Waveform (Infrasound) Interpretation (5)
In some cases, it may be possible to use
infrasonic waveforms to directly recover volumetric fluxes. Note, however, that this type of modeling
requires lots of assumptions.
One place where such modeling may be appropriate is Erebus, where the
following is true:
1)Bubble
dimensions are small relative to the radiated infrasound wavelengths (i.e.,
the source is a point source).
2)Material
accelerations are subsonic (i.e., a linear acoustic source).
3)Initial
volumetric expansion is isotropic (i.e., a monopole).
4)The
surrounding medium out to where sound is recorded is largely homogeneous (i.e.,
pressure is assumed to drop off as 1/r).
With
these assumptions in mind, we can model the recorded infrasound pressure trace
(pm) as a time-series record of volumetric
acceleration (Lighthill, 1978) where:
Q is
the source volumetric acceleration
r is
distance to sensor
c is
the speed of sound
