MicroCarb is a space mission designed to monitor the CO2 fluxes at the earth surface in order to better understand exchanges between atmosphere, oceans and vegetation. The specificity of Microcarb is its capacity to measure very precisely the CO2 atmospheric concentration (better than 1ppm) using a microsatellite (180kg). The MicroCarb mission is developed by the French Space Agency CNES through a funding from French Research Agency ANR and with participations from European Union and UK Space Agency. The Microcarb payload is composed of a passive Short Wave InfraRed spectrometer and a visible imager. The innovative concept of the spectrometer allows to acquire 4 narrow bands (0.76μm, 1.27μm, 1.61μm, 2.04μm) on a same detector thanks to the use of an echelle grating and a split-pupil telescope. The performances required for the instrument are very stringent in terms of spectral resolution (R~25000), Instrument Spectral Response Function (ISRF) knowledge (<1%), radiometry and polarization’s sensitivity (~ 0.3%). To achieve such high performances, on ground and in flight spectrometer calibration is a key point for the success of the mission. The payload is developed by Airbus Defence and Space (ADS) France and the assembly phase is now almost complete. First performance results in ambient conditions were obtained with a calibration detector and were in line with the expected values. The instrument activities will continue with the mechanical qualification and Thermal VACuum (TVAC) tests during which all the instrument performances will be measured. Delivery of the instrument is scheduled today at autumn 2022 for further integration on platform. This paper will focus on the technical overview of the instrument and on its critical performances. Then we will present the calibration philosophy and the first tests results.
Able to monitor very precisely CO2 gases concentration in the atmosphere (better than 1 ppm), MicroCarb is a CNES mission which instrument is a passive Short Wave InfraRed spectrometer that will help scientists to better understand the planet’s major ecosystems and gain a clearer picture of its carbon budget at regional scales. Reaching such a monitoring precision means that the instrument has very stringent requirements especially in terms of radiometry, spectral filtering, spectral bands co-registration and polarization sensitivity. The MicroCarb instrument is currently under integration at Airbus Defence and Space facilities in Toulouse (France). It is based on an innovative concept permitting the acquisition of the spectral bands using a single split-pupil telescope, spectrometer and detector. Spectral bands multiplexing is obtained by the grating, each band corresponding to a different diffraction order, between 15 and 40. The split-pupil concept is characterized by 3 sets of 4 to 5 assembled prisms at entrance telescope pupil, spectrometer slit and in front of the detector, all participating to the complex spectral filtering. All the components considered as critical for the performances of the instrument have been manufactured and are under integration: the echelle grating replicated in a SiC substrate, the assembled optical elements with narrow spectral filtering coatings and the Dual Babinet polarization scrambler. In this paper we will focus on these optical components, detailing for each one how the stringent requirements of the instrument have been transposed to their specification, close to the limits of manufacturability. We will be able to present their development and achievement with respect to these specifications and how they impact the global performances of the instrument.
The future generation of high angular resolution space telescopes will require breakthrough technologies to combine large diameters and large focal plane arrays with compactness and lightweight mirrors and structures. Considering the allocated volume medium-size launchers, short focal lengths are mandatory, implying complex optical relays to obtain diffraction limited images on large focal planes.
In this paper we present preliminary studies to obtain compact focal plane arrays (FPA) for earth observations on low earth orbits at high angular resolution. Based on the principle of image slicers, we present an optical concept to arrange a 1D FPA into a 2D FPA, allowing the use of 2D detector matrices. This solution is particularly attractive for IR imaging requiring a cryostat, which volume could be considerably reduced as well as the relay optics complexity.
Enabling the use of 2D matrices for such an application offers new possibilities. Recent developments on curved FPA allows optimization without concerns on the field curvature. This innovative approach also reduces the complexity of the telescope optical combination, specifically for fast telescopes. This paper will describe the concept and optical design of an F/5 - 1.5m telescope equipped with such a FPA, the performances and the impact on the system with a comparison with an equivalent 1.5m wide field Korsch telescope.
The emergence of curved detectors, first proposed by Ko et al in their Nature paper [1], certainly represents the major disruptive technology for imaging systems that will come up in a near future.
LAM and CEA-LETI are developing the technology of deformable detectors, for UV, VIS or NIR applications. Such breakthrough devices will be a revolution for future wide field imagers and spectrographs, firstly by improving the image quality with better off-axis sharpness, resolution, brightness while scaling down the optical system, secondly by overcoming the manufacturing issues identified so far and by offering a flexibility and versatility in optical design. The technology of curved detectors can benefit of the developments of active and deformable structures, to provide a flexibility and a fine tuning of the detectors curvature by thinning down the substrate without modifying the fabrication process of the active pixels. We present studies done so far on optical design improvements, the technological demonstrators we developed and their performances as well as the future five-years roadmap for these developments.
InfraRed (IR) sensor systems like night vision goggles, missile approach warning systems and telescopes have an increasing interest in decreasing their size and weight. At the same time optical aberrations are always more difficult to optimize with larger Focal Plane Arrays (FPAs) and larger field of view. Both challenges can now take advantage of a new optical parameter thanks to flexible microelectronics technologies: the FPA spherical curvature. This bio-inspired approach can correct optical aberrations and reduce the number of lenses in camera conception. Firstly, a new process to curve thin monolithic devices has been applied to uncooled microbolometers FPAs. A functional 256×320 25μm pitch (roughly 1cm2) uncooled FPA has been thinned and curved. Its electrical response showed no degradation after our process (variation of less than 2.3% on the response). Then a two lenses camera with a curved FPA is designed and characterized in comparison with a two lenses camera with a flat FPA. Their Modulation Transfer Functions (MTFs) show clearly an improvement in terms of beams dispersion. Secondly, a new process to fabricate monolithic cooled flip-chip MCT-IRCMOS FPAs was developed leading to the first spherical cooled IR FPA: with a radius of 550 mm. Other radii are achieved. A standard opto-electrical characterization at 80 K of the imager shows no additional short circuit and no mean response alteration compared to a standard IRCMOS shown in reference. Noise is also studied with a black body between 20 and 30°C.
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