| Nowadays, road construction in our country is developing very rapidly. Road quality examination and evaluation will be increasing dramatically. The method of thickness examination such as bore and sampling will not meet the demands, because they have many disadvantages such as low efficiency, bad representation and destruction. Therefore, a new, rapid, high-precision, effective and nondestructive technology is required to meet the engineering demand. Ground Penetrating Radar (GPR) for road detection is one of such a nondestructive technology.The principle of GPR is similar to the ordinary radar. It works near the surface of the road and transmits electromagnetic (EM) wave to the pavement layers. When the electromagnetic wave propagates in the pavement layers, it will be reflected at the interface of two different kinds of medium. As we know, different medium have different dielectric constant. The reflected wave will be received by the receive antenna and transferred to digital data. We can analyze the data that saved by the computer of GPR to deduce the medium's property, situation, location and so on. Being a kind of nondestructive, untouched method, it has many advantages such as high precision, low cost, abundant content, nondestruction and rapidness. It can collect data at the speed of 80 km/h. the data can be processed by special software and the GPR can offer color images and information of road service level. We can take some measure to rehabilitate road according to the data that GPR provides.But up to now, GPR data interpretation can't be automated eventually because of many artificial factors. Therefore, the result is subjective and incorrect. Therefore, we need make automated software quickly. Making software is based on algorithm, namely, the mathematic model of EM wave propagation. Then echo wave simulation is used to examine the model, because echo wave simulation is one of the effective manners to evaluate the propagation theory. Therefore, we can model the echo wave of the pavement structure that we have already knownand compare it to the actual wave. If they do not match very well, we can adjust some parameters to improve it. In the past, many scholars researched on it, but they didn't agree on it. The difference among them is so big that we don't know what to choose to analyze the roads in our country. To find out the propagation theory that suits to roads in our country, we have a series of research on it.In this dissertation, we focus on the issues that we described in the context and have a deep research on them. Performance & parameters of GPR, the dielectric property of pavement material, echo wave simulation technology are analyzed theoretically. Through this research, we attained some conclusions and results:Firstly, the theory of the EM propagation in pavement medium is analyzed systematically. Based on the Maxwell equation, the formula of transmittance constant, attenuation constant, phase-motion constant, reflected coefficient, transmitted coefficient, reflected electric field and transmitted electric field are deduced; The principle and method of dielectric constant backcalculation are studied; the mathematic algorithm is established primarily.Secondly, performance & parameters of GPR are analyzed theoretically for the design of practical GPR system and field application. In this dissertation, the formula of the performance & parameters of GPR are deduced theoretically and then the principle of parameters choice is presented briefly. First, We should deduce the resolution and the depth of the object according to actual situation. Second, we choose the antenna that has suitable central frequency. Finally, sampling interval and scan interval can be gained.Through the research, we can find out: (1) performance of GPR is determined by two factors: radar system and the object property. The central frequency is crucial and has obvious effect on GPR performance. In term of central frequency, the detection depth and the resolution are paradoxical. Higher the central fre... |
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