High resolution earth observation from geostationary orbit by optical aperture synthesys

Abstract

In this paper, we describe Optical Aperture Synthesis (OAS) imaging instrument concepts studied by Alcatel Alenia Space under a CNES R&T contract in term of technical feasibility. First, the methodology to select the aperture configuration is proposed, based on the definition and quantification of image quality criteria adapted to an OAS instrument for direct imaging of extended objects. The following section presents, for each interferometer type (Michelson and Fizeau), the corresponding optical configurations compatible with a large field of view from GEO orbit. These optical concepts take into account the constraints imposed by the foreseen resolution and the implementation of the co-phasing functions. The fourth section is dedicated to the analysis of the co-phasing methodologies, from the configuration deployment to the fine stabilization during observation. Finally, we present a trade-off analysis allowing to select the concept wrt mission specification and constraints related to instrument accommodation under launcher shroud and in-orbit deployment.

Relative Dynamics and Control of Satellite Formation Flying Representing the Synthetic Aperture Telescope on Geostationary Orbit

“…In this paper, to cover the largest possible area and provide high temporal and spatial resolution, it is proposed to use a satellite formation flying at GEO and representing a synthetic aperture telescope in the form of a Fizeau interferometer that provides a high spatial resolution corresponding to the resolution of an individual telescope with a high quality optical system [1]. The use of multi-aperture telescope makes it possible to obtain a high quality image of the Earth's surface with the help of 3 and more satellites representing its optical elements [2][3][4][5][6][7][8].…”

Large amplitude tip/tilt estimation by geometric diversity for multiple-aperture telescopes

“…So far, this technique has been operational only on groundbased telescopes, but interferometers have long been forecast for high-resolution spaceborne astronomy, for the soon-to-belaunched James Webb Space Telescope (JWST) [9] or other projects [10][11][12][13], and for Earth observation [14,15].…”

Numerical line of sight stabilisation for high resolution earth observation from high orbits

“…An example of optical design is presented in the Fig. 8 of [4]. In order to get a global image translation, the FSM is placed on the real exit pupil.…”

“…Accordingly, multi-pupils instruments have been studied in order to make such missions feasible. Different instrument concepts based on Optical Aperture Synthesis (OAS) have been proposed ( [2], [4], [5]) and, in this paper we mainly focus on the OAS 1,2 meter resolution Geo imaging instrument consisting of nine 1,8 m diameter pupils as described in [4]. As a comparison, we also consider the -unfeasible -16 m diameter monolithic instrument that was used as an Image Quality (IQ) reference in this study.…”