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Measuring Turbulence in Domes Jeff Fines University of Hawai‘i, Manoa - BSEE Craig Nance W.M. Keck Observatory 25 July 2008

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Overview Background Initial Tasks Redesign Deployment Obtained Data Conclusion 1

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Background Scintillation and Seeing –Turbulence Temperature Gradients Stirring Atmosphere In-Dome Seeing Displaced-Beam Small Aperture Scintillometer (DBSAS) –Structure Constant Goal –Summit Installation Feasible? Fig. 1: Astronomical Seeing Fig. 2: DBSAS 2

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Initial Work Unpack & Install –Familiarization DBSAS Set-Up –Point-to-point, 2- and 3-path –System Design Fig. 4: Basic System *not drawn to scale Fig. 3: Pathways TX RX 3

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Initial Deployment Unique Opportunity –2 nd Week Obtained Data –6:49pm - 9:18pm Observed Sensitivity of System –5.56∙10 -16 m -2/3 over 63 m path Rated Sensitivity of System –10 -16 m -2/3 over 100 m path 4 Fig. 5: Initial Configuration in Keck II Dome Fig. 6: Lowest Structure Constant Observed

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Technical Difficulties Measurement Snag –Cycled System –Checked Connections System Alignment –2 Person Requirement –SENSITIVE –Signal Strength Ch. 1 – Yellow Ch. 2 – Green 5 Fig. 7: System Alignment Fig. 8: Ideal strength for minimum error

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Redesign Easy Set-Up –More Compact Angle Correction New Cable –RS-485 Summit Simulation 6 Fig. 9: Before and After *not drawn to scale Fig. 10: Angle Compensation

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21 m

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Analyzing the Data 8 Day-Time Data –12:13pm – 3:20pm Observed Correlation –Inner Scale of Refractive Index Fluctuations –Small sample of data –“Suggested” Log Linear Relation Fig. 11: Structure Constant over Time Fig. 12a: Log Linear Relationship is “suggested” Fig. 12b: Correlation from first deployment

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Conclusion Robust System –Improved Reliability Appliance-Like Sensitive System –Calibration –Maintenance Installation is feasible –New Location –Trained Operator 9 Fig. 13: System on Cabinet

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Acknowledgements W.M. Keck Observatory Craig Nance Sarah Anderson Hualalai Warehouse Crew HQ Mechanical Shop Summit Crew Akamai Internship Program Lynne Raschke, Scott Seagroves, David Le Mignant Center for Adaptive Optics, NSF Grant Scintec Bettina Schrauf, Todd Reed TMT Tony Travouillon The Akamai Internship Program is funded by the Center for Adaptive Optics through its National Science Foundation Science and Technology Center grant (#AST-987683). 10

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Thank You

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Full-Width Half-Maximum (FWHM) FWHM = [ (C N 2 ∙H) / (6.8∙10 -13 ) ] 0.6 π Where C N 2 = Structure Constant H = Path Length π = the unit for arc sec a

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Conclusion Has Objective been fulfilled? Summarize findings. What is to come next for the DBSAS? 9

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Analyzing the Data **Description of graph. **What does it all mean?? 7 Rated Sensitivity of System: 10 -16 m -2/3 over 100 m path Observed Sensitivity of System: 5.56∙10 -16 m -2/3 over 63 m path Ratio of Rated to Observed: 1 to 8.825 Fig. 5: Initial Configuration

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