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

1

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

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

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

6

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

9

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