Spectral absorption of spatial and temporal ground penetrating radar signals by water in construction materials

This paper studies the spatial and temporal spectral absorption of reflector signals of a 1.5 GHz ground penetrating radar (GPR) during a drying process of a brickwall from initial wet to later dry state. The non-stationary GPR signals were processed with short time-Fourier transform (STFT) and wavelet transform (WT) in a novel spatial-time-frequency (STF) domain. Spatial distribution of peak frequency at the direct wave (DW) across the antenna and a backwall reflection was studied to characterize the mechanism of spectral absorption of GPR wave. Results from WT were shown to be more preferred to those from STFT because the WT offers multiple resolutions to cope with both low and high frequency components in GPR wavelets but STFT does not. In addition to the traditional GPR signal interpretation in time-domain and our previous works on time-frequency domain, the analysis method operated in the STF domain provides another possibility of material characterization by GPR in large and field scale.