MOLI instrument -for MOtionLess Interferometer- takes advantage of the new concept of static Fourier transform spectrometer. It is a high-resolution spectrometer working over a narrow bandwidth, which is adapted to a wide range of atmospheric sounding missions and compatible with micro-satellite platform.
The core of this instrument is an echelette cube. Mirrors on the classical design are replaced by stepped mirrors -integrated into that interference cube- thus suppressing any moving part. The steps’ directions being set over a perpendicular axis, the overlap of both stepped mirrors creates a cluster of so-called “echelettes”, each one corresponding to a different optical path difference (OPD). Hence the Fourier transform of the incoming radiance is directly imaged on a CCD array in a single acquisition.
The frequency domain of the measurements is selected by an interferential filter disposed on the incoming optical path. A rotating wheel equipped with several filters allows the successive measurement of spectra around some bands of interest, i.e. O2, CO2 and CO absorption bands.
A high-resolution super-spectral camera is being developed by Elbit Systems in Israel for the joint CNES- Israel Space Agency satellite, VENμS (Vegetation and Environment monitoring on a new Micro-Satellite). This camera will have 12 narrow spectral bands in the Visible/NIR region and will give images with 5.3 m resolution from an altitude of 720 km, with an orbit which allows a two-day revisit interval for a number of selected sites distributed over some two-thirds of the earth's surface. The swath width will be 27 km at this altitude. To ensure the high radiometric and geometric accuracy needed to fully exploit such multiple data sampling, careful attention is given in the design to maximize characteristics such as signal-to-noise ratio (SNR), spectral band accuracy, stray light rejection, inter- band pixel-to-pixel registration, etc. For the same reasons, accurate calibration of all the principle characteristics is essential, and this presents some major challenges. The methods planned to achieve the required level of calibration are presented following a brief description of the system design. A fuller description of the system design is given in [2], [3] and [4].
High resolution images in the Thermal infrared provide a way to detect irrigated fields, to measure evapo-transpiration
and detect plant water stress. Models and algorithms have largely improved to yield very good results. However the only
in-orbit satellites providing high resolution images in the thermal infrared domain (Landsat, Aster) are long beyond their
design lifetime. Furthermore, they do not provide frequent acquisitions (1 image every 16 days for Landsat and Aster,
while 1 image per couple of days would be required to monitor plant water stress). There is indeed a need for high
resolution and high repetitivity thermal infrared data for hydrological applications.
CNES carried out a feasibility study of such a mission on a microsatellite. The mission is called MISTIGRI
(MicroSatellite for Thermal InfraRed Ground Surface Imaging). The preliminary payload design was performed by
Thales Alenia Space for CNES. An instrumental concept was proposed which fulfils the mission requirements. The study
addressed both cooled and uncooled solutions, although a micro-bolometer detector was preferred after trade-off. This
paper addresses the results of the MISTIGRI payload feasibility study; it presents the mission requirements, the proposed
instrumental concept, describes the major subsystems and provides the preliminary performance budgets.
The Calipso mission aims to provide the geographic location, altitude and optical properties of cloud layers and aerosols
to help scientists understand how they shape climate processes. The payload is composed of three instruments, a two-wavelength
(532 nm and 1064 nm) polarization-sensitive backscatter Lidar, a Wide Field visible Camera (WFC) and the
Imaging Infrared Radiometer (IIR). The satellite was launched on the 28th of April 2006.
The IIR is an infrared three channel broadband radiometer which uses an uncooled infrared microbolometer detector.
The use of this microbolometer technology allows the design of compact and low-consumption infrared instruments
while providing acceptable radiometric performances.
The IIR provides calibrated infrared radiances at three wavelengths (B1 : 8.2-9.1 μm - B2 : 10.3-10.9μm - B3 : 11.55-
12.55 μm), which will be combined with daytime and nighttime lidar measurements to retrieve radiative and
microphysical parameters of clouds.
This paper reminds of the Calipso mission goal, then describes the IIR instrument architecture and highlights its main
features. It presents the performances achieved in flight by analysing the data provided by the IIR during checkout phase.
A 5m GSD satellite camera with 12 narrow spectral bands in the VNIR region is being developed by El-Op, Israel, for a cooperative project between CNES (France) and the Israel Space Agency. The satellite, called "VENμS" (Vegetation and Environment monitoring on a New Micro-Satellite) will enable evaluation of the use of high-resolution, high repetitivity, super-spectral imaging data for vegetation and environmental monitoring. The camera will image a limited number of selected sites around the globe with a two-day revisit interval. Highly demanding requirements for signal-to-noise ratio, radiometric accuracy, band-to-band registration and precise location on the ground will ensure the validity of the data. It will also help to define the optimal set of bands and the image processing algorithms of future instruments in the framework of the GMES program. The satellite bus will be built by Israel Aircraft Industries and will also carry an experimental ion propulsion system developed by Rafael (Israel).
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