The link between suspended particle fields, particle dynamics and bulk optical properties in natural waters is poorly
known because adequate technology is lacking to fully characterize critical parameters and interactions, especially for
ephemeral bubbles and aggregates. This paper highlights the capabilities of digital holography to provide non-intrusive,
high-resolution 3-D imaging of particles and bubbles in their natural environment. As part of a NOPP project
(HOLOCAM) to commercialize an in-situ digital holographic microscope (DHM), field data with a prototype in-situ
DHM (the "Holosub") were collected in East Sound, WA. The Holosub, an in-line holography based submersible
platform, was deployed in two configurations: free-drifting mode for vertical profiling, and towed mode. In free-drifting
mode, vertical profiles of shear strain and dissipation rates, undisturbed size and spatial distributions of particles and
organisms, and the orientation of diatom chains were recorded using the holographic images. Hydrographic and optical
data, as well as discrete water samples to identify phytoplankton species were concurrently collected. In towed mode,
the size and spatial distributions of bubbles just below the surface were recorded to characterize the dissipation of a
wake generated by another ship, and compared to optical and acoustic scattering data recorded simultaneously. Tools to
extract the size distribution and concentration of bubbles from the holographic data were developed. A preliminary data
analysis indicated high concentrations of bubbles detected by all three instruments at the same locations, while
comparison of the bubble size distributions indicated some similarities in trends, as well as significant differences.
Thin layers are water column structures that contain concentrations of organisms (or particles) that occur over very small vertical scales (a few meters or less), but with large horizontal scales (e.g. kilometers). Thin layers are now known to be common phenomenon in a wide variety of environments and can be a critical componant in marine ecosystem dynamics and functioning. While knowledge about their dynamics is important to our basic understanding of oceanic processes, thin layers can have significant impacts on both oceanographic and defense related sensing systems, e.g. thin layers can affect underwater visibility, imaging, vulnerability, communication and remote sensing for both optical and acoustic instrumentation. This paper will review the history of thin layers research, their ecological significance, innovations in oceanographic instrumentation and sampling methodologies used in their study, and the consequences of their occurence to oceanographic sensing systems.
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