| Ground penetrating radar (GPR) is a new type and effective detecting equipment for objects under shallow ground. The transmitting antenna transmits high-frequency wide-band electromagnetic waves into the underground, and the receiving antenna receives the echo signal reflected from the underground. Compared with other normal detection method, GPR has the advantages of rapid detection, high resolution, easy operation, non destructive testing, low cost, etc. So, it is widely used in national defence and national economy departments.This thesis is based on the study of road detection radar of Wuhan Universty. A complet radar system structure is constituded on the base of a large amount reading of literatures both internal and domestic.The GPR is consisted by three parts:the antenna and transmission/receive system, the host computer and display part. One of the main functions of GPR is controlling the pulse transmission and receiving the echo signal, the other is to process the data received and then display the section plan. The host computor is the key part of GPR, it includes sampling, data collecting, time varying gain (TVG), storage, pre-processing and transmission. It also charges the creating of the time base signal and synchronizate signal, in this way, it controls the system efficienly. This dissertation mainly studies the theory analyse, design, software and hardware omplementation.The main content of this dissertation can be concluded as following:1. On the deeply analyzation of working principle of GPR and echo signal characteristic, complet GPR system structure is constituded. For the condiration of real-time system demand, a control system based on "PC+DSP+FPGA" three level control is adopted. At the same time, a optimized three levels pipeline for GPR data processing is proposed, which relies on the three level control structure. Such pipeline increases the throughoutput of the system.2. The realization of high performance sampling circuit is a key problem in radar echo receiving, which is a development bottleneck in GPR. For the frequency of the echo signal in impulse GPR is very high, it is difficult to be sampled in real-time way, a data collection system based on equivalent-time Sampling is designed, including the realization circuit. A new patten of two stages cascaded step system cuicurt is proposed, which both satisfying the sampling rate of the experimental system and the high resolution detection. 3. High resolution GPR raises a claim in data collecting and processing, so the relationship between the vertical resolution and sampling precision is studied, which provides the theoretical principle for the design of ns level step system. At the same time, considering of the transimission delay of step system, the system time sequencing is studied and formulas are derived to solve the problem which has a direction for design.4. To guarantee the real-time performance of data collecting and data transmission which based on DSP, the transfer way both adopted DMA. Based on the research of DMA timing sequence, we select FPGA to finish the timing match. The Time Varying Gain (TVG) and system power is introdunced.5. For the question of the pre-processing tache, the time distribution in the system is studied. Based on the research, a real-time denoising algorithm based on lifting wavelet transform (LWT) is realized on DSP. And parallel structure is adopted which can increases the calculation efficiency. |
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