We implemented and validated a new method to estimate the velocity distribution from CO GPR data by using the reflection amplitudes and traveltimes picked on the interpreted interfaces in a GPR profiles. Since the method assumes the picked amplitudes to be related only to the reflection coefficients, an accurate data processing is essential before any amplitude picking, the most important steps being the amplitude recovery and the removal of scattering effects. The method also requires as input: 1) the value of the offset, 2) the velocity of the EM wave in the shallow layer, 3) the peak amplitude of the wavelet incident at the first interface. The error associated to the velocities in the first layer has the major influence on the uncertainties of the final results. Nevertheless, this error can be reduced by combining different independent measurements, like CMP gathers, TDR measurements, or dedicated trans-illumination experiments. The assumption of 1-D model in the proximity of each trace position, as well as the small spread approximation used in the algorithm, are acceptable for most of the real GPR applications. In fact, given the small offsets normally used for CO GPR surveys, the incident angles on the various interfaces are small even for shallow targets. The method assumes the subsurface material as lossless and non-dispersive. The latter assumption is satisfied for most practical applications, but most geological media are characterized by high intrinsic attenuation. In such conditions, the procedure could be still valid if applied on data properly corrected for dissipation effects. Further research must address this topic for a better understanding not only of the kinematic, but also of the dynamic behavior of the EM waves in real media at practical field conditions.

A new methodology to estimate the EM velocity from Common Offset GPR: Theory and application on synthetic and real data

DOSSI, MATTEO;FORTE, Emanuele;PIPAN, MICHELE;COLUCCI, RENATO
2013-01-01

Abstract

We implemented and validated a new method to estimate the velocity distribution from CO GPR data by using the reflection amplitudes and traveltimes picked on the interpreted interfaces in a GPR profiles. Since the method assumes the picked amplitudes to be related only to the reflection coefficients, an accurate data processing is essential before any amplitude picking, the most important steps being the amplitude recovery and the removal of scattering effects. The method also requires as input: 1) the value of the offset, 2) the velocity of the EM wave in the shallow layer, 3) the peak amplitude of the wavelet incident at the first interface. The error associated to the velocities in the first layer has the major influence on the uncertainties of the final results. Nevertheless, this error can be reduced by combining different independent measurements, like CMP gathers, TDR measurements, or dedicated trans-illumination experiments. The assumption of 1-D model in the proximity of each trace position, as well as the small spread approximation used in the algorithm, are acceptable for most of the real GPR applications. In fact, given the small offsets normally used for CO GPR surveys, the incident angles on the various interfaces are small even for shallow targets. The method assumes the subsurface material as lossless and non-dispersive. The latter assumption is satisfied for most practical applications, but most geological media are characterized by high intrinsic attenuation. In such conditions, the procedure could be still valid if applied on data properly corrected for dissipation effects. Further research must address this topic for a better understanding not only of the kinematic, but also of the dynamic behavior of the EM waves in real media at practical field conditions.
2013
9788890210198
9788890210181
http://www2.ogs.trieste.it/gngts/gngts/convegniprecedenti/2013/Riassunti/Atti32_vol3.pdf
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11368/2848300
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