KEYWORDS: Staring arrays, Modulation transfer functions, Signal to noise ratio, Multispectral imaging, Sensors, Polonium, Astronomical imaging, Satellites, Defense and security, Short wave infrared radiation
The development and testing of the MSI PFM for the first Sentinel-2 satellite is now completely achieved, in particular tests and characterization of the VNIR FPA and of the whole instrument. This paper provides main results obtained for the 12 VNIR detection chains of the Sentinel-2 Multi-Spectral Instrument and highlights some of the most outstanding characteristics and performances achieved.
The Sentinel-2 multi-spectral instrument (MSI) will provide Earth imagery in the frame of the Global Monitoring for
Environment and Security (GMES) initiative which is a joint undertaking of the European Commission and the Agency.
MSI instrument, under Astrium SAS responsibility, is a push-broom spectro imager in 13 spectral channels in VNIR and
SWIR. The instrument radiometric calibration is based on in-flight calibration with sunlight through a quasi Lambertian
diffuser. The diffuser covers the full pupil and the full field of view of the instrument. The on-ground calibration of the
diffuser BRDF is mandatory to fulfil the in-flight performances.
The diffuser is a 779 x 278 mm2 rectangular flat area in Zenith-A material. It is mounted on a motorised door in front of
the instrument optical system entrance. The diffuser manufacturing and calibration is under the Centre Spatial of Liege
(CSL) responsibility.
The CSL has designed and built a completely remote controlled BRDF test bench able to handle large diffusers in their
mount. As the diffuser is calibrated directly in its mount with respect to a reference cube, the error budget is significantly
improved. The BRDF calibration is performed directly in MSI instrument spectral bands by using dedicated band-pass
filters (VNIR and SWIR up to 2200 nm). Absolute accuracy is better than 0.5% in VNIR spectral bands and 1% in SWIR
spectral bands. Performances were cross checked with other laboratories.
The first MSI diffuser for flight model was calibrated mid 2013 on CSL BRDF measurement bench. The calibration of
the diffuser consists mainly in thermal vacuum cycles, BRDF uniformity characterisation and BRDF angular
characterisation. The total amount of measurement for the first flight model diffuser corresponds to more than 17500
BRDF acquisitions.
Performance results are discussed in comparison with requirements.
The MSI PFM campaign is built around 4 major steps : the focal planes alignment and testing, the telescope alignment
and testing, the instrument performance testing and the instrument environmental qualification.. This paper presents the
results of the first 3 steps covering major performance aspects of the Sentinel-2 Multi-Spectral Instrument.
W. Gielesen, D. de Bruijn, T. van den Dool, F. Kamphues, J. Mekking, B. Calvel, A. Laborie, C. Coatantiec, S. Touzeau, M. Erdmann, P. Gare, D. Monteiro
The Gaia mission1 will create an extraordinarily precise three-dimensional map of more than one billion stars in our
Galaxy. The Gaia spacecraft2, built by EADS Astrium, is part of ESA's Cosmic Vision programme and scheduled for
launch in 2013. Gaia measures the position, distance and motion of stars with an accuracy of 24 micro-arcsec using two
telescopes at a fixed mutual angle of 106.5°, named the ‘Basic Angle’, at an operational temperature of 100 K. This
accuracy requires ultra-high stability at cryogenic conditions, which can only be achieved by using Silicon Carbide for
both the optical bench and the telescopes. TNO has developed, built and space qualified the Silicon carbide Basic Angle
Monitoring (BAM) on-board metrology system3 for this mission, measuring the relative motion of Gaia’s telescopes with
accuracies in the range of 0.5 micro-arcsec. This is achieved by a system of two laser interferometers able to detect
Optical Path Differences (OPD) as small as 1.5 picometer rms. Following a general introduction on Gaia and the use of
Silicon Carbide as base material this paper addresses the specific challenges towards the cryogenic application of the
Gaia BAM including design, integration and verification/qualification by testing.
