Research On Dam Monitoring System Based On LoRa Broadcasting High Precision Differential Positioning

In recent years,the heavy rainfall caused by abnormal climate has put forward an extremely severe test for flood control and flood fighting work in our country.As a key point of flood control work,dams must be effectively monitored for deformation.GNSS positioning technology has become one of the research hotspots in the field of displacement and deformation monitoring due to many advantages,such as high precision,all-weather,real-time and so on.At present,most GNSS receivers are multi-frequency and multi-mode,which are very expensive.Although the static positioning accuracy can reach millimeter level,its cost exceeds the cost and real-time requirements of most structural deformation monitoring.Therefore,this paper studies the principle of carrier phase differential positioning,and designs a set of deformation monitoring system,based on the LoRa high-precision differential,which has the characteristics of low cost and simple deployment.It is of great significance to promote the application of GNSS positioning technology in the field of deformation monitoring.In this paper,the dam deformation monitoring system is proposed,based on the carrier phase difference algorithm using low cost single frequency GNSS module.The differential positioning technology and system are deeply studied.The basic principle of GNSS satellite navigation and positioning,the source of positioning error and the method of correction are introduced in detail.Then the pseudorange differential and carrier phase differential positioning methods are studied.The most critical whole-circumference ambiguity solving process in the carrier phase difference algorithm is expounded,and the most mature LAMBDA algorithm is studied.Then,it innovatively proposed to use KMeans clustering algorithm to eliminate the abnormal data of differential positioning.In the attitude calculation part,the Kalman filter is used to data fusion of gyroscope and accelerometer,and the proposed algorithm is simulated by MATLAB,which proves the feasibility of algorithm,and the algorithm is applied to the project through programming.Secondly,a hardware platform is constructed for the design of the monitoring system.The system is mainly aimed at the hardware design of the mobile station with low cost and high performance including microprocessor module,NEO-M8 T positioning board module,attitude detection module and other circuit design.After testing,the mobile station's differential performance is shown to be close to the professional Novatel satellite measurement board,which is about one-twentieth of the price.A large number of differential messages,such as ephemeris,pseudoranges,carrier phases,Doppler frequency shifts and CNR observations,are transmitted between the base station and the mobile station.In this paper,the LoRa technologyis used to broadcast differential messages to mobile stations,effectively reducing data transmission cost.Then GPRS is used to forward the positioning results to Web clients through the server.In the software system,the differential software is mainly designed for differential positioning solution,the server is used for data processing and forwarding monitoring data,and the web client is used to display monitoring conditions.Finally,the monitoring accuracy of the system is tested outdoors and the data are analyzed.The experimental results show that the differential positioning accuracy of the designed cost-effective mobile station is similar to that of the professional-grade satellite measurement board and the static positioning accuracy can reach centimeter level.The accuracy of the attitude measurement reaches 0.02?,which can achieve the purpose of dam deformation monitoring.The system designed in this paper adopts a self-designed and cost-effective receiver,low-cost data transmission and the accuracy meets the requirements with a wide range of practical application prospects.