基于分段涂层TDR探针的含水合物多孔介质电学参数测量仿真研究

针对海洋沉积物中天然气水合物饱和度评价需求，提出了基于分段涂层TDR探针的沉积物介电常数和电导率同步测量新方法。针对无涂层探针、全涂层探针以及分段涂层探针分别建立了模拟TDR测量响应的有限元数值模型，仿真研究了涂层参数对介电常数和电导率测量性能的影响规律，继而应用于含水合物多孔介质的测量并对误差进行了分析与校正。研究结果表明：探针涂层的厚度和介电常数直接影响采集电压信号的衰减程度，因此需根据被测介质的电学性质对其进行优化设计；在涂层厚度和介电常数已确定的条件下，通过改变涂层间隙长度可以调节探针所适用的电导率测量范围；当测量非均匀介质时，可以通过增加涂层间隙的个数来提高电导率测量的准确度；采用分段涂层探针测量含水合物多孔介质的介电常数和电导率时，需要对涂层引起的误差进行校正。     

TDR moisture measurements in granular materials: From the siliceous sand test case to the applications for agro-food industrial monitoring

Different approaches are commonly available for the continuous monitoring of moisture and dielectric properties of various materials. In particular Time Domain Reflectometry (TDR) is the standard method for measuring soil water content. Nevertheless, the state of the art is rather lacking in assessing specific calibration procedures allowing the accurate moisture monitoring of granular materials. To fill this gap, the adoption of TDR for such purposes is investigated. Starting from measurements on siliceous sand, an in-depth analysis is extended to various feedstuff materials (such as corn, corn flour and bran). Furthermore, the adopted methodology is fully assessed from a metrological point of view, thus confirming its suitability for the considered applications.     

基于TDR的多孔介质中含水/水合物饱和度测量方法仿真研究

为了优化设计时域反射技术（TDR）中的探针结构,建立基于TDR响应的含水/水合物测量模型,利用有限元数值模拟方法建立了TDR测量过程数值仿真模型。分别以空气、不同浓度氯化钠溶液以及不同水合物含量的石英砂为被测介质验证了模型的正确性、研究了被测介质电导率和介电常数对反射波形的影响规律。通过改变被测介质的介电常数来模拟含水/水合物饱和度不同的石英砂,随着石英砂中水合物含量的增加,含水量逐渐降低,表观介电常数随之减小,电磁波传播速度随之以非线性形式增加;与理论值相比较,仿真计算所得到的传播速度最大误差处于5%以内。下一步需要在数值模型中的被测区域中填充各相异性材料来更加真实地模拟含水合物沉积物被测介质。     

Ground-penetrating radar measurement of crop and surface water content dynamics

Ground-penetrating radar (GPR) with a suspended 1 GHz horn antenna was deployed for measurement of soil water contents and crop canopy properties over bare and electrically terminating surfaces. Surface reflection (SR) and signal propagation times (PT) were used to independently determine dielectric permittivity and water content of soil and canopy. Measured surface reflection coefficients progressively decreased with increasing canopy biomass according to Beer-Lambert type relationships. In contrast, PT measurements remained unaffected by canopy, and hence provided an accurate account of soil water content dynamics. Immediately after canopy removal, SR-based soil water content measurements were in close agreement with PT values. Canopy dielectric properties were inferred from canopy water contents (?_c-CWC) and canopy propagation times (?_c-CPT). Distinct canopy reflections were correlated with key canopy biophysical parameters. The study demonstrates the usefulness of a horn antenna GPR for characterization of vegetation canopy scattering, and for subcanopy water content measurements within a well-defined footprint, thereby offering a potential for calibration and verification of radar data collected from air- and spaceborne platforms.     

基于内部阵列电极的电容层析成像系统

为了研究电容层析成像系统在测量高介电常数流体中的应用,设计了一套具有内部阵列电极的电容层析成像传感器,改善了传统传感器的灵敏度和非线性特性,拓宽了系统的测量范围。用蒸馏水作为连续相介质进行了数据采集和图像重建,并进一步研究了介质电导率对系统成像的影响。实验表明,该系统可以实现高介电常数介质的测量,并且可用来测量具有微弱导电能力的物体。     

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.     

