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Reza Malek-Madani Svetlana Avramov-Zamurovic Joe Watkins Will Peabody Andrew Browning

Experimental study of the probability density function of the intensity of a turbulence induced fluctuating laser beam. Reza Malek-Madani Svetlana Avramov-Zamurovic Joe Watkins Will Peabody Andrew Browning United States Naval Academy Olga Korotkova University of Miami.

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Reza Malek-Madani Svetlana Avramov-Zamurovic Joe Watkins Will Peabody Andrew Browning

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  1. Experimental study of the probability density function of the intensity of a turbulence induced fluctuating laser beam Reza Malek-Madani Svetlana Avramov-Zamurovic Joe Watkins Will Peabody Andrew Browning United States Naval Academy Olga Korotkova University of Miami

  2. Atmospheric signature from collected data at the receiver • The main goal of this effort is to characterize the signature of the atmospheric turbulence inherent in a medium from the beam data collected at a target. • The analysis presented here involves two sets of data, one collected in a laboratory setting, and the other from field experiments, both carried out at the Naval Academy. • Our first attempt in characterizing the signature is based on computing the probability density functions (pdfs) associated with data. • Our computational methodology is based on constructing pdfs using the Gamma-Gamma (Andrews and Phillips) and Gamma-Laguerre (Barakat), in hoping of discovering if either one is capable of quantifying the turbulence in the medium. United States Naval Academy

  3. Outline • Experiment: • Instrumentation set up in the field at the United States Naval Academy • Measure intensity statistics of the beam in its transverse cross-section during daylight. • Using precision instrumentation in the DE Beam Control Lab, compare to field measurements • Theory: • Calculations of statistical moments of intensity • Apply two PDF reconstruction models • Data comparison United States Naval Academy Distribution A

  4. Field setup one Target is a white board. Light intensities amplitude range of 255 was measured. Sequencing 30 frames per second - three minutes of data collected. Pixel size was effectively measuring 0.3 mm2 . United States Naval Academy Distribution A

  5. Field setup two United States Naval Academy Distribution A

  6. Field setup three Target is ccd sensor with 633 nm notch filter. The sensing area is 7.6 mm (horizontal) × 6.2 mm (vertical) with pixel size of 4.65 μm. United States Naval Academy Distribution A

  7. Lab setup Tunnel Target Table Source Table Isolators United States Naval Academy Distribution A

  8. Laser Lab setup - schematic Target Phase Screen 36 in L1 L2 L3 X axis Source Table Z axis Target Table

  9. Lab setup - source Target Phase Screen Source Laser 2 mWHeNe United States Naval Academy Distribution A

  10. Lab setup – phase screen United States Naval Academy Distribution A

  11. Lab setup - target United States Naval Academy Distribution A

  12. Quantifying the turbulence in the lab setup United States Naval Academy Distribution A

  13. Temperature and Centroid Fluctuations – Lab Setup United States Naval Academy Distribution A

  14. Histogram of data from labno heat vs phase screen, hot pixel * No heat * Phase Screen # of occurrences Intensity, cts United States Naval Academy Distribution A

  15. Probability Distribution Function Reconstruction Methods • Gamma distribution modulated by series of generalized Laguerre polynomials proposed by Barakat • Medium and source independent • Uses first n moments of detected intensity • Valid in the presence of scatterers • Gamma- Gamma distribution based on the work of Nakagami et al. and presented by Andrews and Phillips • Medium and source dependent • Uses 2 first moments • Valid only in clear air atmosphere • Both require normalization of the moments United States Naval Academy Distribution A

  16. Gamma-Gamma and Gamma- Laguerre PDF of Field Data – above water * Histogram *Gamma-Gamma * Gamma-Laguerre occurrences Intensity, normalized United States Naval Academy Distribution A

  17. Gamma-Gamma and Gamma- Laguerre PDF of Field Data – above land * Histogram *Gamma-Gamma * Gamma-Laguerre occurrences Intensity, normalized United States Naval Academy Distribution A

  18. Gamma-Gamma and Gamma- Laguerre PDF of Field Data – at boundary * Histogram *Gamma-Gamma * Gamma-Laguerre occurrences Intensity, normalized United States Naval Academy Distribution A

  19. Gamma-Gamma and Gamma-Laguerre PDFs of irradiance – lab, no heat * Histogram *Gamma-Gamma * Gamma-Laguerre occurrences Intensity, normalized United States Naval Academy Distribution A

  20. Gamma-Gamma and Gamma-Laguerre PDFs of irradiance – Lab, phase screen * Histogram *Gamma-Gamma * Gamma-Laguerre occurrences Intensity, normalized United States Naval Academy Distribution A

  21. Summary • Gamma-Gamma and Gamma-Laguerrepdfs were developed using statistical moments from field and lab data • PDFs obtained from the field and the lab are very similar in appearance • Gamma-Laguerre fit the data better than Gamma-Gamma in the presence of scatterers in the field • Gamma-Laguerre was unstable at high values of due to numerical instabilities United States Naval Academy Distribution A

  22. Future Work • Better instrumentation for field data • Application of different mathematical models • Multi-resolution wavelet analysis • Coherence analysis independent of PDFs • Acknowledgements • Office of Naval Research United States Naval Academy Distribution A

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