Frédéric Falzon

Satellite image restoration in the context of a spatially varying point spread function

In this paper, we consider a deconvolution problem where the point spread function (PSF) of the optical imaging system varies between different spatial locations, thus leading to a spatially varying blur. This problem arises, for example, in synthetic aperture instruments and in wide-field optical systems. Unlike the classical deconvolution context where the PSF is assumed to be spatially invariant, the problem cannot be easily solved in the Fourier domain. We propose here an iterative algorithm based on convex optimization techniques and a wavelet frame regularization. This approach allows restoration of the image, taking into account the properties of the blur operator, the latter being known.

Comparative theoretical and experimental study of a Shack-Hartmann and a Phase Diversity SENSOR, for high-precision wavefront sensing dedicated to Space Active Optics

Earth-imaging or Universe Science satellites are always in need of higher spatial resolutions, in order to discern finer and finer details in images. This means that every new generation of satellites must have a larger main mirror than the previous one, because of the diffraction. Since it allows the use of larger mirrors, active optics is presently studied for the next generation of satellites. To measure the aberrations of such an active telescope, the Shack-Hartmann (SH), and the phase-diversity (PD) are the two wavefront sensors (WFS) considered preferentially because they are able to work with an extended source like the Earths surface, as well as point sources like stars. The RASCASSE project was commissioned by the French spatial agency (CNES) to study the SH and PD sensors for high-performance wavefront sensing. It involved ONERA and Thales Alenia Space (TAS), and LAM. Papers by TAS and LAM on the same project are available in this conference, too [1,2]. The purpose of our work at ONERA was to explore what the best performance both wavefront sensors can achieve in a space optics context. So we first performed a theoretical study in order to identify the main sources of errors and quantify them — then we validated those results experimentally. The outline of this paper follows this approach: we first discuss phase diversity theoretical results, then Shack-Hartmann’s, then experimental results — to finally conclude on each sensor’s performance, and compare their weak and strong points.

Optical turbulence in confined media: part I, the indoor turbulence sensor instrument

Optical system performances can be affected by local optical turbulence created by its surrounding environment (telescope dome, clean room, atmospheric surface layer). We present our new instrument INdoor TurbulENce SEnsor (INTENSE) dedicated to this local optical turbulence characterization. INTENSE consists of using several parallel laser beams separated by non-redundant baselines between 0.05 and 2.5xa0m and measuring the angle of arrival fluctuations from spot displacements on a CCD. After introducing the theoretical background, we give a description of the instrument including a detailed characterization of instrumental noise and, finally, give the first results for the characterization of the turbulence inside clean rooms for optical systems studies.

Wave-front sensing for space active optics: Rascasse project

The payloads for Earth Observation and Universe Science are currently based on very stiff opto-mechanical structures with very tight tolerances. The introduction of active optics in such an instrument would relax the constraints on the thermo-mechanical architecture and on the mirrors polishing. A reduction of the global mass/cost of the telescope is therefore expected. Active optics is based on two key-components: the wave-front sensor and the wave-front corrector.

Optical turbulence in confined media. Part II:first results using the INTENSE instrument

Optical system performances can be affected by local optical turbulence created by its surrounding environment (telescope dome, clean room, or atmospheric layer). This paper follows a previous one introducing the INdoor TurbulENce SEnsor (INTENSE) instrument for optical turbulence characterization in a local area by exploitation of laser beam angle-of-arrival fluctuations. After a brief summary of the theoretical background, we present in this part results obtained using the INTENSE instrument in various optical integration testing clean rooms and telescope domes, each with specific air behavior conditions.

The INdoor turbulENce SEnsor (INTENSE) instrument

Optical system performances can be affected by local optical turbulence created by its surrounding environment (telescope dome, clean room, atmospheric surface layer). We present our new instrument INTENSE (INdoor TurbulENce SEnsor) dedicated to this local optical turbulence characterization. INTENSE consists of using several parallel laser beams separated by non-redundant baselines between 0.05 and 2.5m and measuring Angle-of-Arrival fluctuations from spots displacements on a CCD. We present detailed characterization of instrumental noise and first results for the characterization of the turbulence inside clean rooms for optical testing and integration.

The LAM space active optics facility

The next generation of large lightweight space telescopes will require the use of active optics systems to enhance the performance and increase the spatial resolution. Since almost 10 years now, LAM, CNES, THALES and ONERA conjugate their experience and efforts for the development of space active optics through the validation of key technological building blocks: correcting devices, metrology components and control strategies. This article presents the work done so far on active correcting mirrors and wave front sensing, as well as all the facilities implemented. The last part of this paper focuses on the merging of the MADRAS and RASCASSE test-set up. This unique combination will provide to the active optics community an automated, flexible and versatile facility able to feed and characterise space active optics components.