A MATLAB program for estimation of unsaturated hydraulic soil parameters using an infiltrometer technique

We combined an inverse routine for assessing the hydraulic soil parameters of the Campbell/Mualem model with the power series solution developed by Philip for describing one-dimensional vertical infiltration into a homogenous soil. We based the estimation routine on a proposed measurement procedure especially suitable for early-time infiltrometer experiments where the flow can be considered as one-dimensional. The routine requires input of the initial soil water content and cumulative infiltration in two experiments with different pressures at the upper boundary and/or initial conditions. An independent measurement of the soil water content at saturation may reduce the uncertainty of estimated parameters. Response surfaces of the objective function were analysed. Scenarios for various soils and conditions, using numerically generated synthetic cumulative infiltration data with normally distributed errors, show promising results for finding the true values of the optimized parameters. We also investigated the effects of measurement frequency for the cumulative infiltration and errors in water content determinations.     

Errors in soil moisture content estimates induced by uncertainties in the effective soil dielectric constant

Soil moisture content (SMC) is an important variable in the hydrological cycle. Sensors have been developed to enable continuous monitoring of SMC (remote sensing from satellite and devices for in situ measurements), many of which are based on measurement of the soil dielectric properties from which SMC is inferred. Most SMC estimation techniques depend on the relationship between SMC and its dielectric properties, but the lack of a universal effective soil dielectric model introduces an additional source of error on SMC estimates. This work compares nine models of this relationship, and quantifies errors due to uncertainties in the relation between water content and dielectric properties. Errors of around 4% are reported with maximum figures at relatively low water content. Inconsistency between these models and the inconsistency in the effect of soil texture on SMC retrieval from satellite‐based sensors is also evaluated.     

Utilizing calibrated GPS reflected signals to estimate soil reflectivity and dielectric constant: Results from SMEX02

Extensive reflected GPS data was collected using a GPS reflectometer installed on an HC130 aircraft during the Soil Moisture Experiment 2002 (SMEX02) near Ames, Iowa. At the same time, widespread surface truth data was acquired in the form of point soil moisture profiles, areal sampling of near-surface soil moisture, total green biomass and precipitation history, among others. Previously, there have been no reported efforts to calibrate reflected GPS data sets acquired over land. This paper reports the results of two approaches to calibration of the data that yield consistent results. It is shown that estimating the strength of the reflected signals by either (1) assuming an approximately specular surface reflection or (2) inferring the surface slope probability density and associated normalization constants give essentially the same results for the conditions encountered in SMEX02. The corrected data is converted to surface reflectivity and then to dielectric constant as a test of the calibration approaches. Utilizing the extensive in-situ soil moisture related data this paper also presents the results of comparing the GPS-inferred relative dielectric constant with the Wang-Schmugge model frequently used to relate volume moisture content to dielectric constant. It is shown that the calibrated GPS reflectivity estimates follow the expected dependence of permittivity with volume moisture, but with the following qualification: The soil moisture value governing the reflectivity appears to come from only the top 1-2 cm of soil, a result consistent with results found for other microwave techniques operating at L-band. Nevertheless, the experimentally derived dielectric constant is generally lower than predicted. Possible explanations are presented to explain this result.     

A dielectric-based combined horizontal sensor for on-the-go measurement of soil water content and mechanical resistance

Precision agriculture is drawing widespread attention and increasing interest in the use of on-the-go sensors to extract soil and plant information. This new trend is evident from an increased number of (tillage) studies concerning the development of sensors for measuring physical soil properties. In this study, a new dielectric-based horizontal sensor was designed and stationary calibrated in pots for measurement of volumetric soil water content. Subsequently, the sensor was combined with a load cell and installed on a tine with thickness of 25 mm, and its dynamic performance was assessed. The load cell behind the tine measures horizontal soil mechanical resistance. In order to evaluate the on-the-go performance of this combined sensor, two experiments were carried out in a soil bin, with the purpose of (i) measuring soil water content along a transect of longitudinally variable water contents, (ii) investigating the difference in horizontal resistance force measured by either the combined (horizontal force and water content) or a single sensor (horizontal force only). The stationary calibration results showed that quadratic equations with coefficients of determination (R²) of 0.989 and 0.918 could be fitted to the data points obtained from measurements in soil bulk densities of 1.5 and 1.2 g cm⁻³, respectively. The results of the soil bin experiments indicated that the response of the dielectric sensor to soil water content variations was reasonable, but that the output voltage of the sensor should be amplified for a better sensitivity and resolution. The presented combined sensor can provide useful information on soil physical properties towards site specific applications in soils.     

