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Optimum Laser PRF Study for Pulsed Wind Lidars M. J. Kavaya NASA Langley Research Center to

Optimum Laser PRF Study for Pulsed Wind Lidars M. J. Kavaya NASA Langley Research Center to Working Group on Space-Based Lidar Winds 8-9 Feb 2011. This is a notional presentation with many assumptions Please don’t place emphasis on exact numbers. 4 Different Cases Considered.

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Optimum Laser PRF Study for Pulsed Wind Lidars M. J. Kavaya NASA Langley Research Center to

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  1. Optimum Laser PRF Study for Pulsed Wind Lidars M. J. Kavaya NASA Langley Research Center to Working Group on Space-Based Lidar Winds 8-9 Feb 2011

  2. This is a notional presentation with many assumptions • Please don’t place emphasis on exact numbers

  3. 4 Different Cases Considered Coherent detection wind lidar, constant laser optical power Coherent detection wind lidar, constant laser wallplug power Direct detection wind lidar, constant laser optical power Direct detection wind lidar, constant laser wallplug power 5 Figures of Merit Wind measurement performance Laser design difficulty (optical power) Laser wallplug power Optical damage Computer speed and data rate

  4. Guess at Relative Importance of Figures of Merit

  5. Optimum Laser PRF fL (Energy = EL)Benefits and Costs W’s are weighting constants

  6. Cases 1 & 2. Coherent Detection Wind Lidar Constant Laser Optical Power & Constant Laser Wallplug Power

  7. Cases 1 & 2. Coherent Detection Wind Lidar Constant Laser Optical Power & Constant Laser Wallplug Power

  8. Cases 3 & 4. Direct Detection Wind Lidar Constant Laser Optical Power & Constant Laser Wallplug Power

  9. All 4 Formulae

  10. 9 Different Dependences on fL

  11. Parameter Values for Calculations *same as coherent due to ignorance of model value

  12. Equal Weightings, Performance x 100 • Optimum PRF: COH OPT < COH WP < DIR OPT < DIR WP • Coherent favors higher EL more than direct. • Wallplug power introduces efficiency, which favors higher PRF

  13. Equal Weightings, Performance x 100, Data x 5 • Higher data rate weight moved direct PRF down more than coherent

  14. Equal Weightings, Performance x 100

  15. Equal Weightings, Performance x 100, Damage x 100 • Large damage weight only slightly increases optimum PRF (hence slightly lower energy)

  16. Equal Weightings, Performance x 100

  17. Equal Weightings, Performance x 100, Laser Difficulty x 10 • Moderately weighting laser difficulty lowers optimum PRF for fixed wallplug power • Does not change optimum PRF for fixed optical power, as expected

  18. Equal Weightings, Performance x 100

  19. Equal Weightings, Performance x 100, Wallplug Power x 10 • Moderately weighting wallplug power greatly flattens PRF dependence of all cases • Terms with WPOW either independent of or gently depend on fL • Does not change optimum PRF for fixed wallplug power as expected

  20. Performance = Damage = 10,000. Data = 100. Others 0. • Broadest range of PRF = direct, constant WP. Narrowest = Coherent constant OP.

  21. Other Results • Increasing optical power increases optimum frequency for fixed optical power cases Conclusions • The optimum laser PRF may be different from the laser designer’s point of view, the lidar technique and measured geophysical parameter point of view, or the total space mission point of view? • The numbers herein should not be used, only the concepts

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