Research And Design Of Data Acquisition System In Airborne Ground Penetrating Radar

Airborne ground penetrating radar is a form of ground penetrating radar(GPR).Compared to conventional ground penetrating radars,airborne ground penetrating radars can survey areas that are hazardous or inaccessible by human beings.First of all,the airborne pulsed ground-penetrating radar echo signal is an ultrawideband signal.Using real-time sampling,the system has a complex design,high cost,and large power consumption.Analyzing the working principle of the pulse signal source,it is concluded that the voltage value of controlling the switching state of the avalanche transient pulse source is not an accurate value.This level of uncertainty causes the pulsed ground-penetrating radar signal and echoes to have random jitter characteristics over a range of time.This random jitter makes the radar echo signal and the sampling system have a certain non-correlation.The above situation brings two problems to the echo acquisition: first,simply using sequential equivalent sampling can not correctly reconstruct the echo waveform;second,the echo signal has relatively small random jitter relative to the sampling clock,making It difficult to capture a full sample clock cycle by the random equivalent sampling.In view of the above problems,this paper proposes a method of combining interval measurement with a delay chip.Among them,measuring the time interval between the sampling trigger signal and the sampling clock solves the first problem;the delay chip adjusts the phase of the echo signal and the sampling clock by step,solving the second problem.A random equivalent acquisition system based on Field Programmable Gate Array(FPGA)controller was designed to achieve radar echo signal acquisition and waveform reconstruction.The key technology of random sampling-time interval measurement circuit and pre-trigger function are discussed in depth.In addition,a signal conversion circuit scheme for correctly receiving ns-level trigger pulses is also provided.Second,this paper elaborates the design and implementation of an airborne stepfrequency GPR data acquisition system.By theoretically deducing and numerically simulating the signal flow of a stepper radar system,the signal characteristics of the stepfrequency ground penetrating radar are demonstrated.According to these characteristics of the stepped frequency signal,an acquisition system scheme that filters,buffers,and transmits quadrature baseband signals is proposed.Finally,the core modules of power supply,clock,data acquisition,and communication of the above two data acquisition systems are debugged to ensure that the entire data acquisition system completes the preset function.At the same time,the two acquisition systems were tested in conjunction with other modules of ground penetrating radar to verify the overall radar system performance.The airborne ground-penetrating radar performs ground layer target detection experiments on the ground to realize accurate identification of shallow ground metal targets.The airborne stepping frequency ground penetrating radar conducts closed-loop test experiments on the coaxial line,and each unit of the radar system operates normally.