Transcript Laser Beam Propagation in Maritime Environment

Laser Beam Propagation in Maritime
Environment
Svetlana Avramov-Zamurovic Olga Korotkova Reza Malek-Madani
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Investigation Method
Laser Beam Propagation in Maritime Environment
Modeling
(Mathematics)
Field
Measurements
(Engineering)
Physical
Phenomenon:
Laser
Propagation
(Physics)
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Field experiments vs. Laboratory
Experiments in the laboratory provide controlled environment
for studding physical phenomena.
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Experiments often set up to observe a single parameter at the time.
Parameters could be changed independently from the rest of the
environment to isolate a particular effect.
Drawback:
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Even in the extraordinarily complex and resource rich laboratory not all
of the influential parameters of the maritime environment are included.
Field experiments provide the “real-life” conditions of the
environment on laser light propagation.
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True environmental changes along the entire path are occurring
simultaneously and influence laser light propagation.
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Temperature fluctuations, wind, aerosols, etc.
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Basic Field Experiment at USNA
Source:
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High quality beam shape (He-Ne red laser, Gaussian beam)
Low power laser (4mW), Midshipmen safety
Beam diameter suitable for medium range propagation (d=1cm)
Beam splitter and camera sensor used to observe beam statistics
Medium:
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Maritime environment at US Naval Academy grounds (propagation
across body of water and above field, 500m source-target distance)
Target:
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Light intensity fluctuations recorded at the beam center (observed
directly using camera sensor)
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College Creek Test
Weather conditions at Hospital Point on June18, 2010
Time
Temp
Humidity
Sea Level
Pressure
Wind Dir
Wind
Speed
Gust
Speed
Conditions:
9:54 AM
73.0 °F
57%
30.13 in
North
none
none
Clear
10:54 AM
75.0 °F
53%
30.13 in
none
none
none
Clear
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Measurements : Light Intensity Fluctuations
Objective: Laser light intensity fluctuations due to beam
propagation through maritime environment are recorded at the
source and at the target.
Statistical approach to analyze the beam propagation is the only
practical solution because it is impossible to instrument with
sensors the environment along the entire propagation path
outside of laboratory.
Actual measurement parameters:
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Area of observation 1cm2 at the beam center (stacked frames)
Spatial resolution far less than correlation distance due to high pixel resolution
of the camera’s sensor
Frame speed: realizations captured at the maximum rate of 1 kHz
3-5 minutes of continuous observations recorded
Weather parameters documented at target
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Model: Probability Density Function
The goal:
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Deliver laser light energy onto a target by maintaining the highest level
of light intensity for as long as necessary to interfere with the target.
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Environmental influences cause light intensity to fluctuate.
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Probability Density Function provides information on how often
particular light intensity occurs at the beam center, making PDF a
model of choice to measure the beam quality on the target.
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PDF contains the information about the properties of the environment the
laser light passed through.
The method:
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PDF models are based on light scattering physics employing various
mathematical functions and on statistical moments calculated from data.
Data histogram is used to evaluate the fidelity of a PDF model.
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Outcomes
Six field experiments successfully executed.
Students engaged in experimental aspect of the project:
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MIDN Iiams independent research studies
Field experiments are used as a laboratory exercise
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Control systems and their application to weapons course,
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A week per semester, 2 semesters, 3 sections, 50 students
Directed Energy course
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A week per semester, 2 semesters, 30 students
Four PDF models investigated:
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Gamma-Gamma and Log-Normal by Andrews and Philips, GammaLaguerre by Barakat and Rice–Nakagami modification by Beckman
Data processing programs developed in MATLAB.
PDF allowed us to clearly establish the difference between laser
beam propagation above water and over land.
Major project achievements published in a leading journal paper.
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Laser light propagation above the water
and above the land
Land
Water
Normalized Intensity
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Publications
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Journal
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Olga Korotkova, Svetlana Avramov-Zamurovic, Reza Malek-Madani, and Charles Nelson, "Probability
density function of the intensity of a laser beam propagating in the maritime environment," Opt. Express
19, 20322-20331 (2011)
Conference Proceedings
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Svetlana Avramov-Zamurovic ,Olga Korotkova and Reza Malek-Madani, “Probability Density Function Of
Fluctuating Intensity of Laser Beam Propagating in Marine Atmospheric Turbulence”, SPIE Photonics
West Sensing Conference proceedings, Atmospheric and Oceanic Propagation of Electromagnetic
Waves V,Volume 7924, (2011).
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C. Nelson, S. Avramov-Zamurovic, R. Malek-Madani, O. Korotkova, R. Sova, F. Davidson, “PDF
computations for power-in-the-bucket measurements of an IR laser beam propagating in the maritime
environment”, SPIE Defense, Security, and Sensing Conference proceedings, 2011.
Presentations
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Svetlana Avramov-Zamurovic, Olga Korotkova and Reza Malek-Madani,” Laser Beam Characterization of Propagation
through a Marine Atmospheric Channel”, Thirteenth Annual Directed Energy Symposium, November 2010.
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Svetlana Avramov-Zamurovic ,Olga Korotkova and Reza Malek-Madani, “Probability Density Function Of Fluctuating
Intensity of Laser Beam Propagating in Marine Atmospheric Turbulence”, SPIE Photonics West Sensing Conference,
January 2011.
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Reza Malek-Madani, Svetlana Avramov-Zamurovic, Olga Korotkova and Joe Watkins, “An experimental study of the
probability density function of a turbulence induced fluctuating laser beam”, Directed Energy Beam Control Conference,
May 2011.
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Next steps
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Education:
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Recruiting effort this fall resulted in three midshipmen already engaged in basic
experimental work with a goal to start independent research projects in spring.
Introduction to MATLAB programming as applied to modeling and processing
experimental data: a new 1 credit course offered to plebes.
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Research:
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To control light intensity delivery on the target modulate the light at the source
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Motivation: the first lecture will be collecting laser propagation data in HYDRO LAB.
SPACE domain:
TIME domain:
Pixel by pixel amplitude and phase modulation
Frame by frame modulation
Technical Support:
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Technician dedicated to the project made significant progress in establishing
instrumentation equipment functionality.
New instruments to be integrated into the project
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SPACE domain :
TIME domain :
Polarimeter
Spatial Light Modulator
Liquid Crystal Optical Modulators
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