightness temperature simulation and soil moisture retrieval using four dielectric constant models, including Wang-Schmugge, Mironov, Dobson, and Four-Phase model. The forward brightness temperature simulations indicate that the difference of simulated brightness temperature between Wang schmugge model and the other three dielectric constant models is most significant at lower soil moisture content condition (soil moisture is less than 0.23 m3·m^-3) , nevertheless, the difference of Mironov model simulation is most significant in contrast with the ones of other three models at higher soil moisture condition (soil moisture is greater than 0.23 m3·m^-3). The practical retrieval of soil moisture from the ground-based radiometer measurements indicate that Wang-Schmugge model can effectively reduce the underestimation of soil moisture at the horizontal polarization, this resulted an improvement to the accuracy of retrieved soil moisture. Mironov model can reduce the underestimation of retrieved soil moisture at the vertical polarization. In accordance with a state-of-the-art parameterization scheme, the evaluation of performances of four dielectric constant models at the typical alpine meadow is potential for selecting optimum soil moisture retrieval by using soil dielectric model from space-borne L-band radiometer observation over the Tibetan Plateau     

介电溶液测试土壤水分传感器性能的实证研究

利用土壤等效介电溶液代替土壤测试与评估土壤水分传感器的性能,具有便捷、快速的优点。为验证传感器在介电溶液中的测试结果是否与实际土壤中一致,利用去离子水和2—异丙氧基乙醇(2-isoproxyethanol)或二氧六环(dioxane)2种溶液混合,配制了一系列等效土壤体积含水率为0.9%~51.8%的待测介电溶液,同时取广州地区的典型红壤和雷州半岛的典型砖红壤,配制一系列与介电溶液等效含水率相对应的土样,分别从电气特性、与土壤含水率的函数关系、温度变异性和稳定性4个方面测试传感器的性能,并将介电溶液中的测试结果与2种土样中比较。实验结果表明:介电溶液中的测试结果与红壤和砖红壤中基本上一致,介电溶液在某种程度上可以代替土样进行土壤水分传感器的性能测试。     

GA-PLS方法提取土壤水盐光谱特征的精度分析

光谱定量遥感已成为土壤盐渍化大尺度调查的有效手段之一,但黄河三角洲地区盐渍化土壤的光谱响应特征尚未明确。以黄河三角洲野外测定土壤体积含水率、电导率为例,应用遗传偏最小二乘法(GA-PLS)在小样本集条件下提取盐渍土壤的水分-盐分的光谱响应特征,利用蒙特卡罗方法随机模拟结果表明:在不同土壤水盐含量条件下,GA-PLS方法所提取的光谱特征具有鲁棒性,含水率模型稳定在23个波段变量,即响应特征为365~425,500~515,720~740,755~765与955~965 nm;土壤电导率模型的特征集数目为20个波段变量,特征为370~385,405~425\,500~535,650~660,755~760与1 030~1 050 nm。实验在不同预处理模型下,GA-PLS算法所建立水盐光谱模型较PLSR模型均显示出更高的精度。其中,包络线预处理方法与GA-PLS算法相结合效果最优,其水分光谱模型测试集拟合精度(R²),预测残差平方和(PRSS)与残差预测方差(RPD)分别为0.88,9.36与15.80;土壤光谱模型测试集精度R²,PRSS与RPD分别为0.71,15.68与13.76。