Nanosats or CubeSats are emerging technologies corresponding to miniaturized satellites with a wet mass between 1 and 10kg. In this study, we explored the possibility of doing earth observation in the longwave infrared. The challenge is to integrate the longest focal length as possible in a 2U volume dedicated to the optical payload. Another challenge is to use a low cost, lightweight and low power consumption microbolometer which requires high apertures optics. For these volumes, there is a competition between refractive designs, often more compact when having high apertures, and reflective designs, having a lower mass and being easily athermalized. The choice is not obvious and we studied a telephoto refractive design and an off-axis Three Mirror Anastigmat (TMA) reflective design. The key technology for the telephoto design is the use of chalcogenide glasses whereas the key technology for the TMA is the use of freeform surfaces.
The goal of a cophasing sensor (CS) is to measure the phase disturbances between the sub-apertures or inside each aperture of a telescope. Three CSs are currently studied at ONERA. A first CS for Earth imaging is based on phase diversity on extended sources (cf companion paper by L. Mugnier). A second CS for intercalibration uses phase retrieval on a point source. The third CS for nulling interferometry (“DWARF”, for the ESA/DARWIN mission) is based on similar algorithms. To test performance of these CSs, ONERA has defined and integrated a multipurpose bench, “BRISE”. Its main features are the simultaneous imaging of a point source and of an extended source, the minimisation of absolute and differential disturbances, the use of any aperture configuration and the generation of pure calibrated piston/tip/tilt aberrations on three sub-apertures by a dedicated PZT-based device. Preliminary experimental results are consistent with numerical simulations and confirm nanometric performance.
SYSIPHE is an airborne hyperspectral imaging system, result of a cooperation between France (Onera and DGA) and
Norway (NEO and FFI). It is a unique system by its spatial sampling -0.5m with a 500m swath at a ground height of
2000m- combined with its wide spectral coverage -from 0.4μm to 11.5μm in the atmospheric transmission bands.
Its infrared component, named SIELETERS, consists in two high étendue imaging static Fourier transform
spectrometers, one for the midwave infrared and one for the longwave infrared. These two imaging spectrometers are
closely similar in design, since both are made of a Michelson interferometer, a refractive imaging system, and a large
IRFPA (1016x440 pixels). Moreover, both are cryogenically cooled and mounted on their own stabilization platform
which allows the line of sight to be controlled and recorded. These data are useful to reconstruct and to georeference the
spectral image from the raw interferometric images.
The visible and shortwave infrared component, named Hyspex ODIN-1024, consists of two spectrographs for VNIR and
SWIR based on transmissive gratings. These share a common fore-optics and a common slit, to ensure perfect
registration between the VNIR and the SWIR images. The spectral resolution varies from 5nm in the visible to 6nm in
the shortwave infrared.
In addition, the STAD, the post processing and archiving system, is developed to provide spectral reflectance and
temperature products (SRT products) from calibrated georeferenced and inter-band registered spectral images at the
sensor level acquired and pre-processed by SIELETERS and Hyspex ODIN-1024 systems.
Sysiphe is an airborne hyperspectral imaging system, result of a cooperation between France (Onera and DGA) and
Norway (NEO and FFI). It is a unique system by its spatial sampling -0.5m with a 500m swath at a ground height of
2000m- combined with its wide spectral coverage -from 0.4μm to 11.5μm in the atmospheric transmission bands. Its
infrared component, named Sieleters, consists in two high étendue imaging static Fourier transform spectrometers, one
for the midwave infrared and one for the longwave infrared. These two imaging spectrometers have very close design,
since both are made of a Michelson interferometer, a refractive imaging system, and a large IRFPA (1016x440 pixels).
Moreover, both are cryogenic and mounted on their own stabilization platform which allows at once to actively control
and independently measure the line of sigh. These data are useful to reconstruct and to georeference the spectral image
from the raw interferometric images. Sysiphe first flight occurred in September, 2013.
The SYSIPHE system is the state of the art airborne hyperspectral imaging system developed in European cooperation.
With a unique wide spectral range and a fine spatial resolution, its aim is to validate and quantify the information
potential of hyperspectral imaging in military, security and environment applications. The first section of the paper recalls the objectives of the project. The second one describes the sensors, their implementation onboard the platform and the data processing chain. The last section gives illustrations on the work in progress.
This paper presents the new-generation airborne remote sensing systems SETHI and SYSIPHE, developed by ONERA,
the French Aerospace Lab, and dedicated to environmental, scientific and security applications.
