土壤含水量检测系统的设计

根据遥感基础理论和数字图像处理法分析了土壤图像灰度值与土壤含水量的非线性关系,设计了土壤含水量检测系统。采用CCD摄像头、控制平台以及电脑和图像采集卡,成功采集到土壤的图像信息,传输给电脑。再通过程序的编写和调试,完成对土壤图像的处理和特征提取,并利用BP神经网络对土壤含水量检测结果进行分析。实验表明BP神经网络建模速度快,检测结果有较高的精度,可以很好的应用于实践。     

沥青混合料含水量集成检测系统设计与研究

为提高路面沥青混合料含水量测量装置精度,简化结构,提出一种1.5 GHz微带环结构的含水量传感器检测系统.因含水量不同,不饱和混合料介电常数变化,导致微带环有效介电常数发生改变,谐振频率偏移.通过谐振频率反演混合料介电常数,建立含水量与有效介电常数的线性关系求得沥青混合料含水量.研究工作包括算法分析、微带环结构设计仿真、系统软硬件集成设计.混合料样本(含水量0 ～ 30％)测试显示测量分辨率≤0.1％,误差≤1％,系统响应时间≤100 ns.这种新型传感器体积小、功耗低、精度高,适合路面测量.     

基于驻波比原理的鲜玉米含水量快速检测方法研究

以鲜玉米为研究对象,研究了一种基于驻波比原理的玉米含水量快速测量方法,该方法采用100 MHz正弦波作为测试信号,长10 mm,直径0.7 mm,间距8 mm的平行双针探头,传输线长37 cm。将重复实验测得的电压差与该组对应的玉米实际水分做拟合,得到较好的线性曲线,其相关系数为0.9062,非线性误差为±1.519%,再对所得的线性模型的稳定性做进一步的实验验证。结果表明:该线性模型的平均误差为-1.15%,最大误差不超过±3%。由此得出,线性度和误差均在合理范围之内,说明利用驻波比法快速检测玉米含水量的方法是可行的。     

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。     

原煤含水量微波加热在线检测方法研究

原煤含水量采用常规测试方法由于耗时长(3H),无法满足火电生产工艺要求,本文提出的采用微波加热及结合抽真空和提高脱水温度的快速失重法,可将测试时间缩短到50秒以内,测试结果与常规测试方法无显著差异;在此基础上本文设计了一套完整的原煤含水量在线测试系统,具有操作方便、快速、与集散控制系统接口方便等优点,结果也较为准确.     

土壤含水量测定方法研究进展

综述了国内外近20a来测定土壤含水量的研究情况,总结了国内外常用的测定土壤含水量的方法及其原理, 比较分析了各种测定方法的优缺点,介绍了一些新兴的土壤含水量测试技术,提出了本领域中存在的主要问题及研究展望,指出未来的土壤含水量测定方法应当是朝着高精度、低成本、非破坏、自动化等方向发展。     

单侧敏感土壤水分传感器设计及标定研究

针对目前土壤水分传感器测量需侵入土壤,无法获取土壤表层含水量信息及其标定过程繁琐等不足,改进ECH₂O传感器探头结构,提出单侧敏感型电容式土壤水分传感器。采用ANSYS软件仿真分析探头灵敏度、敏感深度与探头极宽与极距之比(a/b)的变化关系,认为a/b在0.8～1之间取值时探头特性较优;基于谐振原理设计了带有频伏转化功能的电容测量电路;推导出混合介电参数标定β模型,提出β模型两点标定法。在土壤、泥炭、珍珠岩、醋糟中的试验数据表明：β模型较好地表征了输出电压信号与土壤含水量之间的关系,最小相关系数R²=0.955 4;除珍珠岩外,基于两点标定β模型的测量误差小于0.025;泥炭、醋糟容重变化引起的测量误差小于0.025。     

岩石含水量矩形微带环检测系统的应用研究

针对传统岩石含水量检测设备精度不高、实时性差、结构复杂的问题,设计一种1.5 GHz矩形微带环检测系统,测量原理采用微扰法,当微带环紧贴岩石表面,因为岩石含水量不同,微带环周围电场分布改变,矩形微带环产生不同的谐振频率,通过测量谐振频率和p值可以求得等效介电常数,进而求出岩石含水量。研究工作包括算法分析、结构仿真、样本测试。岩石样本测试结果显示分辨率大于0.1%,误差小于0.6%,系统响应时间小于80 ns,测量精度达到要求。这种新型矩形微带环精度高、结构简单.适合岩石含水量检测。     

