TARIF, P. and BOURBIE, T. 1987, Experimental Comparison between Spectral Ratio and Rise Time Techniques for Attenuation Measurement, Geophysical Prospecting 35,668-680.Two techniques for the measurement of attenuation-spectral ratio and rise time techniques-were tested and compared in the laboratory. The spectral ratio technique proved to be reliable and easy to implement for intermediate values (5 < Q < 50) of attenuation. For low (Q > 50) and high attenuations, the spectral ratio technique is inaccurate. Calculating the rise time on simulated signals, we found a relation between rise time z and the ratio traveltime to quality factor T/Q which could be approximated in intervals by the linear relation z = zo + C*T/Q. The constants zo and C depend on the absolute value of T/Q and on the initial source signal. The rise time technique, performed on the first quarter period of the signal, enables high attenuations (Q < 5 ) to be measured. The determination of the relation between z and T/Q is possible if one knows the initial source. We theoretically approximate this relation through a simulation using a realistic propagation model. With laboratory measurements made on Fontainebleau sandstone, we show that the rise time technique using the theoretical relation z = z(T/Q) gives comparable values of Q to those obtained from the spectral ratio technique. In borehole seismics, where it is often difficult to remove undesired signals, the rise time technique applied with the right (7, T / Q ) relation is the best method to use.

The measurement of attenuation is performed by directly determining the attenuation operator (or the impulse response of the medium) in the time domain. In this way, it is possible to separate the attenuation operator from other non-attenuation effects, e.g. reflections. The Wiener filtering technique, or the damped least-squares, is used to calculate the attenuation operator. For the damped least squares, we have corrected for the effect due to the addition of the damping constant using a perturbation method. Numerical tests are carried out to illustrate the technique.The geometric beam spreading of ultrasonic waves generated by a source of finite size can strongly affect the result of attenuation measurements. Corrections are made by equating the received signal to the average pressure over the receiver surface.The technique is used to measure ultrasonic attenuation in water, glycerol and mud. The measurement in water offers a test of the corrections made for the geometric beam spreading. The measurement in glycerol and mud shows that, in the frequency range of 0.2-1.5 MHz, the attenuation of glycerol increases rapidly with frequency, whereas the attenuation of mud is proportional to frequency, exhibiting a constant Q behavior. The measurements show that the technique used here is an effective approach to the measurement of attenuation. 484Tang et al.

The measurement of attenuation is performed by directly determining the attenuation operator (or the impulse response of the medium) in the time domain. In this way, it is possible to separate the attenuation operator from other non-attenuation effects, e.g. reflections. The Wiener filtering technique, or the damped least-squares, is used to calculate the attenuation operator. For the damped least squares, we have corrected for the effect due to the addition of the damping constant using a perturbation method. Numerical tests are carried out to illustrate the technique.The geometric beam spreading of ultrasonic waves generated by a source of finite size can strongly affect the result of attenuation measurements. Corrections are made by equating the received signal to the average pressure over the receiver surface.The technique is used to measure ultrasonic attenuation in water, glycerol and mud. The measurement in water offers a test of the corrections made for the geometric beam spreading. The measurement in glycerol and mud shows that, in the frequency range of 0.2-1.5 MHz, the attenuation of glycerol increases rapidly with frequency, whereas the attenuation of mud is proportional to frequency, exhibiting a constant Q behavior. The measurements show that the technique used here is an effective approach to the measurement of attenuation. 484Tang et al.

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