The Gaia mission will create an extraordinarily precise three-dimensional map of more than one billion stars in our
Galaxy. The Gaia spacecraft, built by EADS Astrium, is part of ESA's Cosmic Vision programme and scheduled for
launch in 2013. Gaia measures the position, distance and motion of stars with an accuracy of 24 micro-arcsec using two
telescopes at a fixed mutual angle of 106.5°, named the ‘Basic Angle’. This accuracy requires ultra-high stability, which
can only be achieved by using Silicon Carbide for both the optical bench and the telescopes. TNO has developed, built
and space qualified the Silicon carbide Basic Angle Monitoring (BAM) on-board metrology system for this mission.
The BAM measures the relative motion of Gaia’s telescopes with accuracies in the range of 0.5 micro-arcsec. This is
achieved by a system of two laser interferometers able to measure Optical Path Differences (OPD) as small as 1.5
picometer rms. Following a general introduction to the Gaia mission, the Payload Module (PLM) and the use of Silicon
Carbide as base material, this presentation will address an overview of the challenges towards the key requirements,
design, integration and testing (including space-level qualification) of the Gaia BAM.
The astronomic mission Gaia is a cornerstone mission of the European Space Agency, due for launch in the 2011 time
frame. Requiring extremely demanding performance, Gaia calls for the development of an unprecedented large focal
plane featuring innovative technologies. For securing the very challenging Gaia Focal Plane Assembly (FPA)
development, technology activities have been led by EADS Astrium from 2002 to 2005. After EADS Astrium selection
for the development of the Gaia satellite, the program started in early 2006.
The all-Silicon Carbide FPA hosts all the mission scientific functions for Astronometry, Photometry and Radial Velocity
Spectrometry, encompassing 106 large scientific CCDs operated in TDI mode with windowing readout. With a sensitive
area of about half a square meter, the FPA includes more than 935 millions of 10 μm x 30 μm pixels. To fulfill all the
requirements, the CCDs feature a specific design with a Silicon Carbide package and on-chip functions such as TDI
dynamic gain control and pulsed charge injection. Main development issues are related to the mass production of CCDs,
and extremely low noise and miniaturized focal plane electronics. Finally, the major challenge of the overall focal plane
mechanical and thermal accommodation is to allow full modularity while providing perfectly stable temperature and
efficient thermal decoupling between the CCDs area (160 K - 170 K) and electronics operated in standard temperature
conditions.
KEYWORDS: Charge-coupled devices, Electrons, Monte Carlo methods, Point spread functions, Calibration, Radiation effects, Data modeling, Telescopes, Modulation transfer functions, Motion models
ESA's Gaia astrometry mission is due for launch in 2011. The astrometric instrument focal plane will have an area of up to 0.5m2 and will contain more than 100 CCDs. These will be operated in Time Delay and Integration mode in order to track and observe sources whilst the telescopes continuously scan the sky. Gaia's target for astrometric precision of a few millionths of an arc second, places extreme demands on focal plane thermo--mechanical stability and electronics performance. The CCDs themselves are large area, back illuminated, full--frame, four phase devices. They require maximum efficiency for observing the majority of (faint) objects, yet must simultaneously be able to handle very bright objects that will regularly cross the field of view. Achieving the final astrometric precision will also require excellent noise performance and MTF. In addition to demanding excellent performance from each CCD, they will need to be produced in large numbers which raises production and yield issues. When analyzing Gaia data it will be essential to understand and calibrate CCD behaviour correctly, including the expected performance degradation due to radiation damage. This is being addressed through comprehensive testing and the development of CCD models.
The ESA cornerstone mission GAIA will perform astrometric and photometric measurements on one billion objects, and is due for launch in 2010 into L2 orbit. The key astrometric focal plane will comprise over 180 large area CCDs with a focal surface of about 0.5m2. The 45x60mm2 CCDs for the focal plane will include technical features new to CCDs. This paper will discuss the characteristics of these devices, including the measures to improve the radiation hardness of the technology.
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