Lectura de tesi: "Study of adaptative optics images by means multiscalar transforms"

  • Autor/Doctorand: Roberto Baena Gallé.
  • Dia: Dilluns, 09 de desembre de 2013
  • Hora: 11:30
  • Lloc: Sala de Graus (aulari)
  • Tribunal:​
    • President: Dr.   XAVIER LURI CARRASCOSO 
    • Secretari: Dr.   XAVIER OTAZU PORTER
    • Vocal: Dr.   SZYMON GLADYSZ     
  • Directors/Tutors: Dr.    JORGE NUÑEZ DE MURGA
  • Resum:

Adaptive optics (AO) systems are used to increase the spatial resolution achieved by ground-based telescopes, which are limited by the atmospheric motion. Therefore, the real cut-off frequency is extended closer to the theoretical diffraction limit thus allowing more high-frequency information to be present in the image. Nevertheless, although the goal of deconvolution algorithms is basically the same, and since the correction of AO is not complete, the simultaneous use of such deconvolution algorithms over AO dataset is desirable. On the other hand, multiresolution tools like the wavelet transform (WT) have been historically introduced into deconvolution schemes improving their performance with respect to their non-wavelet counterparts. 

This thesis investigates the application of multiresolution transform in AO imaging. Firstly, the algorithm AWMLE is applied over binary systems simulated for the 3-m Shane telescope to evaluate the photometric accuracy of the reconstructions. Its performance is compared with algorithms that are commonly used by the AO community. Results show that AWMLE is able to produce similar, if not better, results with respect to the rest of codes, especially for high Strehl ratios (SR) and matched PSFs. Secondly, a new deconvolution algorithm called ACMLE, based on the curvelet transform, is designed for the reconstruction of extended objects. ACMLE is tested together with AMWLE and blind/myopic codes over Saturn and galaxy simulated images for the 5-m. Hale telescope. The performance in the presence of noise of the multiresolution static-PSF algorithms is better than myopic and blind algorithms, thus showing the control of noise is as important as the update of the PSF estimate during the reconstruction process. In a third place, the 1D-WT is applied in the spectral deconvolution of integral field spectroscopy (IFS) datacubes for direct imaging of exoplanets with EPICS instrument, which will be installed at the  39-m E-ELT telescope. An improvement of 1 mag from angle separations equal to 73 mas is devised. Detection of close-in planets also benefit of the application of wavelets. The use of WT allows the APLC chronograph to obtain similar results with respect to the apodizer-only solution thus showing that WT classify planet frequency components and chromatic aberrations at different scales. 
This thesis opens several lines of research that will be addressed in future. Firstly, the world of multiresolution transforms is extremely huge and has produced dozens of new mathematical tools. Among many other, we mention the shearlet transform and the waveatom tool. They should be studied to establish their best performance and field of application over AO images. Secondly, blind and myopic algorithms have proved their ability for large mismatches between the “real” PSF and the PSF that is used as a first estimate. However, their performance in the presence of noise is highly affected. Hence, it is convenient to investigate how to introduce multiresolution analysis into these algorithms to improve their behavior. Finally, for the study of IFS datacubes, other father scaling functions with different shapes can be proposed. Besides, the design of a dictionary of wavelets, which increase the decomposing resolution across the spaxel can improve the photometric accuracy as well as the spectral characterization.



Dimarts, 3 Desembre, 2013