Application Of Ultrasound And GPR Technology In The Detection Of Hard Foreign Objects In The Soil

Land farming is an extremely important part of agricultural production activities,land grader,rotary tiller and other land farming machinery in close contact with the topsoil soil in the work,the topsoil(within 40 cm from the surface)there is some hard foreign matter such as metal,stone and other objects will cause damage to the farming machinery,and in serious cases even endanger the safety of human and animal life.To address the problem of the lack of effective online monitoring of destructive hard foreign objects in the complex environment of farmland,this paper selects two mainstream non-destructive testing(NDT)techniques: ultrasonic NDT and ground-penetrating radar(GPR)to explore whether these two techniques can be applied to in situ,non-destructive detection of destructive hard foreign objects in topsoil so as to provide safety warning for soil farming machinery.The main tasks of this paper are:(1)Application of ultrasonic NDT technology in destructive hard foreign object detection.The application of ultrasound NDT technology to land farming machinery for the detection of destructive hard foreign matter in the topsoil layer.In this paper,we first set up a laboratory ultrasonic pulse velocity(UPV)test platform based on GB/T 50123-2019 and SY-T 6351-2012 standards to determine the acoustic parameters of the soil samples before and after the burial of hard objects;secondly,we evaluate whether ultrasonic NDT technology can be applied to the in-situ and non-destructive detection of destructive hard foreign objects in topsoil from the dimensions of pre-test preparation,actual testing,data collection,and analysis.The final results show that,although the acoustic parameters of the soil samples before and after burial in the UPV test are different,in order to ensure that there is sufficient energy at the transmitter end of the ultrasonic transducer to transmit into the soil sample and to receive as many echoes as possible at the receiver end,the necessary operations such as applying coupling agent to the transducer,posting aluminum foil and placing the transducer horizontally opposite to the other end of the transducer are required,which hinders the in-situ measurement of ultrasonic NDT technology in the agricultural environment,i.e.,the application of ultrasonic NDT technology is of low value.(2)Application of GPR technology in the detection of destructive hard foreign objects.In order to better interpret the detected GPR data,the open-source GPR numerical simulation tool gpr Max,based on time-domain finite difference method,is used in this paper to investigate the GPR reflection signal differences in terms of size,burial depth and shape of hard foreign bodies,and to evaluate whether the GPR technique can be applied to in situ,nondestructive detection of destructive hard foreign bodies in topsoil layers.The results show that: GPR technology can achieve non-destructive and in-situ measurement of destructive hard foreign matter,and the larger the size of hard foreign matter,the stronger the electromagnetic wave reflection signal;the deeper the burial depth,the weaker the electromagnetic wave reflection signal,the results of the numerical simulation is also confirmed in the hard foreign matter detection test below.(3)Research on GPR detection tests and data processing methods.For commercial GPR data processing software,there are issues of closed source,high cost of use,and lack of comparative validation in the GPR numerical simulation section above.First,a rigid foreign object detection model was established in the soil trough laboratory of South China Agricultural University,and the experimental data were collected by the MAL? GX GPR system(center frequency 750 MHz).Then,an R-based GPR data processing method is proposed in which the raw data collected is processed and analyzed using the RGPR tool in R.The final results show that: when the central frequency remains constant,the grayscale in the original GPR profile decreases as the burial depth of the hard foreign object increases,and the identification efficiency decreases;after processing the original data,a clear display of the hard foreign object can be seen in the GPR profile;after double-curve fitting of the processed data,the depth of the vertices extracted from the double-curve can be consistent with the burial depth of the experimental setup,and as the size of the hard foreign object gradually increases,the curvature of the double-curve also gradually increases,which is basically consistent with the numerical simulation results in this paper.