Basic Research On Key Technology Of Impulse Ground Penetrating Radar System

GPR(Ground Penetrating Radar)is a geophysical exploration method that detectthe distribution of underground media by UHF electromagnetic wave.It is widely applied to various near surface detection.GPR applications tend to diversify,including geological engineering exploration,sediment detection,glacier detection,military and archaeological exploration.The ground penetrating radar has the advantages of nondestructive detection,high efficiency,high resolution,and intuitionistic results.Due to the expansion of ground penetrating radar applications,has far exceeded the "ground" category,so far,GPR has become a routine detection technology,can solve a lot of practical exploration application problems,therefore,GPR system requirements are constantly improve,at present foreign commercial exploration there are many kinds of radar systems,but the price is expensive,therefore,the research and development of system technology of domestic radar GPR instrument and has important significance for the engineering application of geophysics.Impulse ground penetrating radar is a time domain GPR,also known as a carrier free ground penetrating radar.Time domain ground penetrating radar applications more widely,is a kind of ultra wideband radar,it will pulse of electromagnetic wave emitted by the antenna for one time,launch of a carrier free electromagnetic pulse signal,and the broadband receiver through the electromagnetic pulse echo signal in different medium,the electromagnetic wave will be different in different medium in the propagation path,waveform and intensity of electromagnetic field,analyzing the collected echo time,amplitude and waveform characteristics to determine the stratigraphic structure and the target information.The time domain of GPR based on pulsed GPR,it occupies a dominant position,in the commercial GPR in the use of simple,and impulse ground penetrating radar has advantages of detecting penetration ability,high resolution,low power consumption,simple structure,widely used in various fields of engineering geological exploration.The impact pulse ground penetrating radar system consists of the time domain pulse source,the transceiver antenna system,the data acquisition part and the data processing.This paper mainly studies a kind of impulse GPR system hardware,the main units of the system of basic research,research contents include pulse antenna source,acquisition and control system,by testing the design of the ground penetrating radar system,analysis of test results.First of all,this paper on the development stage of GPR and development at home and abroad in detail,introduces the GPR technology and theoretical basis,and gives the subsurface impulse overall design scheme and technical key technical indicators of radar system,the impulse GPR system,must choose the appropriate system parameters,including width,amplitude,pulse antenna signal center frequency,the sampling rate of the data.Secondly,the narrow pulse signal produced by avalanche effect is usually unipolar.However,the bipolar pulse signal is often needed in the actual detection radar device,so as to connect with the antenna.The pulse source of the ground penetrating radar designed in this paper can produce bipolar nanosecond pulse signal,and take avalanche transistor pulse generation circuit as the core,and use an avalanche transistor to generate a time domain impulse signal with a fast rising edge.The main factors that affect the output signal of pulse source are analyzed by using Multisim circuit simulation software,the parameters of components are reasonably set,the circuit structure is optimized,and the bipolar pulse source circuit based on avalanche transistor is made.The pulse source circuit designed in this paper is simple in structure,stable in performance,good in output waveform and no tailing phenomenon.The bipolar pulse signal,such as amplitude,width,frequency and repetition rate,can meet the basic requirements of ground penetrating radar system.Then,the ground penetrating radar antenna design and pulse source matching,probe antenna is an important part of the radar system,the antenna of ground penetrating radar system for broadband symmetric antenna,the antenna performance will affect the detection results of GPR,technical indexes of antenna to match each other with pulse source design,pulse signal feed to the antenna,the antenna design needs to consider the broadband signal center frequency selection.The typical antenna for impulse ground penetrating radar system is a butterfly shaped oscillator antenna or a dipole antenna.This paper designed the two kinds of antenna,bowtie antenna and planar dipole antenna is designed and analyzed using electromagnetic simulation software HFSS to study the shape and size of the GPR antenna,echo loss,analysis of antenna radiation performance,optimization of antenna model design,according to the simulation model,the antenna was fabricated.The actual antenna using the network analyzer test,the test results show that the design of GPR antenna has wide bandwidth,good directionality,time domain signal without distortion characteristics,excellent performance,two kinds of antennas can be designed for ground penetrating radar system.Finally,we integrate the pulse source circuit,the antenna system and the acquisition unit and verify the correctness and feasibility of the design of the impulse pulse GPR system through the whole test,and design the experimental scheme reasonably,and observe the acquisition results.First,we tested the direct and the reflected signals of the ground penetrating radar.The waveforms of the single channel data and the direct wave and reflected wave were all right and reasonable.In this paper,we use the common offset detection mode to collect data for the whole survey line.Because of the serious noise,we can de noise the collected GPR data,improve the imaging quality and highlight the location of the target.The results of ground penetrating radar data after noise reduction are analyzed.The target bodies in the measured section are clearly visible.The experimental results show that the designed impulse pulse ground penetrating radar system has the ability to detect the target body,and the whole system works stably.