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16 st / February 2016 www.sea-technology.com entation replicated three times at distance increments of 30 cm. Simultaneous deployment of multiple, matching sen- sors spatially separated but in the same orientation provides statistics on the natural spatial variability of the optical pa- rameters, distinct from any orientation effects. Other optical sensors mounted on the package were WET Labs ac devices and ECO scattering sensors. Suffcient buoyancy was added to the package to achieve free-fall descent rates that could range from 10 to 50 cm/s. Several strong particle layers were observed during the feld effort. Holographic Imaging A custom in-situ holographic video imaging system (HO- LOCAM) was developed to assess particle felds in the submi- cron to several-millimeter size range in undisturbed remote sample volumes. The HOLOCAM uses dual optical paths with different magnifcations to resolve different ranges of particle sizes. A far feld lens is used for each optical path to image volumes approximately 3.5 and 0.023 cm3, respec- tively, in the middle of a 4-cm open-path volume between light source and light collecting optical windows. Opti- cal windows are separated from the edges of sample volumes by at least 5 mm, so that any associated boundary layer effects are negligible for the modest descent rates of a free-falling package with slightly neg- ative buoyancy. Any preferential particle orientation can be imaged unambiguous- ly with HOLOCAM, and then compared to any deviations found between the oth- er bulk optical measurement techniques. HOLOCAM was deployed adjacent to a Nortek Vector ADV and Aquadopp to parameterize current velocities, shear and turbulence coincident with par- ticle observations. Preferential particle orientation was repeatedly observed in strong particle layers residing within shear layers in the pycnocline. Scanning Lidar A multi-angle scanning lidar was developed to scan backward scatter- ing and attenuation throughout a grid of subnanosecond pulses, the central portion of which overlapped with felds-of-view of four detector mod- ules. Optical properties were validat- ed using side-by-side measurements from conventional in-situ optical prop- erty devices through a wide variety of laboratory and operational environ- ments. Results demonstrated the abil- ity to correct for multiple scattering errors to retrieve accurate beam atten- uation profles through a distance consistent with analytical predictions. Our approach was to reconfgure the system to allow for beam attenuation and backscattering profles to be made at any combination of azimuthal and zenith angles over a total solid angle of 2π steradians (i.e., hemispherical). Measuring hemispherical attenuation and backward scattering with the lidar system through particle layers while (depth), but at different sensor orientations. The optical param- eters were angular scattering (also known as the volume scattering function, or VSF) and beam attenu- ation. Replicate sensors mounted in different orientations in adjacent sample volumes should read ap- proximately the same if the particle feld is completely randomly ori- ented; consistently diverging values would be expected if particles are preferentially oriented. The VSF between 10° and 170° was resolved with two custom Multi-Angle SCattering Optical Tool (MASCOT) sensors with identical optical geometries. Polarizers were also used on a flter wheel to resolve po- larized scattering parameters that are sensitive to particle orientation. Attenuation was measured with fve WET Labs C-Stars, covering three different orientations, with one ori- (Top to Bottom) Example profle of attenuation coeffcient (c pg ) measure- ments from September 22, 2015 in East Sound, showing a strong thin lay- er of particles centered at 2.2 m with FWHM width of 25 cm. The particle peak occurred within the pycnocline and a layer of shear vertical. HOLO- CAM particle feld image within a thin layer peak at 2.7 m depth observed September 22, 2015, dominated by the chain-forming diatom species Ditylum. Most chains are several millimeters long, signifcantly longer than observed in dis- cretely collected samples with benchtop microscopy due to breakage of the chains during handling. Clear North- South orientation of diatom chains was observed that was co-located with a signifcant North-South shear layer.