Research Of Soil Moisture Detection Method And Its Application In Soil Freeze-thaw Cycle

Soil moisture monitoring,as an important part of the fine water-saving irrigation technology,plays a critical role in irrigation and the development of water-saving agriculture.Soil moisture monitoring is mainly for unfrozen soil,and for frozen soil is rarely mentioned in the current studies,more often than not the reason might be found in poor technology to obtain variables(ice,liquid water content,frozening depth)of frozen earth accurately,reliably,conveniently and in real time.Therefore,based on the theory of soil dielectric,combined with innovative measurement methods and experiments,a soil profile non-contact sensor was designed and two kinds of soil moisture measurement methods and a method for estimating ice content in field soil.So,it is effective to overcome the frozen soil cementation and the effects of change of soil composition on soil moisture monitoring in winter,this paper provides a theoretical and experimental basis for seasonal monitoring of soil moisture.The main contents and conclusions in this paper are as follows:1.Based on the in-depth study of various soil moisture measurement techniques,a ring probe structure suitable for non-contact measurement is designed according to the principle of edge field effect in electromagnetic field.The impedance and electric field distribution of the probe are analyzed by using the network vector analyzer and HFSS software.The results provide a theoretical basis for the design of non-contact soil profile moisture sensor.2.The soil profile moisture sensor based on the frequency domain measurement principle was studied and tested,and the performance of the sensor was studied and analyzed in the laboratory environment.3.Synthesizing the requirements of soil moisture monitoring,two kinds of soil profile moisture measurement methods were put forward.One is "a method to acquireb the information of multi-layer soil profile water",and another is "a method of soil profile moisture detection based on linear scale expansion".4.According to the dielectric equivalent principle in freeze-thaw and dry-wet cycle process,the feasibility of the detection system in measurement of liquid water content in the frozen soil is verified.In order to inspect the reliability of the system in frozen soil measurement,the freezing model of soil was established by experimental method,and the model was validated.5.To realize the real-time estimation of ice content in frozen soil,an estimation method of soil ice content and freezing degree index were proposed.And two concepts provided theoretical support for real-time monitoring of soil moisture.6.To collect and analysis of soil freeze-thaw cycle in Xiaotangshan,Beijing City and Pingquan,Hebei Province,which provided data support for the analysis of the freeze-thaw laws of the soil in Pingquan and Xiaotangshan.