土壤水分快速测量方法及其应用技术研究
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摘要
本文在国家科技部“九五”仪器仪表攻关项目的资助下(专题号：96-A23-02-010)，以土壤介电特性为研究的锲入点，对基于驻波率原理(Standing Wave Ratio—SWR)的土壤水分快速测量方法做了系统的理论分析和深入的性能分析研究，为研究开发成功SWR型土壤水分测量传感器奠定了基础，同时研制出与全球定位系统(GPS)联合使用的土壤水分空间分布速测仪样机。概括起来本文的研究内容主要有以下几点：
1．本文通过对土壤介电特性的理论分析，论证了利用高频或微波段内的介电常数实部来快速测量土壤含水量是一种灵敏度高、适应面宽、受土壤理化特性空间变异影响较小的快速测量方法。为研制开发基于驻波率原理的SWR型土壤水分传感器奠定了基础。
2．建立SWR型土壤水分探头的特征阻抗模型是本文研究的重点之一。本文将四针等长式结构的土壤水分探头看成是同轴传输线的特殊形式，从标准传输线特征阻抗入手，结合平行传输线，运用数学上常用的夹逼定理，得出了四针等长结构的土壤水分探头特征阻抗数学模型，由此提出SWR型土壤水分四针不等长探头的特征阻抗数学模型。并通过大量试验验证了这一模型的正确性。
3．研究SWR型土壤水分传感器的测量敏感度是本文研究的另一重点。本文运用静电场分布的分析方法提出了四针等长结构式探针的敏感度数学模型，定性分析了SWR型土壤水分传感器的测量敏感度。提出SWR型土壤水分探头的测量敏感度是一个以中间探针为中心，半径小于中间探针与外探针之间距离、上粗下细的圆锥体，并通过大量试验验证了这一结论的正确性。
4．对SWR型土壤水分传感器的性能分析研究是本文的第三个重点。通过人量的室内试验验证了SWR型土壤水分传感器有很好的一致性，并通过大量试验数据分析说明土壤质地对SWR型土壤水分传感器的测量结果没有显著影响。特别是壤土、粘土、酸性粘壤土等土质对测量结果的影响达到了极不显著的水平，它们之间测量值的相关系数都达到了0.97以上。在德国联邦农科院的技术与生物系统研究所(FAL)的资助下，做了SWR型与TDR型、FD型土壤水分传感器的性能对比研究，结果进一步表明SWR型土壤水分传感器的测量结果不仅受土质的影响不明显，而且说明SWR型土壤水分传感器的性能与国外同类传感器相当。
5．本文从土壤墒情监测和指导田间变量灌溉的要求出发，研制开发了连接Ag132GPS接收机和SWR型土壤水分传感器的TSCⅣ型智能化土壤水分空间分布速测仪样机，完成了GPS数据的接收与处理、土壤水分的采集与保存等工作。并应用GIS软件ArcView生成了土壤水分分布图，由此来监测土壤水分墒情和指导田间变量灌溉。
As part of the Nationa1 "9'5" key project (No.f 96-A23-02-010) on instrUmentation suPPorted by the
Ministry of Science & Technology Ministry this study took the behavior of soil-water-system
dielectrics as a key point for further development and evaIuation of a new kind of Standing WaVe Ratio
(SWR) soil moistufe measuring system. A series of academic analysis and a lot of experiment
research on SWR4ased soil moisture sensor were catried out and presented in this paPer. On the basis
of the research, a new soil moisture sensof, which it is very suitab1e fOr field use, was developed. At the
same time, a new system to measure the spatial distributions of soil moistllre, which can be used
combining with Global Positioning System (GPS), was developed too. Ih generaI, the stUdy reported in
this dissettation can be briefly suonarized as follows f
l. Through theoretical analysis on the behavior of soil-water-system dielectrics, it is proved that the
real parts of the dielectric constant under high frequency or microwave can be used to measure soil
water content raPidly This method can get a lot of measurement results with high accuracy and
wide aPplicabiIity In addition, the results are seIdom affected by the spatiaI variation of soil
property As a further aPplication of the above result, a soil moisture sensor based on Standing
Wave Ratio was developed.
