Gray line: acoustic field transmitted through the 64 mm thick bubble-gel mixture (in normalized amplitude). Black broken line: 2D diffusion equation for and .
Experimental setup. Left: the active experiment in the pulse-echo configuration. Right: the passive experiment in the transmission configuration before autocorrelation.
Example of two records and acquired at the same position (same transducer) but at two different dates. Between the two acquisitions, the temperature has increased by , which is hardly visible in the early part of the record (inset between 10 and ) but very clear in the late coda (inset between 42 and ).
Delay time evaluated for different lapse times in the coda from the doublet code. The broken line is the linear trend whose slope yields between and .
The correlation coefficient is evaluated at two temperatures for and 3 in the range. The maximum, obtained for a relative velocity change of , is indicated by the vertical arrow. It corresponds to an increase in temperature of . Theory is from Eq. (5).
The correlation coefficient is evaluated at two temperatures and 3 in the range, for various SNRs. Crosses indicate experimental data. The gray background indicates expected fluctuations [Eq. (11)] around the theory [Eq. (10)]. The proper velocity change is found in all cases, though a slight difference is visible for .
Relative velocity changes evaluated from the stretching (left) and for the doublet (right) technique for various SNRs. The actual is satisfyingly retrieved for any with the first technique, not with the second.
Comparison of the pulse-echo data obtained in the active experiment and the average autocorrelation .
Relative velocity changes evaluated from the active (pulse-echo with ) and the passive (autocorrelation with ) setup.
(a) The seismic noise source structure changes from one date to another. (b) Analogous laboratory experiment: Two sets of sources are chosen at two different dates.
Relative error in the estimation of , versus the ratio of unchanged-to-total amount of noise sources (-axis in logarithmic scale).
Comparison of the physical parameters between seismology and ultrasound.
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