Quantifying optical aberration in the marine environment
Abstract
This proposal aims to study how laser beam quality degrades under the influences of the aerosol-laden boundary layer above sea-state, waves. This research combines our knowledge of the structure of high Reynolds turbulent boundary layers and the recently developed,laser-beam profiler that can image laser beam cross-section in detail.Recent discoveries in high Reynolds number turbulence reveal t,hat the spatial structure of atmospheric surface layers is distinct and heterogeneous. This distribution consists of large zones of,uniform streamwise momentum that are segregated by narrow ?fissures? of elevated shear (vorticity). At present, we hypothesise that,these internal interfaces (vortical fissures) constitute a primary source of optical scattering and attenuation. This project aims t,o understand the beam scattering mechanism, and if our hypothesis is true, we will develop a correlation between the laser beam prof,ile and the structure of the turbulence through which the laser beam passes.We will systematically divide this proposed research int,o two main components, with a decision point in between. The first part is to check if the heterogeneity of the turbulence field ind,eed plays a detectable role in the laser beam degradation, and if this correlation can be quantified. If the hypothesis is true, we,will elucidate these complex physics by performing detailed boundary layer measurements in our Extreme Air-Sea Interaction (EASI) fa,cility over a range of Reynolds numbers, while simultaneously quantifying the laser profile. On the other hand, if the hypothesis is, NOT true, we will instead perform a parametric investigation of laser beam degradation against aerosol concentration and sea-state,conditions, also in our EASI facility. This will allow us to create an empirical relationship between the sea condition, aerosol con,centration, and the expected laser aberration.The EASI facility is a 60-m long wave tank that can produce wind-wave conditions up to, category one hurricane. In addition, the facility has large sidewall windows for viewing access, allowing high-speed, high-resoluti,on Particle Image Velocimetry techniques to be used. The direct outcome of this 12-month research will be the knowledge of how stron,g shear layers within aerosol-laden ASL field affects optical degradation, and/or, empirical relationships between the sea condition,, aerosol concentration, and laser aberration.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 04, 2022
- Source ID
- N629092312009
Entities
People
- Joseph Klewicki
Organizations
- Office of Naval Research
- United States Navy
- University of Melbourne