Figure 5:

The range of depths that varied < ± 5% from the dispersion or attenuation estimate at the center of the excitation for HWR 8, 12, 16, and 20 in the VE material M4 (Table 2). Errorbars represent the variation seen over the frequency range of 100-400 Hz. As the height of the excitation increases the range of depths that give a consistent estimate also increases, although the range of depths for attenuation is always smaller than the range of depths for dispersion. The range of depths were symmetric about 60 mm due to the excitation symmetry above and below the center of the excitation as seen at 200 Hz in Figure 4. Note that these estimates do not take into account bias in an estimate, only the consistency of the measurement made.