The technique of SCIDAR (SClintillation Detection And Ranging) was first suggested by Rocca et al[1] and has since been developed extensively by Vernin and colleagues[2],[3],[4],[5]. The idea is based upon two premises: (i) that the value of the refractive index structure constant C_n²(h) for a layer of turbulence at altitude h can be estimated from the variance of the scintillation received at the pupil of a telescope, and (ii) that layers can be identified using a triagulation technique based on recording the spatial correlation function of the scintillation from a double star of angular separation α, the height h of the layer being equivalent to the autocorrelation lag δx/α. Because the variance of the scintillation scales as h^5/3, it is not possible to measure C_n²(h) for h=0, i.e. in the pupil itself using SCIDAR. Recently, Fuchs et al [6] have extended the idea to the case where one records scintillation in a plane defocussed from the pupil plane, coining the term Generalised SCIDAR for this case, in which it is now possible to record C_n²(h) in the pupil. By measuring the spatio-temporal correlation for light from a single star, the velocities of the dominant layers can also be estimated.

Date Published: 1 September 1996
PDF: 2 pages
Proc. SPIE 2778, 17th Congress of the International Commission for Optics: Optics for Science and New Technology, 2778D9 (1 September 1996); doi: 10.1117/12.2316166

Published in SPIE Proceedings Vol. 2778:
17th Congress of the International Commission for Optics: Optics for Science and New Technology
Joon-Sung Chang; Jai-Hyung Lee; ChangHee Nam, Editor(s)