Multistar turbulence monitor: a new technique to measure optical turbulence profiles

Abstract

The strength and vertical distribution of atmospheric turbulence is a key factor determining the performance of optical and infrared telescopes, with and without adaptive optics. Yet, this remains challenging to measure. We describe a new technique using a sequence of short-exposure images of a star field, obtained with a small telescope. Differential motion between all pairs of star images is used to compute the structure functions of longitudinal and transverse wavefront tilt for a range of angular separations. These are compared with theoretical predictions of simple turbulence models by means of a Markov-Chain Monte-Carlo optimization. The method is able to estimate the turbulence profile in the lower atmosphere, the total and free-atmosphere seeing, and the outer scale. We present results of Monte-Carlo simulations used to verify the technique, and show some examples using data from the second AST3 telescope at Dome A in Antarctica.

PEPITO: atmospheric Profiling from short-Exposure focal Plane Images in seeing-limiTed mOde

“…Top: PSF aspect ratio, and bottom: FWHM for anisokinetism from a single atmospheric turbulence layer at one of four test altitudes. Varying layer strengths cause saturation and maximal elongation to different values.we get T /T0 = 0.1 for respectively a wind speed value of 30 m/s, which correspond to the limit presented by(Hickson et al 2019) to consider the finite exposure time as negligible in the seeing estimation. It coincides with our present results showing the estimates accuracy degradation up to 2 % for faster wind speed than 30 m/s.…”

“…their aspect ratio and Full Width at Half Maximum (FWHM) does not vary by accu-mulating more frames, which can be reached in tens of seconds to one minute regarding the seeing conditions. Recent external profiling experiments acquired the profile on-sky every 5 mn (Osborn et al 2018) and alternative approaches emerges that aim to increasing the temporal resolution to 2 mn (Hickson et al 2019). Considering the fact that we need 30 s-1 mn-long observation with PEPITO depending on the detector configuration, we may have a factor 4 improvement on the temporal resolution.. We present the concept of PEPITO in Sect.…”

Strobed Imaging as a Method for the Determination and Diagnosis of Local Seeing

“…A cruder version of this would entail offsetting the telescope, with the shutter open, between multiple strobes. One could extend this concept to multiple pinholes in the collimator focal plane along with multiple wedged apertures in its output pupil, which would allow one to do tomography as described in Hickson et al (2019);Beltramo-Martin et al (2019).…”

Night-time measurements of astronomical seeing at Dome A in Antarctica

“…In addition, Dome A is a natural laboratory for studies of the formation and dissipation of turbulence within the boundary layer. Future measurements of weather, seeing, and the low-altitude turbulence profile 27 , could contribute to a better understanding of the Antarctic atmosphere [28][29][30] The columns are the names of sites, the heights of towers for DIMMs, the 25th, 50th (median) and 75th percentile values of DIMM seeing, the median values of the FA seeing F A , intermediate seeing to large values (see Table 1).…”