The spectrogram on the
next page shows the evolution of frequency spectra over time,
where the y-axis is the frequency axis.
In this figure, spectral amplitudes are plotted according to
an arbitrary color map. In this case,
dark blue is low amplitude and both lighter and hotter colors are
high amplitude. Note that from the spectrogram
one can immediately discern frequency content differences in the two events
occurring after 2500 s.
Note: we can also look at acoustic data in
spectrogram form.