Determination of Q-factor of Transmission Ground- Penetrating Radar Waves in Attenuating Media

Abstract

Electromagnetic wave attenuation in a medium is the primary parameter for interpreting Ground-Penetrating Radar (GPR) data. This attenuation manifests in wave energy absorption and velocity dispersion, which have different behavior depending on the rock type. Knowledge of the attenuation behavior of GPR waves in distinct media is, therefore, a success key to distinguishing rock types. The Q that is inversely proportional to the absorption coefficient represents its attenuation behavior. To observe the attenuation behavior of rocks, we conducted two different stages. The first stage is simulated the attenuation behavior by creating synthetic traces as a convolution between the wavelet and the corresponding impulse response. A Q-constant model and Futterman's velocity dispersion were used for the impulse response calculation. In the second stage, Q was determined using three different Q determination methods: the amplitude decay method, the spectral ratio method, and the Equivalent Bandwidth (EBW) method. Our research shows that due to the absorption, the wave amplitude becomes lower with increasing distance at the same Q, while at the same distance, its wavelength is longer, and its amplitude becomes low. The longer the distance at the same Q value, the narrower is the bandwidth of the transmission signals. We got a similar result with a small Q at the same distance length. At the same time, its peak frequency shifted to lower frequencies. Moreover, the applicability of the three methods for the determination of Q was investigated and tested on field transmission data acquired at the test field in the Reiche-Zeche Mine Shaft near Freiberg in Germany. Our investigation result shows that the three Q-methods were successfully applied to field transmission data resulting in comparable Q values ranging from 31 to 36 for gneiss rocks.