Home
About
Program
and Events
Post-Meeting
Publications
Gallery
Registration
Abstract
Submission
Location and Accommodation
Travel Info
Presenter
Resources
Science Oversight
Committee
Student/Travel
Support
Sponsors and Contributors
Contact
Us
MKWC
Home
Abstract Review

Corresponding Author
Name
Julien BORGNINO
Authors
NameAffiliation
Amokrane BERDJA LUAN - FACULTY OF SCIENCES - UNIVERSITY OF NICE SOPHIA
Jérôme MAIRE LUAN - FACULTY OF SCIENCES - UNIVERSITY OF NICE SOPHIA
Aziz ZIAD LUAN - FACULTY OF SCIENCES - UNIVERSITY OF NICE SOPHIA
Abstract
Session1 (Instrumentation and observations to quantify the magnitude and distribution of atmospheric optical turbulence.)
Title'An optical turbulence profiler for the terrestrial atmosphere boundary-layer'
AbstractThe statistical analysis of the angle-of-arrival(AA) fluctuations appears
to be well adapted to monitor the optical effects induced by atmospheric
turbulence on the images observed using ground-based telescopes. Observing stars, it is widely used in the case of nighttime observations. In daytime,these fluctuations may be observed on solar limb images at the telescope focus but also in the pupil plane using a technique identical
to a Foucault test.In this last case,the telescope pupil is observed through
a diaphragm (slit) with a width of a few seconds of arc placed on the image
of the solar limb. The AA fluctuations, considered according to the perpendicular to the solar limb, are thus transformed in intensity fluctuations. This is done at a first order approximation. A precise calibration must be performed. One can note here that this method is equivalent to the use of a Shack-Hartmann sensor, but with another spatial resolution. A special attention must be paid to the spatial and angular filtering associated with the use of the diaphragm on the solar limb. For the processing of the measurements this filtering will be taken into account. One can note that for nighttime experiments, the technique is the same observing the lunar limb. Some elements of discussion will be presented concerning the specificities of the use of the Sun or of the Moon like source.
The principle is described and the theory briefly summarized and illustrated by numerical simulations.This work leads to the presentation of a profiler
allowing to quantify and localize with a high altitude resolution the optical turbulence which degrades astronomical images.
At first, the observation of the intensity fluctuations (recorded using a CCD camera)in the image of the pupil through the diaphragm, therefore the AA fluctuations, makes easy the estimate of the wavefront spatial coherence parameters. For estimating the Fried parameter r0, the method is differential, like in the Differential Image Motion Monitor (D.I.M.M.) widely used to estimate the quality of astronomical images. The measurements of the structure functions corresponding to baselines between two sub-apertures parallel and perpendicular to the solar (lunar) edge allows to deduce estimates of r0.
The spatial coherence outer scale L0 may also be estimated using a distribution of sub-apertures on the pupil image analog to the one of the experiment G.S.M.(Generalized Seeing Monitor)which has allowed the evaluation of the major astronomical sites around the world. To have the same baselines that those of the standard G.S.M., it is necessary that the telescope diameter be at least equal to 1.5m. For smaller telescopes, another way could be the use of diaphragms of different sizes.This technique has been used in the past and the method has appeared notably robust.
Then, in order to obtain estimations of vertical profiles (of energy or turbulence outer scale) one can use a triangulation method observing two images of the telescope pupil through two diaphragms positioned at some angular distance on the solar (lunar) limb image. This experiment is identical to a SLODAR, the AA fluctuations being observed in the pupil image simultaneously for two angular directions in the sky, directions which can be easily selected like their angular separation. The possibility to choose this separation allows to hope, via a cross-correlation technique, a high vertical resolution. One can also consider that the AA fluctuations may be observed simultaneously for more than two directions in the sky (multiple objects for the SLODAR).For example, using 4 slits in non-redundant positions on the solar(lunar) limb images could lead simultaneously to 6 angular separations.
This study of the potentialities of the observation of the AA fluctuations in images of the telescope pupil using a technique identical to a Foucault test is done here in the context of the implementation of two other experiments.
The first one, is the Generalized Solar Seeing Monitor (M.I.Sol.F.A: Moniteur d'Images Solaires Franco-Algérien) which will be used for the comparison (in 2008) between solar diameter measurements performed from ground and space (PICARD mission (CNES)). It is based on simultaneous observations in the image and pupil planes of the AA fluctuations which leads, in the framework of a turbulence model, to the estimation of the coherence parameters characterizing the wavefronts. The optical turbulence profiles Cn2(h)will be also deduced. The objective is the modeling of the optical effects of atmospheric turbulence on ground measurements.
The other one, is the Monitor for Outer Scale Profile (M.O.S.P)which allows the estimate of the angular correlation of the AA fluctuations deduced from Moon's limb observations. The outer scale profiles L0(h) are generally estimated with given Cn2(h) profiles measured simultaneously with a SCIDAR.
Results have been recently obtained during two campaigns at the Mauna Kea Observatory and at the Haute Provence Observatory.
In the two cases, observations in the pupil plane should be performed in the future.

Return to Program and Events

Updated on: Wed, Dec 17 2014 - 1849 UTC
Send comments to: MKWC Staff