measuring turbulence in domes jeff fines university of hawai‘i, manoa - bsee craig nance w.m. keck...
TRANSCRIPT
Measuring Turbulence in Domes
Jeff FinesUniversity of Hawai‘i, Manoa - BSEE
Craig NanceW.M. Keck Observatory
25 July 2008
Overview
•Background•Initial Tasks•Redesign•Deployment•Obtained Data•Conclusion
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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
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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
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Initial Deployment
•Unique Opportunity–2nd 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
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Fig. 5: Initial Configuration in Keck II Dome
Fig. 6: Lowest Structure Constant Observed
Technical Difficulties
•Measurement Snag–Cycled System–Checked Connections
•System Alignment–2 Person Requirement–SENSITIVE–Signal Strength
•Ch. 1 – Yellow•Ch. 2 – Green
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Fig. 7: System Alignment
Fig. 8: Ideal strength for minimum error
Redesign
•Easy Set-Up–More Compact
•Angle Correction•New Cable
–RS-485
•Summit Simulation
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Fig. 9: Before and After *not drawn to scale
Fig. 10: Angle Compensation
21 m
Analyzing the Data
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•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 TimeFig. 12a: Log Linear Relationship is “suggested”Fig. 12b: Correlation from first deployment
Conclusion
•Robust System–Improved Reliability
•Appliance-Like•Sensitive System
–Calibration–Maintenance
•Installation is feasible
–New Location–Trained Operator
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Fig. 13: System on Cabinet
AcknowledgementsW.M. Keck Observatory
Craig NanceSarah Anderson
Hualalai Warehouse CrewHQ Mechanical Shop
Summit Crew
Akamai Internship ProgramLynne Raschke, Scott Seagroves, David Le Mignant
Center for Adaptive Optics, NSF Grant
ScintecBettina Schrauf, Todd Reed
TMTTony 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).
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Thank You
Full-Width Half-Maximum (FWHM)
FWHM = [ (CN2∙H) / (6.8∙10-
13) ]0.6 π
Where • CN
2 = Structure Constant• H = Path Length• π = the unit for arc sec
a
Conclusion
•Has Objective been fulfilled?•Summarize findings.•What is to come next for the DBSAS?
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Analyzing the Data
•**Description of graph.•**What does it all mean??
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Rated Sensitivity of System: 10-16 m-2/3 over 100 m pathObserved Sensitivity of System: 5.56∙10-16 m-2/3 over 63 m pathRatio of Rated to Observed:
1 to 8.825
Fig. 5: Initial Configuration