基于信号波形幅度检测放大技术的电容式土壤水分传感器研究

土壤水分量测对于农田系统的评估和选择、水资源的合理利用是十分重要的。本文根据土壤水分与土壤相对介电常数的关系,基于信号波形幅度检测放大技术设计了一种电容式土壤水分传感器。在标准溶液样品、粘壤土、砂壤土、粘土土样中对本文提出的传感器进行测试。实验结果显示,传感器输出电压与被测介质含水量有良好的线性关系（R2=0.81~0.99）,传感器灵敏度受土质影响明显,实际应用中时需要根据土质进行校准,传感器功耗低,在2.5V供电电压下功耗低于8mW。本文设计的传感器可推广至精准农业系统应用中。     

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。     

电容式冻土测量传感器设计

冻土与未冻土中的介电常数和温度物理参数有一定的差异,且差异在数值上较明显。基于这一特性,提出了利用空气、固态土、水和冰物理特性存在差异的原理检测冻土的方法,设计了一种电容式冻土测量传感器,实现了土壤水分、地温及冻土深度多参数融合测量。通过与人工测量的冻土深度进行对比分析,结果表明:其相关系数达到了0.99,平均绝对误差小于2.5 cm,满足冻土自动测量技术要求,可应用于冻土观测站,代替人工观测。     

Sensitivity of near infrared total water vapour estimate to calibration errors

Analysis of satellite data to estimate the precipitable water (also called the columnar water vapour) amount often leads to systematic errors in deduced precipitable water (PW). The causes of systematic errors are likely to be instrumental calibration errors rather than variability of atmospheric parameters. We use the MODTRAN 4.0 radiative transfer code to model effects of various calibration errors on the Multi-spectral Thermal Imager (MTI) daytime total water vapour estimate. From the considered sources of calibration errors (spectral band centre error, spectral bandwidth error and radiometric calibration error) the radiometric calibration error has the largest influence on the accuracy of total water vapour estimate. When the radiometric calibration error between 1% and 5% is combined with the estimated spectral band centre error of 1 nm and the bandwidth error of 0.5 nm, the total systematic error of the columnar water vapour estimate is expected to be between 8% and 26%. The accuracy of the retrieved PW using the MTI imagery over the NASA Stennis site and Oklahoma DOE (Department of Energy) ARM (Atmospheric Radiation Measurement program) site is about 17%, well within the estimated range due to calibration errors. A similarity between the MTI and the MODIS (Moderate Resolution Imaging Spectral-Radiometer) bands used for water vapour estimate suggests that a similar error analysis may be valid for the MODIS sensor. However, the narrow band instruments (with bandwidth around 10 nm) are much more sensitive to the band centre calibration error.     

基于机器学习的非接触式水位计校准算法研究

由于环境等因素影响,用于测量水位的超声波、雷达式等非接触式水位计存在一定的测量误差,更换高精度设备会增加成本,为解决测量误差,提出基于机器学习的水位计校准算法。该算法融合测量误差产生的环境因素,采用迭代 Boosting 学习算法,构建 Adaboost 的单层决策树模型,采用误差辗转递送的强学习算法对测量误差进行校准。算法仿真结果显示,校准结果可以很好地拟合标准设备测量值,校准算法不仅克服更换设备带来的成本,还将传统的仪器校准迁移至后端软件层面,为解决非接触式水位计校准提供新手段。     

