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Full-Text Articles in Physical Sciences and Mathematics
Instantaneous Spectral Analysis: Time-Frequency Mapping Via Wavelet Matching With Application To Contaminated-Site Characterization By 3d Gpr, John H. Bradford, Yafei Wu
Instantaneous Spectral Analysis: Time-Frequency Mapping Via Wavelet Matching With Application To Contaminated-Site Characterization By 3d Gpr, John H. Bradford, Yafei Wu
CGISS Publications and Presentations
Spectral decomposition, by which a time series is transformed from the 1D time/amplitude domain to the 2D time/spectrum domain, has become a popular and useful tool in seismic exploration for hydrocarbons. The windowed, or short-time Fourier transform (STFT) was one early approach to computing the time-frequency (t-f) distribution. This method relies on the user selecting a fixed time window, then computing the Fourier spectrum within the time window while sliding the window along the length of the trace. The primary limitation of the STFT is the fixed window which prevents either time localization of high frequency components (if …
Frequency-Dependent Attenuation Analysis Of Ground-Penetrating Radar Data, John H. Bradford
Frequency-Dependent Attenuation Analysis Of Ground-Penetrating Radar Data, John H. Bradford
CGISS Publications and Presentations
In the early 1990s, it was established empirically that, in many materials, ground-penetrating radar (GPR) attenuation is approximately linear with frequency over the bandwidth of a typical pulse. Further, a frequency-independent Q* parameter characterizes the slope of the band-limited attenuation versus frequency curve. Here, I derive the band-limited Q* function from a first-order Taylor expansion of the attenuation coefficient. This approach provides a basis for computing Q* from any arbitrary dielectric permittivity model. For Cole-Cole relaxation, I find good correlation between the first-order Q* approximation and Q* computed from linear fits to the attenuation coefficient …
A Field Comparison Of Fresnel Zone And Ray-Based Gpr Attenuation-Difference Tomography For Time-Lapse Imaging Of Electrically Anomalous Tracer Or Contaminant Plumes, Timothy C. Johnson, Partha S. Routh, Warren Barrash, Michael D. Knoll
A Field Comparison Of Fresnel Zone And Ray-Based Gpr Attenuation-Difference Tomography For Time-Lapse Imaging Of Electrically Anomalous Tracer Or Contaminant Plumes, Timothy C. Johnson, Partha S. Routh, Warren Barrash, Michael D. Knoll
CGISS Publications and Presentations
Ground-penetrating radar (GPR) attenuation-difference tomography is a useful tool for imaging the migration of electrically anomalous tracer or contaminant plumes. Attenuation-difference tomography uses the difference in the trace amplitudes of tomographic data sets collected at different times to image the distribution of bulk-conductivity changes within the medium. The most common approach for computing the tomographic sensitivities uses ray theory, which is well understood and leads to efficient computations. However, ray theory requires the assumption that waves propagate at infinite frequency, and thus sensitivities are distributed along a line between the source and receiver. The infinite-frequency assumption in ray theory leads …