Date of Award

Fall 12-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Ocean and Earth Science

Committee Director

Richard C. Zimmerman

Committee Member

Victoria J. Hill

Committee Member

Charles I. Sukenik

Committee Member

Brian Collister

Abstract

Oceanographic lidar systems remotely characterize the vertical structure of the upper ocean by recording the light backscattered from a laser pulse as it propagates through the water column. Historically these systems have been constrained by limited detection ranges, often capturing only a portion of the illuminated water column, typically fading to noise around the 10% isolume. A primary constraint has been the limited dynamic range of digitizers, which inhibits the ability to resolve both intense near-field and faint far-field backscatter signals within a single acquisition. To address this, we developed a novel optical lidar system incorporating gated photomultiplier tubes (PMTs) that activate at staggered intervals before and after the laser pulse. This gating strategy allowed for high-gain detection of weak signals at greater distances without saturation from strong surface returns. The system also incorporated a high-speed digitizer equipped with multiple digital amplification channels, improving sensitivity to low-intensity returns intended to extend the detection range deeper into the water column. Additionally, we explored the limits of miniaturization by designing a compact and energy-efficient variant integrating a low-output laser. Both systems were characterized via controlled benchtop experiments and validated through in situ comparisons of optical attenuation and linear depolarization ratios. Testing included a pool trial and a coastal transect in the Mid-Atlantic Bight off the coast of Virginia. The compact system (“Beauty”) successfully detected close-range backscatter and high scattering objects at range in the pool test but was overwhelmed by ambient sunlight, limiting its utility for daytime use. The more powerful laser system (“Beast”) resolved water column optical properties across all tests, although a ringing artifact in the offshore transect stations reduced signal retrieval at depth. However, the system demonstrated sensitivity to changing water conditions, and the ability to relate system attenuation to water column optical properties and estimate Chl a concentration from the linear depolarization ratio.

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DOI

10.25777/nj7q-bg07

ISBN

9798276041469

ORCID

0009-0006-9466-0422

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