Natural and anthropogenic trace constituents play an important role for the ozone budget and climate as well as in other problems of the environment. In order to prevent the dramatic impact of any climate change, exchange processes between the stratosphere and troposphere as well as the distribution and deposition of tropospheric trace constituents are investigated.
The Limb Infrared Fourier Transform spectrometer (LIFT) will globally provide calibrated spectra of the atmosphere as a function of the tangent altitude.
LIFT field of view will be 30 km × 30 km. The resolution is 30 km in azimuth corresponding to the full field of view, and 2 km in elevation, obtained by using a matrix of 15×15 detectors. The instrument will cover the spectral domain 5.7-14.7 μm through 2 different bands respectively 13.0-9.5 μm, 9.5-5.7 μm.
With a spectral resolution of 0.1 cm-1, LIFT is a high class Fourier Transform Spectrometer compliant with the challenging constraints of limb viewing and spaceborne implementation.
The WAter vapour Lidar Experiment in Space (WALES) mission aims at providing water vapour profiles with high accuracy and vertical resolution through the troposphere and the lower stratosphere on a global scale using an instrument based on Differential Absorption Lidar (DIAL) observation technique, and mounted on an Earth orbiting satellite.
This active DIAL technique will also provide data on the cloud coverage by means of the signal reflection on the cloud layers.
In DIAL operation, backscatter lidar signals at two wavelengths - at least - are detected. One wavelength (λ ON) is highly absorbed by the species of interest, while the other (λ OFF) is backscattered with minimal absorption. This difference in absorption at the two transmitted wavelengths leads to the determination of the concentration of the species of interest.
The DIAL is therefore a dual-wavelength lidar in which the signals detected at the two wavelengths are processed to extract the absolute density of water vapour.
The Phase A study performed by ALCATEL Space and their partners under contract of the European Space Agency has led to a credible and innovative concept of instrument, based on a mission performance modelling. The challenge is to foster the scientific return while minimising the development risks and costs of instrument development, in particular the laser transmitter.
The paper describes the payload design and the implementation on a low Earth orbiting (LEO) satellite.
This paper describes a concept of a formation flyer for ASPICS (Association de Satellites Pour l'Imagerie et la Coronagraphie Solaire), a giant 100 m based, externally occulted coronagraph aimed at observing the inner corona (and the solar disk) in the visible and ultra-violet. The two-satellite formation approach, based on existing space systems, is composed of a Myriade micro-satellite supporting the occulter and a Proteus platform as the main system carrying the coronagraph and imager scientific instruments. Both spacecrafts are launched as a single composite and deployed once on orbit, preferably a 3-day orbit or at the L1 Lagrange point. The coronagraph satellite acts as the "master" and provides the main functions of the mission (data handling, communication, propulsion, Guidance Navigation and control) while the Myriade acts as the "slave". The control of the formation is performed in two steps: i) RF metrology for deployment and preliminary pointing, ii) classical optical attitude sensors and metrology based on diverging laser beams. This will insure the nominal requirement of a lateral positioning with an accuracy of 1 mm and a longitudinal positioning with an accuracy of 500 mm.
Natural and anthropogenic trace constituents play an important role for the ozone budget and climate as well as in other problems of the environment. Atmospheric trace aerosol distribution plays an important role in key evolutions of the Earth atmosphere, such as stratospheric ozone depletion and greenhouse effects. In order to monitor those changes and to try to prevent their dramatic impact, exchange processes between the stratosphere and troposphere as well as the distribution and deposition of tropospheric trace constituents are investigated. The mission and the design of the Limb Infrared Fourier Transform spectrometer (LIFT) instrument are described. This instrument supply observation of species with regard to eight specific questions centred on climate-chemistry interactions and the role of anthropogenic emissions. LIFT will globally provide calibrated spectra of the atmosphere as a function of the tangent altitude. The users will subsequently retrieve altitude profiles of the target species from the spectra. LIFT field of view will be 30 km in elevation and in azimuth. The resolution of this instrument is 30 km in azimuth corresponding to the full field of view, while it is only 2 km in elevation, obtained by using a matrix of 15x15 detectors. The instrument will cover the spectral domain 5.7-14.7 μm through 2 different bands respectively 13.0-9.5 μm, 9.5-5.7 μm. With a spectral resolution of 0.1 cm-1, LIFT is a high class Fourier Transform Spectrometer compliant with the challenging constraints of limb viewing and spaceborne implementation.
Research on optical communication behavior in radiative environments is a key point for the design of diagnostic links for the large physic instruments (Laser MegaJoule at CEA, Large Hadron Collider at CERN). For years, the radiation tolerance of several types of emitters (light emitting diode and laser diode (LD)) have been tested with promising results for the LDs. New technologies and devices (Vertical-Cavity Surface-Emitting Lasers (VCSEL)) have recently appeared as promising candidates to replace conventional edge emitting LDs. The shorter wavelength VCSELs (below 1 micrometers ) are well adapted for short distance data links, due to their low threshold current, high efficiency and large possibilities for integration.
The effect of radiation damage on carrier lifetime in 1310 nm InGaAsP/InP multi-quantum-well lasers irradiated with 0.8 MeV neutrons, was investigated for fluences up to 6.9 X 1014 n/cm2. The damage to the carrier lifetime was studied by measuring the transient response of irradiated lasers to incident optical pulses of 1064 nm and 532 nm wavelength, and by relative intensity noise measurements. The carrier lifetime was determined to be degraded to a similar extent in both the InGaAsP laser cavity and the surrounding InP material following radiation damage.
A transmission data link has been simulated using a high speed digital signal to modulate a 1300 nm laser diode. A Nd:YAG laser was used to simulate ionizing effects induced by transient particle irradiation on the laser diode by creating carriers only in the laser cavity. With this method, calibration of ionizing effects, error amplitude and influence of operational parameters of the link (frequency, amplitude of modulation...) have been studied. Heavy ions at different energies have been used to confirm transient effects, but the perturbation duration, too short compared with the Nd:YAG, have limited observation of the transient error due to ionizing effects. Permanent damages have been observed and their origin linked with the particle.
Electro-optic data links are of increasing importance due to their high bandwidth, low losses and intrinsic immunity to electromagnetic interference. Nevertheless as most data processors are using electrical signals electro-optic devices like laser diodes are required to convert electrons to photons. In radiative environments encountered in satellite applications or large physics experiments, this conversion can be perturbed which results in information lost. Most previous works investigate the behavior of electro-optic devices under total dose effects, in connection with the determination of device lifetime. Transient irradiation effects, that could affect data transmissions, are rarely considered. To induce transient effects in laser diodes, we used a 30 picosecond tunable laser. Tuning wavelength near the III-V semiconductor energy bandgap allows us to generate selectively electron-hole pairs in the various materials and regions of the device. By pumping carriers with this method, we have been able to observe differences between bulk and multi-quantum-wells laser cavities. When the whole device is irradiated, we also observe a strong dependence on device structure and technology. These data are useful for the manufacturers, because they evidence the intrinsic limitations of a laser diode technology that can not be investigated by standard electrical and optical characterizations.