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SHIMM: a versatile seeing monitor for astronomy

Perera, Saavidra; Wilson, Richard W; Butterley, Tim; Osborn, James; Farley, Ollie JD; Laidlaw, Douglas J

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Saavidra Perera

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Ollie Farley
Post Doctoral Research Associate

Douglas J Laidlaw


Characterization of atmospheric optical turbulence is crucial for the design and operation of modern ground-based optical telescopes. In particular, the effective application of adaptive optics correction on large and extremely large telescopes relies on a detailed knowledge of the prevailing atmospheric conditions, including the vertical profile of the optical turbulence strength and the atmospheric coherence time-scale. The Differential Image Motion Monitor (DIMM) has been employed as a facility seeing monitor at many astronomical observing sites across the world for several decades, providing a reliable estimate of the seeing angle. Here, we present the Shack–Hartmann Image Motion Monitor (SHIMM), which is a development of the DIMM instrument, in that it exploits differential image motion measurements of bright target stars. However, the SHIMM employs a Shack–Hartmann wavefront sensor in place of the two-hole aperture mask utilized by the DIMM. This allows the SHIMM to provide an estimate of the seeing, unbiased by shot noise or scintillation effects. The SHIMM also produces a low-resolution (three-layer) measure of the vertical turbulence profile, as well as an estimate of the coherence time-scale. The SHIMM is designed as a low-cost, portable instrument. It is comprised of off-the-shelf components so that it is easy to duplicate and well suited for comparisons of atmospheric conditions within and between different observing sites. Here, the SHIMM design and methodology for estimating key atmospheric parameters will be presented, as well as initial field test results with comparisons to the Stereo-SCIntillation Detection And Ranging instrument.


Perera, S., Wilson, R. W., Butterley, T., Osborn, J., Farley, O. J., & Laidlaw, D. J. (2023). SHIMM: a versatile seeing monitor for astronomy. Monthly Notices of the Royal Astronomical Society, 520(4), 5475-5486.

Journal Article Type Article
Acceptance Date Jan 23, 2023
Online Publication Date Feb 13, 2023
Publication Date 2023-04
Deposit Date May 24, 2023
Publicly Available Date May 24, 2023
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 520
Issue 4
Pages 5475-5486
Public URL


Published Journal Article (2.6 Mb)

Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2023 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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