2. In this dissertation, a key point of the study is to build up a mathematical model of the character
imPedance the SWR sensor. The strUcture of four equal-length probes can be viewed as a special
fOrm of coaxial hansnussion line. Combining the character imPedance of coaxial and the para1lel
transmission line, the character imPedance model of probe with eqtlaling length was built uP by
utilizing mathemaical theory of aPproach. And then, the character imPedance model of SWR probe
was built uP and validated by experiments.
3. The spatial sensitivity of SWR sensor was another key poiflt in this study By analyzing electrostatic
distribution around probes, it was fOund that the spatia1 sensitivity ot SWR sensor is a cone whose
cellter is the mddle probe and radius is smal1er than the distance betWeen middle probe and around
probe. The correctness of this conclusion had been validated by experiments too.
4. Large amounts of lab exPerimellts showed that the consistency of SWR sensor is very good, and the
SWR sensor have excellent results in every kinds of soil texture, especially in loam, clay and acid
loam. There were not big variations among their measurement results. The correlative coefficient of
their measured data atrived at 0.97.
Under the suPport of Federal AghcuIturaI Research Center (FAL) of Germany, a series of
experimeflts had been done to compare SWR sensor with TDR sensor made by Germany and FD
sensor made by Holland. The results showed that the performance of the SWR sensor is as good as
other sensors. ln addition, the result further showed that the SWR sensor have excellent results in
every kinds of soil texture.
5. To meet the needs of soi1 moisture monitoring and vanabIe irrigation, a measurement system,
named Model TSCIV intelligent monitor, fOr measuring the spatial distributions of soil moistUre
was developed. SWR-based soil moisture sensor was combined or connected with Ag132 Global
Positioning System (GPS) in the system. The co1Iection and processing of GPS data and the
coIIection and saving of SWR data could be achieved, and the spatial distfibution map of soil water
content couId be protracted using ArcVew software of GIS. The system can be used to monitor soil
ll
water content and to further advise variable irrigation.
1．本文通过对土壤介电特性的理论分析，论证了利用高频或微波段内的介电常数实部来快速测量土壤含水量是一种灵敏度高、适应面宽、受土壤理化特性空间变异影响较小的快速测量方法。为研制开发基于驻波率原理的SWR型土壤水分传感器奠定了基础。
2．建立SWR型土壤水分探头的特征阻抗模型是本文研究的重点之一。本文将四针等长式结构的土壤水分探头看成是同轴传输线的特殊形式，从标准传输线特征阻抗入手，结合平行传输线，运用数学上常用的夹逼定理，得出了四针等长结构的土壤水分探头特征阻抗数学模型，由此提出SWR型土壤水分四针不等长探头的特征阻抗数学模型。并通过大量试验验证了这一模型的正确性。
3．研究SWR型土壤水分传感器的测量敏感度是本文研究的另一重点。本文运用静电场分布的分析方法提出了四针等长结构式探针的敏感度数学模型，定性分析了SWR型土壤水分传感器的测量敏感度。提出SWR型土壤水分探头的测量敏感度是一个以中间探针为中心，半径小于中间探针与外探针之间距离、上粗下细的圆锥体，并通过大量试验验证了这一结论的正确性。
4．对SWR型土壤水分传感器的性能分析研究是本文的第三个重点。通过人量的室内试验验证了SWR型土壤水分传感器有很好的一致性，并通过大量试验数据分析说明土壤质地对SWR型土壤水分传感器的测量结果没有显著影响。特别是壤土、粘土、酸性粘壤土等土质对测量结果的影响达到了极不显著的水平，它们之间测量值的相关系数都达到了0.97以上。在德国联邦农科院的技术与生物系统研究所(FAL)的资助下，做了SWR型与TDR型、FD型土壤水分传感器的性能对比研究，结果进一步表明SWR型土壤水分传感器的测量结果不仅受土质的影响不明显，而且说明SWR型土壤水分传感器的性能与国外同类传感器相当。
5．本文从土壤墒情监测和指导田间变量灌溉的要求出发，研制开发了连接Ag132GPS接收机和SWR型土壤水分传感器的TSCⅣ型智能化土壤水分空间分布速测仪样机，完成了GPS数据的接收与处理、土壤水分的采集与保存等工作。并应用GIS软件ArcView生成了土壤水分分布图，由此来监测土壤水分墒情和指导田间变量灌溉。
As part of the Nationa1 "9'5" key project (No.f 96-A23-02-010) on instrUmentation suPPorted by the
Ministry of Science & Technology Ministry this study took the behavior of soil-water-system
dielectrics as a key point for further development and evaIuation of a new kind of Standing WaVe Ratio
