Figure 11.
Time-frequency representation of a single impact (Left Column) and Fourier spectra of time windowed recordings (Right Column). The arrows indicate the frequency of the Impact-Echo resonance.
Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.