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Dome Turbulence

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  • Centre for Advanced Instrumentation
    Department of Physics
    University of Durham
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    DH1 3LE

Dome Turbulence

Sequence of the measured dome turbulence at the OGS for the night of 20/09/2022. The data shows very strong turbulence early in the night which drops until approximately local midnight. No effort was made to minimise the dome turbulence during this campaign. Results are still preliminary pending rigorous review and analysis.  

Optical turbulence in the enclosure of a ground-based telescope can be a major contributor to the total turbulence strength and can therefore limit observational precision in terms of angular resolution, or signal to noise ratio, depending on the instrumentation used.

Here we propose a new dome turbulence monitor technique: Scintillation based Dome turbulence monitor (SciDome). SciDome is based on the well known SCIDAR concept with a few major differences. By designing the instrument specifically for the done turbulence, we can use a small (<0.2~m telescope), and observe single bright stars (rather than doubles). This enables a dedicated instrument capable of pointing anywhere in the sky.

Operationally, SciDome could be mounted somewhere on the master telescope / dome structure and track stars that are visible through the dome aperture. By measuring through the dome aperture we obtain an optical measure of the strength of the turbulence along the same line of sight as the master telescope itself.

We demonstrate the new technique through numerical Monte-Carlo modelling and present results from a proof-of-concept demonstration at the European Space Agency Optical Ground Station on Tenerife, Spain.

Average conjugated image to +450 m from measured data. Left is instantaneous image and right is average image.
Example spatio-temporal co-variance function. The green circle indicates the signal due to the dome turbulence, constrained in the centre of the function. The other layer is the high-altitude turbulence layer which moves through the co-variance function with the velocity of the translational wind (from bottom to top).
Scintillation co-variance as a function of temporal delay. A linear fit is used to extrapolate to zero temporal delay in order to estimate the scintillation co-variance due to the dome turbulence. The red and green dashed lines indicate the linear fit in the forward and backward temporal direction.
Expected sensitivity to dome turbulence. As expected from simulation, the response is linear down to ~10^{-14}, which is the noise floor of the current system. This could be improved with a larger telescope but actually weak dome turbulence is of less importance than strong turbulence and so this is sufficient for most applications.