PURPOSES: The purpose of this study is to compare the advantages and disadvantages of 3D multichannel ground penetrating radar (GPR) equipment, which is mainly used for road cavity detection. The optimal signal analysis method was also proposed for 3D GPR data.
METHODS: Four types of 3D GPR equipment were used to detect road cavities in a pilot road section in Seoul. The obtained GPR signals were evaluated in the time and frequency domain using raw data. In addition, various types of filters were applied to time domain (B-scan) data to examine the optimal signal processing.
RESULTS: The time and frequency domain analysis of raw data showed that all the equipment produced reverse and strong signal reflections owing to the low dielectric permittivity of air in the cavity compared with neighbor materials. Also, the asymmetric parabolic curve was observed as well. The optimal signal processing method was determined to detect road cavities: zero-setting and background removal should be applied to all equipment. Bandpass filtering can be optionally applied to remove high-frequency noise or direct waves.
CONCLUSIONS: Despite the different specifications of GPR equipment in terms of signal generation and bandwidth, the GPR signals were appropriate in terms of zero-setting, noise level, and depth of investigation. Therefore, all the multichannel GPR devices evaluated were found to be suitable to detect road cavities located at depths of 1.0 and 1.5 m after the application of proper filtering process.