| Plant water physiological information is closely related to plant life activities.Water not only plays an important role as an important component of plants,but also plays an important role in the material exchange between plants and the environment.In addition,the freeze-thaw situation of plants is also closely related to plant water during the winter.Research on methods that can effectively monitor plant moisture and freeze-thaw in the wintering period not only can provide guidance for agro-forestry production management,but also provide technical means and scientific basis for plant physiology research.In order to realize the real-time and on-line detection of stem moisture and freeze-thaw information of standing trees in forest,this paper proposes a method of stem moisture and freeze-thaw detection of standing trees.Based on this method,a corresponding sensor is developed and its performance tests are conducted.By applying it to the monitoring of living standing trees in forest,the change of moisture information and the freezing and thawing conditions of the overwintering period were investigated.The main research contents,methods and conclusions of this article are as follows:(1)Aiming at the physical characteristics and dielectric characteristics of the stem tissues of live standing trees,on the basis of the non-destructive real-time online detection method of stem moisture of living tree based on the standing wave principle proposed by the team in the early stage,the appropriate detection frequency was deeply studied,and the optimal detection frequency was determined to be 100 MHz.At the same time,a new spring steel strip probe capable of measuring stem moisture and freezing and thawing at the same time is designed.The measurement circuit is improved and the circuit is simulated and analyzed,the results show that the circuit meets the measurement requirements.The software and the overall structure of the sensor are designed.(2)The performance test of the sensor shows that the measurement result is stable and reliable.The results show that the linear model of the calibration model is more than 0.96,the radial sensitive range of stem moisture measurement is 32.5mm,the measurement range is 0% ? 100%,the resolution is 0.05%,the measurement accuracy is ± 1.76%,and the dynamic response time is 0.296 s.The radial range of the latent heat detection temperature is the length of the probe,the longitudinal range is 1mm,the measurement range is-40 ? ? 80 ?,the resolution is 0.10 ?,the measurement accuracy is ± 0.15 ?,and the dynamic response time is 1.88 s.Working current 0.05 A.At the same time,the analysis and comparative test of the influence of environment temperature,humidity,conductivity and diameter on the sensor show that the sensor meets the measurement requirements.(3)A method of stem freeze-thaw detection based on stem water envelope analysis was proposed.Aiming at the problem that the freezing and thawing information in stems of live standing trees during wintering is difficult to be detected online in real time,by studying the change in impedance during the freezing and thawing of stems,based on the freezing and thawing process is the conversion of liquid water and solid ice,an estimation model of stem volume ice content based on the envelope is established,which provides a method for evaluating the freezing and thawing status of stems in the overwintering period when only stem moisture data is available.(4)A method of stem freeze-thaw detection based on latent heat effect was proposed.In view of the deficiency of stem moisture envelope analysis method,based on stem temperature and stem temperature change rate index,the freeze-thaw point detection of stem was further carried out.The detection method of stem volume ice content and radial freeze-thaw depth was established.The real-time online detection of stem moisture and freeze-thaw of living tree was realized by embedding the model into the sensor.(5)In order to better apply the stem moisture and freeze-thaw detection to the growth of living standing trees,the monitoring of the stem moisture and the changes of freezing and thawing during the wintering period of living standing trees in different regions,results show that the sensor can effectively reflect the changes of water content and freeze-thaw in the growth process of living trees,and provide a new technical means for the production management and plant physiology research of agriculture and forestry. |
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