Instrumentation
The group leads the design phase of the European Solar Telescope (EST) in close collaboration with several european institutions.
European Solar Telescope: Progress status
In this paper, the present status of the development of the design of the European Solar Telescope is described. The telescope is devised to have the best possible angular resolution and polarimetric performance, maximizing the throughput of the whole system. To that aim, adaptive optics and multi-conjugate adaptive optics are integrated in the optical path. The system will have the possibility to correct for the diurnal variation of the distance to the turbulence layers, by using several deformable mirrors, conjugated at different heights. The present optical design of the telescope distributes the optical elements along the optical path in such a way that the instrumental polarization induced by the telescope is minimized and independent of the solar elevation and azimuth. This property represents a large advantage for polarimetric measurements. The ensemble of instruments that are planned is also presented.
Light distribution system. Dichroic beam-splitters are indicated with squares and intensity beam-splitters with inclined lines crossing the light beam. The numbers at the side of the latter indicate approximate reflection/transmission percentages for an adequate illumination of all channels.
Compressive sensing for spectroscopy and polarimetry
We demonstrate, through numerical simulations with real data, the feasibility of using compressive sensing techniques for the acquisition of spectro-polarimetric data. This allows us to combine the measurement and the compression process into one consistent framework. Signals are recovered using a sparse reconstruction scheme from projections of the signal of interest onto appropriately chosen vectors, typically noise-like vectors. The compressibility properties of spectral lines are analyzed in detail. The results shown in this paper demonstrate that, thanks to the compressibility properties of spectral lines, it is feasible to reconstruct the signals using only a small fraction of the information that is measured nowadays. We investigate in depth the quality of the reconstruction as a function of the amount of data measured and the influence of noise. This change of paradigm also allows us to define new instrumental strategies and to propose modifications to existing instruments in order to take advantage of compressive sensing techniques.
Example showing how reliable reconstructions of high-resolution signals can be obtained from rebinned data, provided that the signal is considered to be compressible. The upper panel shows the original (black) and reconstructed profiles using 1/2 (red) and 1/4 (blue) of the original resolution. The data is reconstructed with 5 PCA eigenvectors of a universal basis set. The lower panel shows the measurements from which the reconstructions are obtained. The original signal is shown in black, while red and blue lines show measurements rebinned to 1/2 and 1/4 of the original resolution.