西峰黄土高原土壤含水量干旱指数

某时段的干旱不但与同期降水有关,还与前期降水有密切的关系,土壤水分是表达干旱的重要因子,可以综合反映干旱的变化,为此,利用1989～2004年西峰农业气象试验站的土壤水分、降水资料,分析了降水量随时间的变化,0～100cm土壤水分的垂直分布特征和时间变化规律,对春季、伏期、秋季、初春、春末初夏旱土壤含水量与降水量进行了对比分析,并制定了这几个时段的针对土壤含水量的土壤干旱指标。     

同面散射场电容式砂含水量传感器的研究

针对电容式砂含水量传感器的特殊结构,本文从同面散射场电容传感器的等效电容的分析出发,优化了电容极板的大小;使用有限元法分析了极板间距、极板对数以及极板结构对传感器灵敏度的影响;并对传感器的隔离板材料的介电常数选择问题进行了探讨。结果表明双电极小极板结构的普通陶瓷隔离的传感器结构尺寸小,灵敏度高。本研究对同面散射场电容式砂含水量传感器的结构参数优化有实际指导意义。     

微波水分测量的研究

为了能快速、准确地检测物料中的水分含量,设计了一种微波水分检测系统。该系统的工作原理是基于微波透射过含水物料后,其功率变化、衰减量等与物料水分含量有关。该系统工作的中心频率是10.5 GHz;对温度变化、物体颜色及所含盐分等不敏感;水分测量范围可达5%~30%;测量精度为±1%;微波发射功率为10mW。该系统适合检测纸板、布等有一定厚度物料中的水分含量。     

Technical note Remote sensing of soil moisture content over bare soil at microwave frequencies

Abstract

Results of radiometric measurements over bare soil obtained with horizontally polarized microwave radiometers at 1·55 and 19·1 GHz are presented. The observed normalized brightness temperatures were used to estimate the soil moisture content using the radiative transfer model. It is found that the r.m.s. difference between observed and estimated soil moisture content is comparable to the standard deviation found in ground measurement of soil moisture content.     

Passive microwave remote sensing of soil moisture

Results of radiometric measurements over bare soil obtained with a horizontally polarized microwave radiometer at 19·1 GHz frequency are presented. Radiometer measurements were made with incidence angles varying from 10 to 50°. Ground-truth acquisition of soil moisture in the 0–1 cm layer and of soil temperature near the surface was made concurrently with radiometer measurements. The measured brightness temperatures over a bare field are higher than those calculated from an emmissivity model.     

Passive microwave sensing of soil moisture content: The effects of soil bulk density and surface roughness

Microwave radiometric measurements over bare fields of different surface roughness were made at frequencies of 1.4 GHz, 5 GHz, and 10.7 GHz to study the frequency dependence, as well as the possible time variation, of surface roughness. An increase in surface roughness was found to increase the brightness temperature af soils and reduce the slope of regression between brightness temperature and soil moisture content. The frequency dependence of the surface roughness effect was relatively weak when compared with that of the vegetation effect. Radiometric time-series observations over a given field indicate that field surface roughness might gradually diminish with time, especially after a rainfall or irrigation. The variation of surface roughness increases the uncertainty of remote soil moisture estimates by microwave radiometry. Three years of radiometric measurements over a test site revealed a possible inconsistency in the soil bulk density determination, which is an important factor in the interpretation of radiometric data.     

Effects of corn stalk orientation and water content on passive microwave sensing of soil moisture

A field experiment was conducted utilizing artificial arrangements of plant components during the summer of 1982 to examine the effects of corn canopy structure and plant water content on microwave emission. Truck-mounted microwave radiometers at C (5 GHz) and L (1.4 GHz) band sensed vertically and horizontally polarized radiation concurrent with ground observations of soil moisture and vegetation parameters. Results indicate that the orientation of cut stalks and the distribution of their dielectric properties through the canopy layer can influence the microwave emission measured from a vegetation/soil scene. The magnitude of this effect varies with polarization and frequency and with the amount of water in the plant, disappearing at low levels of vegetation water content. Although many of the canopy structures and orientations studied in this experiment are somewhat artificial, they serve to improve our understanding of microwave energy interactions within a vegetation canopy and to aid in the development of appropriate physically based vegetation models.     

