Exposure-Time Effects on Differential r0 Measurements

Soules, David B.; Drexler, J.; Draayer, Bret F.; Eaton, Frank D.; Hines, John R.

doi:10.1086/133801

Cited by 13 publications

(10 citation statements)

References 15 publications

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“…Thus if we denote the temporal fluctuation of the image displacement from a pupil at a location as and the spatial fluctuation of the wavefront tilt (angle of arrival) as , the relation holds, where t is time and is the wind velocity. Note that this could be a valid assumption when the exposure time is sufficiently short (Soules et al 1996).…”

Section: Methods To Convert Data From a Dimm To Fried’s Parametermentioning

confidence: 99%

Seeing measurements using the solar limb - I. Comparison of evaluation methods for the Differential Image Motion Monitor

Kawate

Hanaoka

Ichimoto

et al. 2011

Monthly Notices of the Royal Astronomical Society

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Differential Image Motion Monitors (DIMMs) are used not only for stellar observations but also for solar observations with the limb as the target to evaluate the seeing. In stellar observations, the differential image motions along and perpendicular to the DIMM baseline are consistently employed to evaluate Fried’s parameter. However this is not the case for solar‐limb observations, in which we can measure the image motion only perpendicular to the limb. Therefore the validity of the methods so far proposed to calculate Fried’s parameter from a DIMM using the solar limb is still open to examination. We have focused on this problem and carried out DIMM observations of the solar limb using a Shack–Hartmann wavefront sensor of the Domeless Solar Telescope at Hida Observatory. Pairs of apertures in the Shack–Hartmann sensor act as multiple DIMMs that have different baselines in distance and orientation. We calculated Fried’s parameters based on three evaluating methods (those of Sarazin & Roddier, Sasiela and Conan et al.) and found that the method of Sarazin & Roddier gives a consistent value of Fried’s parameter over the set of multiple DIMMs.

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Section: Methods To Convert Data From a Dimm To Fried’s Parametermentioning

confidence: 99%

Seeing measurements using the solar limb - I. Comparison of evaluation methods for the Differential Image Motion Monitor

Kawate

Hanaoka

Ichimoto

et al. 2011

Monthly Notices of the Royal Astronomical Society

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“…We recall that in Martin (1987) and Soules et al (1996), the wind correction was estimated on the basis of model assumptions about the vertical OT profile C 2 n ( h ) and wind speed v ( h ). Estimations of this kind are useful for planning or analysis but are not suitable for the reduction of real data because of their low accuracy.…”

Section: Effect Of the Whole Atmospherementioning

confidence: 99%

“…The need to reduce this effect has led to the appearance of both theoretical (Martin 1987) and experimental (Soules et al 1996) studies of the impact of exposure on the power of differential image motion measured with the DIMM. The methods of correction developed by Martin (1987) and Soules et al (1996) require a priori information about the wind or some temporal characteristics of the image motion estimated during the measurement process. For this reason, the DIMM data are usually corrected for this bias using interlaced exposures.…”

Section: Introductionmentioning

confidence: 99%

Differential image motion in the short-exposure regime

Kornilov¹,

Safonov²

2011

Monthly Notices of the Royal Astronomical Society

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The seeing β 0 over the whole atmosphere is the most important characteristic for site-testing measurements. The estimation of the seeing using the variance of differential image motion is always biased by wind smoothing because of non-zero exposure of the differential image motion monitor (DIMM). This results in wind smoothing. In this paper, we study the wind effects within a short-exposure approximation (i.e. when the wind shifts the turbulence during exposure by a distance less than the device aperture). We propose a method for correcting this effect, based on the correlation of image motion between the adjacent frames. We show that the correlation can be used to estimate the mean wind speedV 2 and the atmospheric coherence time τ 0 . We suggest using the total power of the longitudinal and transverse image motion to eliminate the dependence on wind direction. The theoretical results obtained have been tested on data gathered at Mount Shatdzatmaz during 2007-2010 using the DIMM combined with multi-aperture scintillation sensor (MASS). Good agreement was found.

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“…This effect becomes apparent for strong winds in the boundary layer, where the main part of the turbulence is usually located, and at high altitudes with wind streams of 25–40 m s −1 . It is common to use a double‐exposure method when frames of single and double exposures are interlaced, and a certain extrapolation (Tokovinin 2002a) is exploited to obtain a ‘zero‐exposure’ variance estimation based on theoretical considerations (Martin 1987; Soules et al 1996).…”

Section: Ot‐measurement Data Reductionmentioning

confidence: 99%

First results of a site-testing programme at Mount Shatdzhatmaz during 2007-2009

Kornilov¹,

Shatsky²,

Voziakova³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We present the first results of site testing performed at Mt Shatdzhatmaz in the Northern Caucasus, where the new Sternberg Astronomical Institute 2.5-m telescope will be installed. An automatic site-monitor instrumentation and functionality are described, together with the methods of measurement of the basic astroclimate and weather parameters. The clear night-sky time derived on the basis of 2006-2009 data amounts to 1340 h per year.Principal attention is given to measurement of the optical-turbulence altitude distribution, which is the most important characteristic affecting the performance of optical telescopes. For the period from more than 85 000 turbulence profiles were collected using the combined Multi Aperture Scintillation Sensor and Differential Image Motion Monitor (MASS/DIMM) instrument. The statistical properties of the turbulent atmosphere above the summit are derived and the median values for seeing β 0 = 0.93 arcsec and free-atmosphere seeing β free = 0.51 arcsec are determined. Together with the estimations of isoplanatic angle θ 0 = 2.07 arcsec and time constant τ 0 = 2.58 ms, these are the first representative results obtained for Russian sites, and are necessary for the development of modern astronomical observation techniques like adaptive optics.

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Exposure-Time Effects on Differential r0 Measurements

Cited by 13 publications

References 15 publications

Seeing measurements using the solar limb - I. Comparison of evaluation methods for the Differential Image Motion Monitor

Seeing measurements using the solar limb - I. Comparison of evaluation methods for the Differential Image Motion Monitor

Differential image motion in the short-exposure regime

First results of a site-testing programme at Mount Shatdzhatmaz during 2007-2009

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