Study On Fast-Measurement Of Soil Water Content And Application Technology

As part of the Nationa1 "9'5" key project (No.f 96-A23-02-010) on instrUmentation suPPorted by theMinistry of Science & Technology Ministry this study took the behavior of soil-water-systemdielectrics 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 experimentresearch on SWR4ased soil moisture sensor were catried out and presented in this paPer. On the basisof the research, a new soil moisture sensof, which it is very suitab1e fOr field use, was developed. At thesame time, a new system to measure the spatial distributions of soil moistllre, which can be usedcombining with Global Positioning System (GPS), was developed too. Ih generaI, the stUdy reported inthis dissettation can be briefly suonarized as follows fl. Through theoretical analysis on the behavior of soil-water-system dielectrics, it is proved that thereal parts of the dielectric constant under high frequency or microwave can be used to measure soilwater content raPidly This method can get a lot of measurement results with high accuracy andwide aPplicabiIity In addition, the results are seIdom affected by the spatiaI variation of soilproperty As a further aPplication of the above result, a soil moisture sensor based on StandingWave Ratio was developed.2. In this dissertation, a key point of the study is to build up a mathematical model of the characterimPedance the SWR sensor. The strUcture of four equal-length probes can be viewed as a specialfOrm of coaxial hansnussion line. Combining the character imPedance of coaxial and the para1leltransmission line, the character imPedance model of probe with eqtlaling length was built uP byutilizing mathemaical theory of aPproach. And then, the character imPedance model of SWR probewas built uP and validated by experiments.3. The spatial sensitivity of SWR sensor was another key poiflt in this study By analyzing electrostaticdistribution around probes, it was fOund that the spatia1 sensitivity ot SWR sensor is a cone whosecellter is the mddle probe and radius is smal1er than the distance betWeen middle probe and aroundprobe. 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 theSWR sensor have excellent results in every kinds of soil texture, especially in loam, clay and acidloam. There were not big variations among their measurement results. The correlative coefficient oftheir measured data atrived at 0.97.Under the suPport of Federal AghcuIturaI Research Center (FAL) of Germany, a series ofexperimeflts had been done to compare SWR sensor with TDR sensor made by Germany and FDsensor made by Holland. The results showed that the performance of the SWR sensor is as good asother sensors. ln addition, the result further showed that the SWR sensor have excellent results inevery 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 moistUrewas developed. SWR-based soil moisture sensor was combined or connected with Ag132 GlobalPositioning System (GPS) in the system. The co1Iection and processing of GPS data and thecoIIection and saving of SWR data could be achieved, and the spatial distfibution map of soil watercontent couId be protracted using ArcVew software of GIS. The system can be used to monitor soilllwater content and to further advise variable irrigation.