Entrée : HiRI
URI: https://terra-vocabulary.org/ncl/FAIR-Incubator/earthsciencesensors/c_a044a00a
HiRI of CNES with Thales Alenia Space (TAS-F) as the prime contractor for this instrument (formerly Alcatel Alenia Space). The objective is to provide high-resolution multispectral imagery with high geo-location accuracy. The camera design employs a pushbroom imaging concept. Extensive use of existing state-of-the-art technologies is made regarding such items as: a) camera alignment procedures, b) telescope thermal control and mechanical assembly principles, c) video processing techniques. 49) 50) 51) 52) 53) The industrial team consists of the following partners: • Thales Alenia Space, France: Instrument, telescope, detection unit, telescope structure & thermal control, video electronics, video power supply, harness • Thales Alenia Space España: Instrument service module • Sener: Shutter, detection unit structure & thermal control • E2V (Chelmsford, UK): Pan & MS CCD imaging detectors • SESO (Société Européenne de Systèmes Optiques), France: telescope mirror manufacturing • EADS Sodern: FPA (Focal Plane Assembly) • Sagem: Spectral filters. Equipment Technology Implementation Panchromatic detector CCD detector array with TDI (Time Delay Integration) mode of operation and anti-blooming structure High resolution imaging without satellite slowing. No light spreading due to blooming. Very long multispectral stripe filters Assembly of a single substrate with 4 stripe filters over the detector window Separate the different spectral bands in the FOV. Minimize chromatic aberrations Highly integrated detection unit Integrated focal plane and video electronics. Highly integrated ASIC technology Compact detection function integrated in the camera Telescope Carbon / carbon structure and light-weighted Zerodur optics Low mass/high thermal stability, highly polished mirror surfaces Optical assembly: The instrument employs a Korsch all-reflective 4 mirrors telescope design with TMA (Three Mirror Anastigmatic) optics. An additional plane mirror (MR) is used to enhance the instrument compactness. The imaging geometry optimization features a primary mirror size of 650 mm diameter, which suits well to the detectors performance and the orbit characteristics. The instrument architecture chosen is organized around a central plane structure supporting the primary mirror, the tertiary mirror, the plane mirror (MR), and a central cylinder that supports the secondary mirror. The optical assembly consists of an on-axis part (M1 + M2 collector mirrors) and an off-axis part (M3 + MR mirrors) feeding the different focal planes. The optics system of the instrument uses state-of-the-art techniques such as SiC-100 (silicon carbide) material for the mirrors and the telescope structure, specific detectors, and a modular video chain design. EADS Sodern is responsible for the development of the FPA. The FPA is offering a wide variety of new technologies for the imaging function. The size of the observed image is close to 400 mm and is analyzed in 30,000 samples in Pan and 7,500 in MS.. The focal plane assembly consists of two symmetrical arrangements of Pan and MS detectors. The beam splitter is made of a set of mirrors. The spectral selection is made by optical filters placed very close in front of the detectors. Pan filters and MS stripe line filters are space-qualified multi-layer coatings deposited on glass substrates. Each filter is composed of a high-pass filter and a low-pass filter. An absorbing material deposited between the MS filters isolates each band from the others to avoid interband straylight. Attitude sensors (star tracker heads and gyroscope heads) are placed on this central instrument structure to improve the performance. A dedicated supporting truss structure ensures the instrument interface with respect to the bus. The detector thermal radiator has its own supporting structure. The instrument design employs carbon material for the structure (the carbide characteristics are: very low coefficient of thermal expansion, very low density, resulting in a light telescope, and a simple thermal control) and Zerodur material for the mirrors. The instrument focus mechanism is placed onto the tertiary mirror. This position offers an optimum between mechanism and accuracy. The instrument includes also an internal shutter to protect it from sun radiation in non-operational phases such as launch, attitude acquisition, or safe modes. The shutter is placed behind the primary mirror to protect only the tertiary mirror and the detection cavity. Spectral bands Pan: 480-820 nm; TDI is only used for Pan data MS bands in nm B0= 450-530 (blue), B1= 510-590 (green), B2= 620-700 (red), B3= 775-915 (NIR) Optical system 65 cm aperture diameter, focal length of 12.905 m, f/20, TMA optics Spatial resolution, GSD 0.7 m for Pan, 2.8 m for MS bands Swath width, FOR 20 km at nadir, 60º (FOR=Field of Regard); Each satellite will be able to collect imagery anywhere within an 800 km wide ground strip, covering 200 km in 11 s or 800 km in 25 s, including stabilization time. SNR > 147 (Pan), > 130 (MS) MTF in Pan band 0.07 at Nyquist frequency fe/2 (1/2 x 0.7 m-1) Note: “fe” is the sampling frequency (fréquence d'échantillonnage) Detectors Pan array assembly: 5 x 6000 (30,000 pixels cross-track) pixel size: 13 µm MS array assembly: 5 x 1500 (7500 pixels in cross-track) pixel size: 52 µm TDI detector data rate 290 Mpixel/s (total) or about 700 Mbit/s per detector; or 3.5 Mbit/s (max) Data quantization 12 bit per pixel (correlated dual sampling) Image location accuracy 1 m (with ground control points), 20 m without GCP (99.7%), 10 m (90%) Image location accuracy <0.9 pixel Pan over 12 s with a time linear error model (with GCPs) Line-of-sight frequency <0.1 pixel (dynamic stability) Source data rate, downlink 4.5 Gbit/s (max), 465 Mbit/s in 3 x 155 Mbit/s X-band channels Data compression Wavelet compression algorithm with an average compression factor of 4 Instrument mass, power ~ 195 kg (< 14 service electronics), ~ 400 W Instrument size L < 1594 mm W < 980 mm H < 2235 mm Pointing agility of S/C Roll of 60º within 25 s; Pitch of 60º within 25 s.