MICADO – First Light Instruments for the European Extremely Large Telescope (E-ELT)

by Roland Wagner, RICAM

Apart from METIS, our group in Linz is also involved in the development of MICADO, the Multi-AO Imaging Camera for Deep Observations of the E-ELT. The consortium behind MICADO is led by the Max Planck Institute for Extraterrestrial Physics  (MPE).

What is MICADO?
The name MICADO is well-known in a slightly different spelling, Mikado, as a pick-up sticks game. Within the European ELT, MICADO is an imaging instrument focusing on high presicion astrometry and spectroscopy. Optimised for imaging at the diffraction limit in H, J and K band (0.8-2.4 microns) with high angular resolution, MICADO will allow discovery and study of new or unexplored phenomena, such as the detailed structure of galaxies at high redshift, the study of individual stars in nearby galaxies and exoplanets.

Estimating the blur of observed Images
MICADO will, as a modern instrument, be equipped with an Adaptive Optics System to obtain comparable or even superior image quality to the American James Webb Space Telescope. However, using Adaptive Optics does not fully resolve deficiencies introduced by atmospheric turbulence, especially due to a time lag and limited resolution of the Wavefront Sensors (WFS) in the system.
As a consequence, the observed image appears blurred, but the effect of blurring, described by the point spread function (PSF), can be estimated from AO data. The PSF depends on the geometry of the telescope and the residual wavefront aberrations after AO correction.

psf_xao_without_ao

Point spread function without an AO System Credit: Iuliia Shatokhina

 

psf_xao_with_ao

Point spread function with an AO System. The more “delta-peak-like”, the better. Credit: Iuliia Shatokhina

An additional drawback of using AO systems is that the PSF varies with the position in the image, as the correction is performed along specified directions. Thus, spatially varying estimates for the PSF are needed. We improve existing and develope new algorithms to obtain accurate PSF estimates.
In the following Images (just for illustration purposes), we show how an image of stars is blurred through observation with a ground based telescope with AO correction.

 

stars_unblurred

True image of a star. Credit: Kirk Soodhalter.

 

stars_blurred

Blurred Image. Credit: Kirk Soodhalter

 

 

Improving images in a postprocessing step
The PSF of an observation does not only serve as a quality measure for the AO correction, but it can also be used for image improvement in a post-observational procedure. Mathematically speaking, a convolution of the true image and the PSF gives the observed image. Thus, having an estimate for the PSF, the observed image can be improved by using a deconvolution algorithm. Due to effects related to the AO system, the estimate for the PSF might not be accurate enough for directly improving the observed image by deconvolution. We are now developing blind deconvolution algorithms, allowing for changes in the PSF and taking care of specific available information on the observed stars. This will result in images where very faint stars up to magnitude 30 can be detected.

stars_reconstructed

The effect of deconvolution is learly visible. Credit. Kirk Soodhalter.

In a second step MICADO will be coupled to MAORY, the Multi-conjugate Adaptive Optics RelaY  for the E-ELT, which will provide a more uniform correction over the field of view and make use of atmospheric tomography as described in a former blog post

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