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Human activities have been identified as critical contributors to climate changes. Modern industrial development and increasing urbanisation have been affecting the environment at an unprecedented scale since the 19th century. In the two last decades the process has become even faster, also due to the impressive development of largely populated countries like India and China. Historical data records testify a direct correlation between increase in atmospheric CO2 levels and Earth's temperatures but processes underlying climate regulation and changes are only partially known. The improvement of knowledge of atmosphere and climate processes needs the availability of complete and reliable data about atmospheric composition and properties and space-based observations play a primary role. Implementation of a demonstration mission based on an occultation technique at optical wavelengths is proposed. Observations in the infrared spectral range vest a particular importance because this band exhibits many absorptive spectral lines due to greenhouse gases, identified as the main responsible of global warming, thus H2O, CO2, CH4, N2O, O3, and others can be observed with high accuracy. It is expected that the mission will demonstrate technical feasibility of an optical payload for limb sounding observations and provide useful inputs to climatic benchmarking (greenhouse gases and wind profile, as well as atmospheric thermodynamic properties). The identification and the preliminary definition of the instrument architecture and the identification of the critical technologies have been among the main tasks. Possible design options for the laser transmitter and the receiver are discussed, considering available technological solutions and technical constraints. Potential technological criticalities are illustrated too. The creation of performance models, analytical and numerical, facilitates and addresses the payload design activity, both at instrument level and at general system level.
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