Research Of ECHO Signal Enhancement Of Vehicle-Mounted GPR

China has the first length of railway tunnel and high speed railway tunnel in the world. therefore, it’s very important to investigate the health of railway tunnel using a fast non-contact and non-destructive technology. in present, the ground penetrating radar(GPR) is widely used in the tunnel investigation, but the GPR with ground coupled antenna can not be used in the fast detection of tunnel health. the vehicle-mounted GPR tunnel detection system using air coupled antenna, which can be used in the normal operation condition of the train. the air coupled antenna is installed on the vehicle and away from the tunnel wall, which results in the attenuation of deep reflection echo signal. in order to improve the detection results, we study the signal enhancement method of deep reflection echo in this paper.In present, the radar deep reflection echo is mainly enhanced by post-processing software, the system noise is inhibited, but the interest signal isn’t be enhanced in this processing, and the signal-to-noise improve a little. in order to overcome this problem, we design a circuit that enhance the radar echo from the antenna before it is sampled, the system noise is unchanged in this processing, the designed circuit significantly improve the signal-to-noise of deep reflection echo, and compensate the signal attenuation caused by the antenna far away from the tunnel wall, moreover, we analyze the attenuation mechanism of electromagnetic wave based on the theory of electromagnetic wave propagation, and find that the spherical exponential compensation (SEC) gain is effective to enhance echo signal.The equivalent sampling theory is widely used in the sampling processing of vehicle-mounted GPR tunnel detection system, we do a lot of analysis of the theory foundation, digital analog conversion. sampling holding of the echo receiving system. we firstly propose equivalent tvg amplification based on equivalent sampling theory and our hardware, and design the tvg amplifier circuit, the test results show that maximum gain is 13 decibel of our tvg amplifier circuit, which can compensate the signal attenuation about 2.5 meter. the distance between the antenna and tunnel wall is up to 4.75 m using our research result, which can meet the challenge of health investigation of the railway tunnel in china.