(SWR) soil moistufe measuring system. A series of academic analysis and a lot of experiment
research on SWR4ased soil moisture sensor were catried out and presented in this paPer. On the basis
of the research, a new soil moisture sensof, which it is very suitab1e fOr field use, was developed. At the
same time, a new system to measure the spatial distributions of soil moistllre, which can be used
combining with Global Positioning System (GPS), was developed too. Ih generaI, the stUdy reported in
this dissettation can be briefly suonarized as follows f
l. Through theoretical analysis on the behavior of soil-water-system dielectrics, it is proved that the
real parts of the dielectric constant under high frequency or microwave can be used to measure soil
water content raPidly This method can get a lot of measurement results with high accuracy and
wide aPplicabiIity In addition, the results are seIdom affected by the spatiaI variation of soil
property As a further aPplication of the above result, a soil moisture sensor based on Standing
Wave Ratio was developed.
2. In this dissertation, a key point of the study is to build up a mathematical model of the character
imPedance the SWR sensor. The strUcture of four equal-length probes can be viewed as a special
fOrm of coaxial hansnussion line. Combining the character imPedance of coaxial and the para1lel
transmission line, the character imPedance model of probe with eqtlaling length was built uP by
utilizing mathemaical theory of aPproach. And then, the character imPedance model of SWR probe
was built uP and validated by experiments.
3. The spatial sensitivity of SWR sensor was another key poiflt in this study By analyzing electrostatic
distribution around probes, it was fOund that the spatia1 sensitivity ot SWR sensor is a cone whose
cellter is the mddle probe and radius is smal1er than the distance betWeen middle probe and around
probe. The correctness of this conclusion had been validated by experiments too.
4. Large amounts of lab exPerimellts showed that the consistency of SWR sensor is very good, and the
SWR sensor have excellent results in every kinds of soil texture, especially in loam, clay and acid
loam. There were not big variations among their measurement results. The correlative coefficient of
their measured data atrived at 0.97.
Under the suPport of Federal AghcuIturaI Research Center (FAL) of Germany, a series of
experimeflts had been done to compare SWR sensor with TDR sensor made by Germany and FD
sensor made by Holland. The results showed that the performance of the SWR sensor is as good as
other sensors. ln addition, the result further showed that the SWR sensor have excellent results in
every kinds of soil texture.
5. To meet the needs of soi1 moisture monitoring and vanabIe irrigation, a measurement system,
named Model TSCIV intelligent monitor, fOr measuring the spatial distributions of soil moistUre
was developed. SWR-based soil moisture sensor was combined or connected with Ag132 Global
Positioning System (GPS) in the system. The co1Iection and processing of GPS data and the
coIIection and saving of SWR data could be achieved, and the spatial distfibution map of soil water
content couId be protracted using ArcVew software of GIS. The system can be used to monitor soil
ll
water content and to further advise variable irrigation.
引文
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