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The Bahamas Optical Turbulence Exercise (BOTEX) was conducted in the coastal waters of Florida and the Bahamas
from June 30 to July 12 2011, onboard the R/V FG Walton Smith. The primary objective of the BOTEX was to obtain
field measurements of optical turbulence structures, in order to investigate the impacts of the naturally occurring
turbulence on underwater imaging and optical beam propagation. In order to successfully image through optical
turbulence structures in the water and examine their impacts on optical transmission, a high speed camera and targets
(both active and passive) were mounted on a rigid frame to form the Image Measurement Assembly for Subsurface
Turbulence (IMAST). To investigate the impacts on active imaging systems such as the laser line scan (LLS), the
Telescoping Rigid Underwater Sensor Structure (TRUSS) was designed and implemented by Harbor Branch
Oceanographic Institute. The experiments were designed to determine the resolution limits of LLS systems as a function
of turbulence induced beam wander at the target. The impact of natural turbulence structures on lidar backscatter
waveforms was also examined, by means of a telescopic receiver and a short pulse transmitter, co-located, on a vertical
profiling frame. To include a wide range of water types in terms of optical and physical conditions, data was collected
from four different locations. . Impacts from optical turbulence were observed under both strong and weak physical
structures. Turbulence measurements were made by two instruments, the Vertical Microstructure Profiler (VMP) and a
3D acoustical Doppler velocimeter with fast conductivity and temperature probes, in close proximity in the field.
Subsequently these were mounted on the IMAST during moored deployments. The turbulence kinetic energy dissipation
rate and the temperature dissipation rates were calculated from both setups in order to characterize the physical
environments and their impacts. Beam deflection by multiple point patterns are examined, using high speed camera
recordings (300 to 1200 fps), in association with measured turbulence structures. Initial results confirmed our hypothesis
that turbulence impacted optical transmissions. They also showed that more research will be needed to better quantify
and mitigate such effects, especially for the U.S. Navy's next generation EO systems, including active imaging, lidar and
optical communications.
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