Optical turbulence profiling at Mount John University Observatory

Mohr, J. J.; Johnston, Rachel A.; Worley, C. C.; Cottrell, P. L.

doi:10.1117/12.799756

Cited by 4 publications

(3 citation statements)

References 10 publications

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“…As Δt increases further, the strength of the remaining secondary peak will exceed that of the central peak [12]. Figure 8 shows the resulting comparative strengths of the central and secondary peaks of a simulated 5km layer as Δt is increased between cross-correlation frames.…”

Section: Partial Triplet Analysismentioning

confidence: 95%

Detection of wind velocities from scintillation images

Mohr

Johnston

Cottrell

2008

2008 23rd International Conference Image and Vision Computing New Zealand

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SCIDAR (SCIntillation Detection And Ranging) has been used at various sites around the world to characterise turbulence strength. However little focus has been given to finding average wind velocity, V (h), from SCIDAR data. Current methods rely on the detection of full spatio-temporal covariance profiles, containing a triplet pattern associated with each turbulent layer present. A new technique for finding V (h) from noisy scintillation covariance images using a modified CLEAN algorithm has been developed to handle partial spatio-temporal covariance profiles. The application of the new algorithm to data collected from Mount John University Observatory is demonstrated.

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Section: Partial Triplet Analysismentioning

confidence: 95%

Detection of wind velocities from scintillation images

Mohr

Johnston

Cottrell

2008

2008 23rd International Conference Image and Vision Computing New Zealand

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“…The University of Canterbury SCIDAR system (UC-SCIDAR) is a purpose-built instrument designed to measure C N 2 (h) and V(h) profiles (Johnston et al 2004(Johnston et al , 2005Mohr et al 2006Mohr et al , 2008aMohr et al , 2008b. UC-SCIDAR saw first light on the McLellan 1-m telescope at MJUO in late 2003, at an approximate cost of USD$4000.…”

Section: Measuring Turbulencementioning

confidence: 99%

“…The UC-SCIDAR system used in 2005 captured data at a frame rate of 30 Hz, which limits the maximum detectable velocity on a 1-m telescope to 30 m s À1 under ideal conditions (Mohr et al 2008b). This was a limitation of the CCD cameras used at the time.…”

Section: Optical Turbulence Measurements and Models For Mount John Unmentioning

confidence: 99%

Optical Turbulence Measurements and Models for Mount John University Observatory

Mohr¹,

Johnston²,

Cottrell³

2010

Publ. – Astron. Soc. Aust

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Site measurements were collected at Mount John University Observatory in 2005 and 2007 using a purpose-built scintillation detection and ranging system. C N 2 (h) profiling indicates a weak layer located at 12-14 km above sea level and strong low altitude turbulence extending up to 5 km. During calm weather conditions, an additional layer was detected at 6-8 km above sea level. V(h) profiling suggests that tropopause layer velocities are nominally 12-30 m s À1 , and near-ground velocities range between 2 and 20 m s À1 , dependent on weather. Little seasonal variation was detected in either C N 2 (h) and V(h) profiles. The average coherence length, r 0 , was found to be 7 AE 1 cm for the full profile at a wavelength of 589 nm. The average isoplanatic angle, y 0 , was 1.0 AE 0.1 arcsec. The mean turbulence altitude, h 0 , was found to be 2.0 AE 0.7 km above sea level. No average in the Greenwood frequency, f G , could be established due to the gaps present in the V(h) profiles obtained. A modified Hufnagel-Valley model was developed to describe the C N 2 (h) profiles at Mount John, which estimates r 0 at 6 cm and y 0 at 0.9 arcsec. A series of V(h) models were developed, based on the Greenwood wind model with an additional peak located at low altitudes. Using the C N 2 (h) model and the suggested V(h) model for moderate ground wind speeds, f G is estimated at 79 Hz.

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Multiscale optimization of the geometric wavefront sensor

et al. 2021

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Since wavefront distortions cannot be directly measured from an image, a wavefront sensor (WFS) can use intensity variations from a point source to estimate slope or curvature of a wavefront. However, processing of measured aberration data from WFSs is computationally intensive, and this is a challenge for real-time image restoration or correction. A multi-resolutional method, known as the ridgelet transform, is explored to estimate wavefront distortions from astronomical images of natural source beacons (stars). Like the curvature sensor, the geometric WFS is relatively simple to implement but computationally more complex. The geometric WFS is extended by incorporating the sparse and multi-scale geometry of ridgelets, which are analyzed to optimize the performance of the geometric WFS. Ridgelets provide lower wavefront errors, in terms of root mean square error, specifically over low photon flux levels. The simulation results further show that by replacing the Radon transform of the geometric WFS with the ridgelet transform, computational complexity is reduced.

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Optical turbulence profiling at Mount John University Observatory

Cited by 4 publications

References 10 publications

Detection of wind velocities from scintillation images

Detection of wind velocities from scintillation images

Optical Turbulence Measurements and Models for Mount John University Observatory

Multiscale optimization of the geometric wavefront sensor

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