| As a precious natural resource,groundwater is an important component of water resources and water systems,as well as a key element for the sustainable development of the ecological environment and economic society.The in-situ long-term monitoring of groundwater is the most reliable way to obtain real,real-time,continuous,and accurate groundwater information.In recent years,with the vigorous promotion of ecological civilization construction,the demand for multi-parameter groundwater sensors in in-situ long-term monitoring of groundwater has become increasingly clear and urgent.Compared to surface monitoring,in-situ long-term monitoring of groundwater is a special type of monitoring in a special environment.However,there are scientific issues and corresponding key technical issues in the in-situ long-term monitoring of groundwater,such as Lack of high-precision compensation method for wide temperature range,unclear drift patterns of electrode sensors,unclear intelligent recognition and compensation mechanisms,and inadequate adaptive adjustment methods with water environment.In response to the above issues,the response and behavioral characteristics of pressure,p H value and conductivity electrode sensors are systematically studied in this paper.On this basis,the new and complete set intelligent monitoring theory and method of multi-parameter in-situ long-term of groundwater are established.The main research work is as follows:Firstly,considering the significant differences of groundwater temperature and density with region,type and depth,a groundwater pressure monitoring method using the improved grey wolf optimization algorithm and surface fitting algorithm for the wide temperature and a groundwater level monitoring method with intelligent correction of water density were proposed.In order to overcome the limitations of the imbalance between global search and local development of the Grey Wolf optimization algorithm,an adjustable nonlinear convergence factor was designed to improve the optimization speed and accuracy of the optimization algorithm.In order to solve the problem of large fitting sample size and low fitting accuracy required for numerical calculation methods of wide temperature and wide range surface fitting,a wide temperature groundwater pressure monitoring method was formed using a surface fitting method and improved Grey Wolf optimization algorithm with the constraints of weight vector and weight interval coefficient.The measurement accuracy of the pressure and water level in a wide temperature range(better than 0.03%FS)and typical temperature range(better than0.02%FS)is further improved.Meanwhile,a water density intelligent calibration method was designed to improve the authenticity of monitoring the pressure and water level of different groundwater,especially high salt groundwater.Moreover,a direct comprehensive compensation method and a synchronous high-precision temperature measurement method was further developed with the pressure sensor alone.The new ideas and methods for improving the performance of pressure sensors and expanding their applications are supplied in complex groundwater environments such as geothermal energy.Secondly,aiming at the problem of p H monitoring data distortion caused by continuous drift of p H composite electrodes,a long-term in-situ dynamic monitoring method of p H composite electrodes based on the dual adaptive dynamic exponential smoothing method without periodic calibration was designed.The systematic experimental testing and research were conducted on the continuous drift behavior characteristics and related indicators of p H composite glass electrodes.According to the trend and behavioral characteristics of electrode drift at different stages,the exponential smoothing method was improved to achieve fast dual adaptive selection of exponential smoothing order and smoothing parameters with drift,and the intelligent recognition of p H electrode drift behavior and real-time accurate compensation of drift amount were implemented.Therefore,the new dynamic p H value quantitative calculation method was constructed with the p H electrode drift.The measurement error of this method is lower than 0.1p H in application,which provides an effective solution for groundwater in-situ long-term monitoring of p H value without correction.Thirdly,given the limitations of the existing four electrode conductivity monitoring methods including complex control timing,high software and hardware requirements,and poor compatibility between the method and the electrode,a synchronous rectification four electrode conductivity monitoring method based on intelligent optimization of frequency was designed.A single power supply half wave precision rectification technology method was designed,and the conversion of complex AC response signals to stable DC output signals under variable frequency and multiple effects was achieved to reduce the measurement complexity and hardware resource requirements.The intelligent adaptive frequency selection of AC excitation signals was achieved with the state tracking and judgment of the rectifier circuit.So that the problem of incompatibility between the method and different four electrode conductivity electrodes was solved,and the adaptability of wide range groundwater conductivity was improved.The measurement accuracy of the new method is better than 2.5%,which provides a new way for in-situ monitoring of groundwater conductivity over a wide range.Finally,based on the intelligent monitoring method of the above research,the multi-parameter in-situ long-term monitoring sensor for groundwater was designed.Two sets of designed multi-parameter sensors and a representative commercial sensor were installed together in groundwater monitoring wells to carry out the long-term(392 days)application experimental testing.The intelligent monitoring method studied and the excellent performance of its sensors were proved by the horizontal comparison between the monitoring data of the designed sensors and the vertical comparison between the monitoring data of different sensors. |
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