단시간주파수 변환을 활용한 자갈도상 오염에 따른 지표투과레이더 신호의 시간-주파수 특성 변화 연구

초록

The primary objective of this study is to use short-time and frequency transform to investigate the spectral and temporal variation of GPR signals measured over ballast with various fouling conditions. Four model specimens with dimensional sizes of 2000 mm×2000 mm×500 mm (width×length×depth) were fabricated in the laboratory to simulate four different fouling conditions in ballasted railway tracks, including a clean ballast (CB) specimen made with 100% clean gravel, a partially fouled ballast (PFB) specimen with sand-to-gravel volume ratio (S/G) of 50%, a fully fouled ballast (FFB) specimen with S/G of 100%, and a mixed ballast specimen (MIX) with 5 layers of different fouling conditions with S/G from 0% to 100% at intervals of 100 mm in depth. Three types of ground-coupled GPR with antenna frequencies of 400 MHz, 900 MHz, and 1600 MHz were used to measure GPR signals on the surfaces of the four model specimens. The results show that the time-frequency spectrum based on short-time Fourier transform (STFT) can describe the variation of spectral and temporal features of the four different ballast fouling conditions. It was observed that the center frequency of bottom reflection signals decreased in the three fouled ballast specimens (PFB, FFB, and MIX) compared to that in the clean ballast (CB) specimen. Particularly, scattering of GPR signals from the fouled ballast was greatly attenuated, with a value about 7dB lower than that from sound ballast.

키워드