Thermal microwave emission depth and soil moisture remote sensing

This paper presents some additional theoretical and experimental results on the problem of estimating the soil depth to which soil moisture can be directly measured by VHF radiometers. The experimental work was implemented in August 1992 at the Research Farm of the Institute of Hydrotechnique and Amelioration, Sofia, Bulgaria. The soil thermal microwave emission was measured by an L-band Dicke-type radiometer at 1.65GHz at off-nadir angle from 20 to 60. It was found that the value obtained for the effective penetration depth depends on the definition used in the analysis: the definition of penetration depth is based on soil thermal emissivity or soil reflectivity. Further it was found that the depth to which the soil moisture can be directly measured exhibits a negligible dependence on polarization (horizontal, vertical) as well as on off-nadir observation angle. For the purpose of soil brightness temperature and soil reflectivity computing, a fast and robust method and algorithm were proposed which are based on Kong's coherent soil model. The experimental measurements were used to verify the model fitting to experimental conditions and results.     

Active microwave measurement of soil water content

Measurements of radar backscatter from bare soil at 4.7, 5.9, and 7.1 GHz for incident angles of 0–70° have been analyzed to determine sensitivity to soil moisture. Because the effective depth of penetration of the radar signal is only about one skin depth, the observed signals were correlated with the moisture in a skin depth as characterized by the attenuation coefficient (reciprocal of skin depth). Since the attenuation coefficient is a monotonically increasing function of moisture density, it may also be used as a measure of moisture content over the distance involved, which varies with frequency and moisture content. The measurements show an approximately linear increase in scattering with attenuation coefficient of the soil at angles within 10° of vertical and all frequencies. At 4.7 GHz this increase continues relatively large out to 70° incidence, but by 7.1 GHz the sensitivity is much less even at 20° and practically gone at 50°.An inversion technique to determine how well the moisture content can be estimated from the scattered signal indicates good success for near-vertical angles and middle ranges of moisture density, with poorer success at smaller moisture densities and an anomaly in the data at the highest moisture density that must be resolved by further experimentation.     

微波检测粮仓储粮水分技术的研究

分析了微波水分检测技术的原理、特点及所采用的方法。针对微波透射过粮食后,其反射波的能量衰减,信号参数变化与介电常数及粮食水分含量之间的关系,构建了储粮水分检测模型。测量结果与传统的烘干法所得到的水分含量比较,比较结果表明,利用微波法能够快速、准确地检测出储粮水分含量,满足粮仓储粮含水量检测的需求。     

Effect of vegetation on soil moisture sensing observed from orbiting microwave radiometers

The microwave radiometric measurements made by the Skylab 1.4 GHz radiometer and by the 6.6 GHz and 10.7 GHz channels of the Nimbus-7 Scanning Multichannel Microwave Radiometer were analyzed to study the large-area soil moisture variations of land surfaces. Two regions in Texas, one with sparse and the other with dense vegetation covers, were selected for the study. The results gave a confirmation of the vegetation effect observed by ground-level microwave radiometers. Based on the statistics of the satellite data, it was possible to estimate surface soil moisture in about five different levels from dry to wet conditions with a 1.4 GHz radiometer, provided that the biomass of the vegetation cover could be independently measured. At frequencies greater than about 6.6 GHz, the radiometric measurements showed little sensitivity to moisture variation for vegetation-covered soils. The effects of polarization in microwave emission were studied also.     

Monitoring agricultural soil moisture extremes in Canada using passive microwave remote sensing

Current methods to assess soil moisture extremes rely primarily on point-based in situ meteorological stations which typically provide precipitation and temperature rather than direct measurements of soil moisture. Microwave remote sensing offers the possibility of quantifying surface soil moisture conditions over large spatial extents. Capturing soil moisture anomalies normally requires a long temporal record of data, which most operating satellites do not have. This research examines the use of surface soil moisture from the AMSR-E passive microwave satellite to derive surface soil moisture anomalies by exploiting spatial resolution to compensate for the shorter temporal record of the satellite sensor. Four methods were used to spatially aggregate information to develop a surface soil moisture anomaly (SMA). Two of these methods used soil survey and climatological zones to define regions of homogeneity, based on the Soil Landscapes of Canada (SLC) and the EcoDistrict nested hierarchy. The second two methods (ObShp3 and ObShp5) used zones defined by a data driven segmentation of the satellite soil moisture data. The level of sensitivity of the calculated SMA decreased as the number of pixels used in the spatial aggregation increased, with the average error reducing to less than 5% when more than 15 pixels are used. All methods of spatial aggregation showed somewhat weak but consistent relationship to in situ soil moisture anomalies and meteorological drought indices. The size of the regions used for aggregation was more important than the method used to create the regions. Based on the error and the relationship to the in situ and ancillary data sets, the EcoDistrict or ObShp3 scale appears to provide the lowest error in calculating the SMA baseline. This research demonstrates that the use of spatial aggregation can provide useful information on soil moisture anomalies where satellite records of data are temporally short.