Do microthermals measure seeing?

Neville J. Woolf

doi:10.1117/12.19100

1 July 1990 Do microthermals measure seeing?

Neville J. Woolf

Proceedings Volume 1235, Instrumentation in Astronomy VII; (1990) https://doi.org/10.1117/12.19100
Event: SPIE Astronomical Telescopes and Instrumentation for the 21st Century, 1990, Tucson, AZ, United States

Abstract

Microthermals are often used to test for local seeing contributions of sites and inside telescope buildings. There is however a degree of uncertainty in their use. The refractive fluctuations are proportional to the air density fluctuations. But for isobaric changes the fractional air density fluctuations are equal to minus the fractional absolute temperature fluctuations. Whereas for adiabatic changes the fractional density changes are equal to plus 1/(Gamma4) times the absolute temperature fluctuation. The image size contributions are equal to these changes to the 1.2 power. Thus adiabatic changes produce about three times as much image degradation as do isobaric changes. There is a particular susceptibility to adiabatic changes with wave motion affecting seeing in the presence of stable stratification associated with a nocturnal ground thermal inversion. It is recommended that microthermal measures of seeing contribution from sites and telescope facilities should be treated with distrust unless accompanied by simultaneous measurements of pressure fluctuations. In consequence a number of current indicators for the thermal design of large telescopes and their facilities must be considered moot.

Citation Download Citation

Neville J. Woolf "Do microthermals measure seeing?", Proc. SPIE 1235, Instrumentation in Astronomy VII, (1 July 1990); https://doi.org/10.1117/12.19100

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available