Today, many scientists from climatologists to agronomists, need specific types of information that cannot be provided in
full by conventional observation systems to solve complex problems. Onera offers them a solution to use the huge
potential of multispectral and hybrid radar/optronics data.
The SETHI remote sensing system is dedicated to provide a unique combination of radar and optronics images, including
polarimetric SAR, visible and short wave infrared, multispectral images, ... This all-in-one system is operational from
2008 in radar configuration, its optronics capability becomes operational gradually.
The SYSIPHE system is the state of the art airborne hyperspectral imaging system developed in European cooperation.
With a unique wide spectral range and a fine spatial resolution, its aim is to validate and quantify the information
potential of hyperspectral imaging in military, security and environment applications.
The first section of the paper introduces the objectives of the projects and their general architecture. The second one
describes the sensors, their implementation onboard the platforms, the data processing chain and gives an overview of
the projects planning. The third section presents some significant results.
KEYWORDS: Cameras, Control systems, Line of sight stabilization, Optical imaging, Target acquisition, Imaging systems, Target designation, Detection and tracking algorithms, Filtering (signal processing), Digital signal processing
In an airborne optical imaging system, a key function is to command and control the observation direction or line of sight whose aim is to track various targets during a determined period. Indeed, the optical images will be affected by the residue of pointing.
Moreover, the airborne environment adds complementary difficulties on the line of sight control. The Line of sight command is composed of three phases : the "designation", the "hanging" and the "tracking" phases. Each of one is characterized by a specific control law. The first one allows to place the instrument line of sight following the provisional target trajectory. The second control law is optimized for the target acquisition and the third one is dedicated to track the target. The acquired imagery allows, after validation of the known target and/or rallying it by human intervention, to calculate an angular deflection for measurement of tracking error. According to the scientific objective of the imaging system, various types of targets could be observed. So the angular deflection measurement is calculated by barycentric or images correlation methods. This information is injected into the second control law which will be substituted, without unhooking, to the first performed for designation. The line of sight of the imaging system is realized with a gyro-mirror for the fine pointing in front of a camera and an independent mechanical framework, supporting the camera and the gyro-mirror. This pedestal offers to the instrument a wide angular field of view but a coarse pointing. These elements individually controllable are dimensioned for the design and realization for the control law. This paper presents each station to study needs for the definition and the realization of the control law for an airborne optical imaging instrument. This paper also describes an approach of the harmonization of the lines of sight of different instruments pointing the same target.
Onera has designed and developed an scientific airborne infrared measurement system. This system is constituted of a supervisor computer and two scientific instruments (a cryogenic IR multiband camera and a cryogenic IR spectro-radiometer). This article presents the different elements of the system and focuses on the design of the cryogenic IR camera. The IR camera design involves instrument control, data acquisition, IRIG time stamping, target acquisition and tracking. This article highlights also the communication design using two Ethernet networks linking the elements of the experimental measurement chain.
A Shack-Hartmann wave-front sensor has been used to characterize non-isotropic turbulence simulated in a transonic wind-tunnel. Wavefront measurements have been obtained for a large number of turbulent conditions.
The phase 2-D power spectra exhibit standard Kolmogorov -11/3 power law but also -17/3 power law in the transverse direction, which appears to be a new characteristic for such turbulent flows. Results are further discussed in terms of the various simulated turbulent parameters.
We have designed, realized and tested a dedicated software tool defined so as to enable a wide non-specialist community to perform optimal adaptive optics observations with VLT instrument NAOS-CONICA. We first precise the requirements derived from NAOS complexity due to a large number of configurations, ESO/VLT operational policy including service mode observations and limited human interaction during observations, and astronomical observation requirements. We then present the developed software tool, so-called "Preparation Software", that couples a user-friendly interface that accepts observation conditions (including seeing, star magnitude etc...) and an elaborate simulator of adaptive optics based on the NAOS characteristics.
Adaptive Optics as a new tool for astronomical observation has proved a powerful means of investigation in high angular resolution programs. However, in spite of the complexity of the components involved (wavefront sensor, real-time computer), its use must be made as simple as possible in order to make it accessible to the largest audience of observers, and to answer the more demanding needs of modern observatories such as queue scheduling, service observing or remote observing. The Computer Aided Control developed for the Nasmyth Adaptive Optics System of the Very Large Telescope, will provide the astronomer with an extensive support, from the preparation of optimized observations to the automated operation of the instrument at the telescope either for hardware control, real time computing, or even preventive maintenance.
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