Olivier Lai – Optimising image quality at the telescope: Altering reality to fit our simulations

Quand :
20 septembre 2022 @ 11 h 00 min – 12 h 00 min
2022-09-20T11:00:00+02:00
2022-09-20T12:00:00+02:00
Où :
B18N, Salle Univers

Speaker : Olivier Lai

Title: Optimising image quality at the telescope: Altering reality to fit our simulations

Self generated turbulence and dome seeing are starting to be recognised as strong contributors to the degradation of astronomical image quality, especially when using adaptive optics; besides the now infamous low wind effect, strange temporal power spectra, strong ground layer, low (temporal) frequency turbulence, high (spatial) frequency turbulence all point to local effects. Unfortunately accounting for and including all these sources of image degradation in our modelling seems intractable, because most of these effects are transient, stochastic and non-stationary, they all depend on too many environmental parameters to be causally interpreted (e.g. wind speed, direction, dome azimuth, heat sources, radiative cooling in the telescope structure and its (differential) thermal inertia, natural air temperature variations and partial venting).
It therefore seems useless, and on top of that very difficult, to estimate realistic AO performance from simulations that would try to incorporate all these effects. So instead of trying to align our simulations to reality, I propose that we try to align reality to our simulations. Indeed, we do not have to incorporate all these effects in our simulations: we can attempt to prevent them from occurring in the first place, and luckily all these local effects can be attenuated or averted at the source, using yet to be developed techniques such as intelligent dome design, cleverly positioned fans or precise real time thermal control including telescope structure heating. None of these are technologically challenging, but the control needs to be sensitive, active and real time, which requires an accurate sensing and mapping of the turbulence inside the telescope and dome.
In this talk, I will show some examples of intermittent turbulence related to environmental parameters on telescopes in Hawaii (CFTH, UH88), Arizona (LBT) and Antarctica (ASTEP), as a first step to implementing heuristic dome turbulence control.