Baffles design of the PROBA-V wide FOV TMA

Proba-V payload is a successor of the Vegetation instrument, a multispectral imager flown on Spot-4 and subsequently on Spot-5, French satellites for Earth Observation and defence. The instrument, with its wide field of view, is capable of covering a swath of 2200 km, which, in combination with a polar low Earth orbit, guarantees a daily revisit. The lifetime of Spot-5 expires in early 2013, and to ensure the continuity of vegetation data, BELSPO, the Belgian Federal Science Policy Office, supported the development of an instrument that could be flown on a Proba type satellite, a small satellite developed by the Belgian QinetiQ Space (previously known as Verhaert Space). The challenge of this development is to produce an instrument responding to the same user requirements as Vegetation, but with an overall mass of about 30 kg, while the Vegetation instrument mass is 130 kg. This development had become feasible thanks to a number of new technologies that have been developed since the nineties, when Vegetation was first conceived, namely Single Point Diamond Turning fabrication of aspherical mirrors and efficient VNIR and SWIR detectors. The Proba-V payload is based on three identical reflective telescopes using highly aspherical mirrors in a TMA (Three Mirrors Anastigmat) configuration. Each telescope covers a field of view of 34o to reach the required swath. One of the challenges in the development of the PROBA-V instrument is the efficient reduction of stray light. Due to the mass and volume constraints it was not possible to implement a design with an intermediate focus to reduce the stray light. The analysis and minimization of the in-field stray light is an important element of the design because of the large FOV and the surface roughness currently achievable with the Single Point Diamond Turning. This document presents the preliminary baffle layout designed for the Three Mirrors Anastigmatic (TMA) telescope developed for the Proba-V mission. This baffling is used to avoid 1st order stray light i.e. direct stray light or through reflections on the mirrors. The stray light from the SWIR folding mirror is also studied. After these preliminary analyses the mechanical structure of the TMA is designed then verified in term of vignetting and stray light

Development of linear variable filter and black coatings by PARMS technology for FLORIS HR focal plane array of FLEX mission

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Compact Optical Payload for Daily Survey of Vegetation from Small Satellites

Recent advancement of optics fabrication, metrology and detectors are the basis for the development of a new compact instrument designed to provide daily revisit for the analysis of vegetation. The instrument has been optimized to improve multispectral imaging capabilities with respect to Spot-Vegetation, while minimizing mass and power to be accommodated on a small satellite. The new technologies used for this instrument allow shrinking the mass and reducing the power consumption of a factor 5 with respect to Spot-Vegetation. The new instrument is designed to fly on Proba-V, a small satellite developed to ensure continuation of the Spot-Vegetation products.The paper gives an overview of the payload, presents its performance and explains which innovations allow a very compact design. In particular, the paper presents the technology used for the fabrication of mirrors, the approach used for their alignment, and the tests results obtained so far on the first prototype of the telescope. A section of the paper describes the InGaAs detector developed for the SWIR channel, a long linear array able to operate uncooled. The paper concludes with a description of the mission, of the payload accommodation on the small satellite, and of the data produced

Fluorescence Imaging Spectrometer (FLORIS) for ESA FLEX Mission

The Fluorescence Explorer (FLEX) mission has been selected as ESA’s 8th Earth Explorer mission. The primary objectives of the mission are to provide global estimates of vegetation fluorescence, actual photosynthetic activity, and vegetation stress. FLEX will fly in tandem formation with Sentinel-3 providing ancillary data for atmospheric characterization and correction, vegetation related spectral indices, and land surface temperature. The purpose of this manuscript is to present its scientific payload, FLORIS, which is a push-broom hyperspectral imager, flying on a medium size platform. FLORIS will measure the vegetation fluorescence in the spectral range between 500 nm and 780 nm at medium spatial resolution (300 m) and over a swath of 150 km. It accommodates an imaging spectrometer with a very high spectral resolution (0.3 nm), to measure the fluorescence spectrum within two oxygen absorption bands (O2A and O2B), and a second spectrometer with lower spectral resolution to derive additional atmospheric and vegetation parameters. A compact opto-mechanical solution is the current instrument baseline. A polarization scrambler is placed in front of a common dioptric telescope serving both spectrometers to minimize the polarization sensitivity. The telescope images the ground scene onto a double slit assembly. The radiation is spectrally dispersed onto the focal planes of the grating spectrometers. Special attention has been given to the mitigation of stray-light which is a key factor to reach good accuracy of the fluorescence measurement. The absolute radiometric calibration is achieved by observing a dedicated Sun illuminated Lambertian diffuser, while the spectral calibration in flight is performed by means of vicarious techniques. The thermal stabilization is achieved by using two passive radiators looking directly to the cold space, counterbalanced by heaters in a closed loop system. The focal planes are based on custom developed CCDs. The opto-mechanical design is robust, stable vs. temperature and easy to align. The optical quality is very good as recently demonstrated by the latest tests of an elegant breadboard. The scientific data products comprise the Top Of Atmosphere (TOA) radiance measurements as well as fluorescence estimates and higher-level products related to the health status of the vegetation addressing a wide range of applications from agriculture to forestry and climate

