Single star scidar: atmospheric parameters profiling using the simulated annealing algorithm

Abstract

In this paper, we present a new method to estimate, for each turbulent layer labelled i, the horizontal wind speed v(h i ), the standard deviation of the horizontal wind speed fluctuations σ v (h i ) and the integrated value of C 2 n over the thickness h i of the turbulent layer C 2 n (h i ) h i , where h i is the altitude of the turbulent layer. These parameters are extracted from single star scintillation spatiotemporal cross-correlation functions of atmospheric speckles obtained within the generalized mode. This method is based on the simulated annealing algorithm to find the optimal solution required to solve the problem. Astrophysics parameters for adaptive optics are also calculated using C 2 n (h i ) and v (h i ) values. The results of other techniques support this new method.

First single star scidar measurements at Dome C, Antarctica

“…To retrieve the respective vertical profiles of C 2 n (h), V(h) and σ v (h) (the variance of wind speed fluctuations at altitude h), we use a "Simulated Annealing" (SA) algorithm which is also described in Habib et al (2006). Here, we recall only that altitudes are sampled from 0 to 20 km, with a 1 km vertical resolution which is about the natural vertical resolution of the SSS.…”

“…Auto-correlations and cross-correlations between images separated by a temporal lag ΔT = 0, ΔT = 7 and 2ΔT = 14 ms are computed in real time and averaged over N ∼ 2000 images. In order to disentangle the broadening effect of the altitude and the wind velocity fluctuations during the time to process the N images, two cross-correlations are necessary (more details are found in Habib et al 2006). …”

“…To our knowledge, only the Scidar family, i.e.the double star scidar (Vernin & Azouit 1983b,a) and the single star scidar (Habib et al 2006) and the instrumented balloon (Azouit & Vernin 2005) are among these sound techniques. The Multi Aperture Scintillation Sensor (Kornilov et al 2003) or MASS, delivers C 2 N profiles along six slabs in the atmosphere, but it does not give access to ground turbulence nor the wind speed at any altitude.…”

Using stellar scintillation for studies of turbulence in the Earth’s atmosphere

“…Since the decorrelation due to velocity dispersion does not have the same effect on the enlargement of the autocorrelation as that due to altitude ( √ λh), the inversion is possible only if the cross-correlation is measured at various lags. The inversion is an ill-posed problem, which can be solved, for example, with the simulated annealing technique [85].…”

Interferential seeing monitor

“…This makes it possible to detect turbulence in lower turbulent layers (Fuchs et al 1998). The Single Star Scidar (Rocca et al 1990;Habib et al 2005Habib et al , 2006 was developed in order to use single star scintillation for the determination of the optical turbulence profiles. Based on these profiles, one can calculate the seeing as well as all other parameters for adaptive optics.…”