The smaller vertical scales of sound speed variability of several recent deep water Pacific
Ocean acoustic experiments are extracted from individual conductivity, temperature, depth
(CTD) casts taken along the acoustic paths of these experiments, close to the times of
the experiments. The sound speed variability is split into internal wave variability and
spice variability, as these two parts obey very different dynamics %u2013 the internal waves move
through the water and the spice field moves with the water. Larger scales are mostly
responsible for acoustic travel time fluctuations, but smaller scales are mostly responsible
for other important phenomena such as intensity and arrival angle fluctuations. A method
is presented to determine when the two components are separable. The internal wave
properties are consistent with a spectral model such as a generalized Garrett%u2013Munk model,
whereas the spice is very intermittent, and the measurements are not extensive enough
to confidently make a spice model for acoustic propagation purposes. Both the internal
wave results and the spice results are summarized as vertical wavenumber spectra over a
selected vertical depth interval, but with the spice, it must be understood that a spectral
model would be very different from the data, and that the three-dimensional horizontal%u2013
vertical spectrum would be pure conjecture. The spectral level of the (small-scale) spice,
averaged over all the profiles, is comparable to that of the internal waves, suggesting that it
is not significantly less important to acoustic propagation than are the (small-scale) internal
waves.

In the spring of 2009, broadband transmissions from a ship-suspended source with a 284-Hz center frequency were received on a moored and navigated vertical array of hydrophones over a range of 107 km in the Philippine Sea. During a 60-h period over 19,000 transmissions were carried out. The observed wavefront arrival structure reveals four distinct purely refracted acoustic paths: One with a single upper turning point near 80 m depth, two with a pair of upper turning points at a depth of roughly 300 m, and one with three upper turning points at 420 m. Individual path intensity, defined as the absolute square of the center frequency Fourier component for that arrival, was estimated over the 60-h duration and used to compute scintillation index and log-intensity variance. Monte Carlo parabolic equation simulations using internal-wave induced sound speed perturbations obeying the Garrett–Munk internal-wave energy spectrum were in agreement with measured data for the three deeper-turning paths but differed by as much as a factor of four for the near surface-interacting path.