Prof. A. Ziad
(S2, elective, 3 ECTS)
|Random fluctuations of physical parameters (temperature and wind speed) in the atmosphere cause fluctuations of the index of refraction of the air. This generates “optical turbulence”. When light propagates through the atmosphere, this optical turbulence turbulence is responsible for the degradation of image quality at the focus of telescope.
|Knowledge and Understanding:
|The main goal is to provide knowledge and skills in atmospheric optics, including the understanding of its fundamental laws, the theory of waves propagation & image formation through turbulent media, and the measurement of the main optical turbulence parameters.
|Applying Knowledge and Understanding:
|This course is not limited to astronomical observations. It is a very good basis for addressing the problems of light propagation in turbulent media such as Light horizontal propagation above the sea, Endoatmospheric observations, Fast imaging in industry through a turbulent medium, Satellites tracking, Optical Communications…
|Completed Fourier optics course Basic knowledge in mathematics (Fourier transforms, integrals, differential equations)
|Introduction to atmospheric turbulence and its impact on astronomical observations Observations in Astronomy, Loss of resolution Atmospheric turbulent layers (wavefront random deformations) Impacts of turbulence on High Angular Resolution (HAR) techniques
2. The atmospheric turbulence: Statistical properties, Dynamic and Optical Turbulence: Laminar and turbulent flows Characteristics of turbulent flows Origin of the turbulence The Kolmogorov’s theory: Energy cascade Dynamic turbulence Temperature fluctuations Refractive index fluctuations: Optical turbulence Turbulence localizing
3. Light propagation through the atmosphere: Phase structure function, turbulence models, scintillation & Angle of-arrival fluctuations: Light propagation through one turbulent layer Case of multiple layers (illustration with two layers) Structure function of phase fluctuations (Kolmogorov’s law) Spectral density of phase fluctuations Other models describing turbulence (von Karman, Greenwood-Tarazano)
4. Image formation through atmospheric turbulence Long exposure images Point spread function and optical transfer function of telescope & atmosphere Wavefront coherence (spatial, temporal, angular, chromatic) Wavefront coherence parameters
4. Site-testing instruments: Site selection Atmospheric turbulence characterization Turbulence profilers: Scidar, radio-sounding balloons, MASS, SLODAR, MOSP, PML. Turbulence monitors: DIMM, GSM, Scintillometer. Atmospheric turbulence and High Angular Resolution (HAR) techniques
|Description of how the course is conducted
|Lectures to acquire theoretical background on atmospheric turbulence and its origin, light propagation through turbulence, optical turbulence modelling & characterization, turbulence impacts on HAR techniques and site selection and testing,
On-sky observations with the Calern Atmospheric Turbulence Station (CATS).
Support and supervision of data processing, analysis and extraction of results on the atmospheric turbulence characterization by means of CATS instruments
|Description of the didactic methods
|Description of the evaluation methods
|Examination will be based on one report about the data processing and analysis of atmospheric turbulence measurements with dedicated instruments.
|The effects of Atmospheric Turbulence in Optical Astronomy by F. Roddier, Progress in Optics XIX, E. Wolf, 1981.