Stray-light analyses of the multielement telescope for imaging and spectroscopy coronagraph on Solar Orbiter

The modeling of the scattering phenomena for the multielement telescope for imaging and spectroscopy (METIS) coronagraph on board the European Space Agency Solar Orbiter is reported. METIS is an inverted occultation coronagraph including two optical paths: the broadband imaging of the full corona in linearly polarized visible-light (580 to 640 nm) and the narrow-band imaging of the full corona in the ultraviolet Lyman-\u3b1 (121.6 nm). METIS will have the unique opportunity of observing the solar outer atmosphere as close to the Sun as 0.28 AU and from up to 35 deg out-of-ecliptic. The stray-light simulations performed on the UV and VL channels of the METIS analyzing the contributors of surface microroughness, particulate contamination, cosmetic defects, and diffraction are reported. The results obtained with the nonsequential modality of Zemax OpticStudio are compared with two different approaches: the Monte Carlo ray trace with Advanced Systems Analysis Program (ASAP\uae) and a semianalytical model. The results obtained with the three independently developed approaches are in considerable agreement and show compliance to the requirement of stray-light level for both the UV and VL channels

Manuscrit composite: Mariano Taccola, De re militari et machinis bellicis. — Vue de Constantinople (?). — Carte des Balkans, vers 1453.

Contient : I. Ser Mariano di Giacomo Vanni, dit Taccola, De re militari et machinis bellicis ; II. Vue de ville (Constantinople ?). Carte de la péninsule balkanique ; III. Feuillets blancs ; IV. Textes divers en latin et en italienNumérisation effectuée à partir d'un document original : Latin 7239.Numérisation effectuée à partir d'un document de substitutionAu f. 1v, table ajoutée par une main du XVIIe s. qu’on trouve dans de nombreux manuscrits reliés pour la Bibliothèque royale à la fin du XVIIe s. Au f. de garde 163, copie à la plume de la tour du f. 106.Lieu de copie : VeniseLieu de copie : Venise

Manuscrit composite: Mariano Taccola, De re militari et machinis bellicis. — Vue de Constantinople (?). — Carte des Balkans, vers 1453.

Contient : I. Ser Mariano di Giacomo Vanni, dit Taccola, De re militari et machinis bellicis ; II. Vue de ville (Constantinople ?). Carte de la péninsule balkanique ; III. Feuillets blancs ; IV. Textes divers en latin et en italienNumérisation effectuée à partir d'un document original : Latin 7239.Numérisation effectuée à partir d'un document de substitutionAu f. 1v, table ajoutée par une main du XVIIe s. qu’on trouve dans de nombreux manuscrits reliés pour la Bibliothèque royale à la fin du XVIIe s. Au f. de garde 163, copie à la plume de la tour du f. 106.Lieu de copie : VeniseLieu de copie : Venise

Compact Hyperspectrals

Numerous Hyperspectral Imagers have been launched or are being built for resource management, monitoring anthropogenic effects on the troposphere gases, and for defense applications. Payloads such as Hyperion, EnMAP, HyspIRI, and SCHYAMACHY are instruments with mass in excess of 100 Kg. Technologies recently developed in precision manufacturing of aspherical mirrors, detectors, and spectral filters allow to shrink a hyperspectral instrument in an envelope that will fit on a small satellite, or even in a CubeSat. The reduction of mass, volume, and power is not the only problems to be solved to successfully use a hyperspectral on board of a small satellite. The amount of data acquired over one orbit can be as high as 1 TB (terabyte). To store and download the data can be unmanageable tasks for the resources of a small satellite. The reduced mass and volume of a compact hyperspectral comes at the expenses of a decreased signal to noise ratio. Can digital image processing and the knowledge acquired with the hyperspectral already in orbit help to compress the data to a manageable size? What type of information can be extracted from a compact hyperspectral? The paper describes the results obtained with the PhytoMapper, a technology demonstrator of a Compact Hyperspectral Instrument recently developed. The instrument fits in a volume of approximately 15 cm^3 (6 cubic inches) and has a mass of approximately 2 Kg. The instrument has a spectral resolution of 10nm, a field of view 34 degrees, and 2400 spectral bands. If flown on a 600km polar orbit, it will provide 100m spatial resolution and 3 days revisit time. The work presents the performance measured in the lab and the analyses performed to assess what type of mission objectives are achievable with this instrument. Further work has been done to push the envelope of a Hyperspectral within a CubeSat. A micro-telescope with a very aggressive optical design has been built and tested. The paper gives an overview of the performance that can be achieved with this extreme downscaled hyperspectral instrument and what, in the view of the Authors, can be the possible applications. A roadmap from the current technology status to the in-flight demonstration is finally presented