On the complexity of energy efficient pairwise calibration in embedded sensors

Technological advances in nanotechnology enabled the use of microelectromechanical systems (MEMS) in various application areas. With the integration of various sensor devices into MEMS, autonomously calibrating these sensors become a major research problem. When performing calibration on real-world embedded sensor network deployments, random errors due to internal and external factors alter the calibration parameters and eventually effect the calibration quality in a negative way. Therefore, during autonomous calibration, calibration paths which has low cost and low error values are preferable. To tackle the calibration problem on embedded wireless sensor networks, we present an energy efficient and minimum error calibration model, and also prove that due to random errors the problem turns into an NP-complete problem. To the best of our knowledge this is the first time a formal proof is presented on the complexity of an iterative calibration based problem when random errors are present in the measurements. We also conducted heuristic tests using genetic algorithm to solve the optimization version of the problem, on various graphs. The NP-completeness result also reveals that more research is needed to examine the complexity of calibration in a more general framework in real-world sensor network deployments.     

A verification of the 'triangle' method for obtaining surface soil water content and energy fluxes from remote measurements of the Normalized Difference Vegetation Index (NDVI) and surface e

An inversion procedure is presented for estimating surface soil water content (as surface moisture availability, Mo ), fractional vegetation cover ( Fr ), and the instantaneous surface energy fluxes, using remote multispectral measurements made from an aircraft. The remotely derived values of these fluxes and the soil water content are compared with field measurements from two intensive field measurement programs FIFE and MONSOON '90. The measurements from the NS001 multispectral radiometer were reduced to fractional vegetation cover, surface soil water content (surface moisture availability), and turbulent energy fluxes, with the application of a soil vegetation atmosphere transfer (SVAT) model. A further step in the inversion process involved 'stretching' the SVAT results between pre-determined boundaries of the distribution of normalized difference vegetation index (NDVI) and surface radiant temperature ( To ). Comparisons with measurements at a number of sites from two field experiments show standard errors, between derived and measured fluxes, generally between 25 and 55Wm-2, or about 10-30 per cent of the magnitude of the fluxes and for surface moisture availability of 16 per cent.     

便携式土壤水分测试系统设计

土壤水分含量不仅对农作物生长有较大的影响,而且对越野车辆地面通过性也有重要的影响.设计了一种基于时域反射法的土壤含水量测试系统.通过直接数字频率合成器(DDS)产生电磁波测试其介电常数;然后利用介电常数-含水量经验模型得出土壤含水量.系统还配备了GPS接收系统,能记录每次测量的经纬度坐标,并且根据经纬度地名对照表在记录中存储相应的地名.系统通过扩展存储容量使测试记录数可达上万条,并且能通过串口把数据上传到计算机中进行进一步处理.该测试系统具有便携、快速、原位测量的特点,便于构建时空尺度的土壤含水量演变立体分布图,为车辆地面通过性判断提高依据.     

同轴电缆形变TDR监测技术的研究与实现

针对时间域反射测试技术在地质灾害防治、山体滑坡预警,以及土壤水含量分析等诸多领域的应用,使用TDR技术构建的同轴电缆形变监测算法,设计了TDR检测系统硬件电路;运用等效采样算法,实现了高速回波信号的等效采样与重构;通过向同轴电缆施加窄脉冲激励信号,依据回波信号模式分析完成了同轴电缆形变的有效监测;实验室中的大量实验数据表明,将TDR技术应用于同轴电缆形变监测原理正确,文中设计的方案可行.     

基于随机采样的快速非局域均值图像去噪算法

在图像去噪的过程中,针对非局域均值滤波(NLM,non-local mean)去噪方法中存在的运算效率低下问题,提出了一种改进的快速去噪算法.首先,基于蒙特卡罗重要性采样思想,采用Metropolis方法在搜索窗口中对图像的像素点进行随机采样,取代NLM算法在搜索窗口中逐一像素遍历进行加权平均的方法,从而实现了加速.其次,算法在实现加速的过程中一般会影响去噪效果,为了仍保持较好的去噪效果,提出一种改进的权重函数.最后,进行了对比实验,对实验结果从峰值信噪比、运行时间及与原无噪声图像的相似度三个方面进行分析,结果表明,本方法在保持较高信噪比的基础上,处理时间只有标准NLM算法的1/3左右.