Electrode Arbitrary Distributed Electrical Resistivity Tomography Survey Design,Optimization And Preliminary Application

One of the most widely used geophysical surveying techniques in the urban environment is the geoelectric.And it has achieved good application effects in the fields of hydrology,engineering,archaeology and environmental investigation.Among them,electrical resistivity tomography(ERT)method is widely used because of its strong anti-interference ability,intuitive imaging results,and quick measurement.ERT exploration generally adopts regular grid and equidistant electrode arrangement,all electrodes are connected by long cables,and the opening sequence of electrode channels is controlled by the host computer to realize rolling measurement of multiple array types.The urban is a complex environment with high human interference such as high noise and high electromagnetic interference.And there are many buildings,irregular road and water systems,and the surface is highly concrete.It is difficult to meet the regular measuring layout or regular grid design and good grounding conditions required by the traditional method,which limits the application in the urban environment.Facing the demand for ERT in urban environment,this paper proposes a method for survey designing,data acquisition,data processing and optimization of electrode random distributed three-dimensional electrical method exploration system.Uniform standards for random dipoledipole arrays and non-standard array types to realize the arbitrary arrangement of electrodes according to ground conditions.On the basis of theoretical calculations,a set of data acquisition for random distributed ERT and data processing solutions are proposed.Based on the analysis of the arrays,this article first selects the dipole-dipole array as the basic unit and studies the constraints of the dipole array under three-dimensional conditions.By calculating the sensitivity,the overall coverage,and the geometric factor,the optimal value range of the length of the dipole pair,the distance,and the angle between the two dipole pairs is obtained.Based on theoretical analysis,the hardware framework of the data acquisition system is designed,and the wireless acquisition station with a pair of dipole electrodes connected by a short cable is used as the basic data acquisition unit(DAU).Each unit operates independently,and its length can be adjusted.They can be used as current or potential electrodes as needed.When one of the units serves as a current unit,the other units serve as potential electrodes and read at the same time.In this way,the restriction of regular grids and long cables in series can be eliminated,and parallel acquisition can be realized.Arbitrary distribution brings a high degree of flexibility and freedom of electrode layout,but also brings complexity to the design of the observation system and the method of data acquisition.Based on the effective measurement radius,the concept of "effective measurement circle" is proposed.That is,take the center point of a current pair as the center of the circle and draw a circle with the effective measurement radius.The other pairs in the circle are all measuring electrode pairs that meet the requirements and can be selected for parallel potential measurement at the same time.In order to make up for the insufficient density of measuring points caused by the preliminary measuring point design,or the problem of excessive density of measuring points,this paper proposes a "main-sub unit" solution.The preliminary design,all units have both current and potential functions,they are called the main unit.When the density of the measuring point is found to be insufficient,supplement the unit which is only used as the potential function;when the density of the measuring point is too large,part of the unit is only used as measuring electrodes.These units with only measurement functions are called sub units.This not only can effectively improve the density and resolution of measuring points,but also can effectively reduce the workload of data collection to achieve the purpose of efficient collection.In optimizing the selection of guide,the compared target resolution by batch method(CTRB)is used as the optimized array.It focuses on the target area and filters out data before the Compare-R calculation is applied.In the calculation process,the concepts of ‘batch' and ‘round' that are common in deep learning are introduced.By adjusting the batch size and select size,the calculation accuracy and calculation time can be artificially controlled.Using multiple batches of overall calculation,layer by layer,and multiple rounds of screening,it is suitable for real-time optimization of large amounts of data in the field.In addition,for the optimized set,the frequency and coverage range of its electrodes are analyzed,and some electrodes with low frequency are deleted.While the number of electrodes and configurations is reduced,a good resolution effect can still be maintained.Through the above calculation and analysis,the arrangement of electrodes and the selection of configurations can be guided,and the blind random distribution can be more orderly and efficient.Based on the arbitrary distributed ERT exploration design,the instrument system design,survey design and data acquisition process optimization are integrated into a whole to form a complete solution for urban complex environmental exploration.Finally,this paper proves that the complete solution of arbitrary distributed three-dimensional ERT design can work in the complex urban environment and achieve good results through actual cases.This provides a new way for geoelectrical in complex environments such as cities.