A novel satellite mission concept for upper air water vapour, aerosol and cloud observations using Integrated Path Differential Absorption LiDAR Limb Sounding

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• Alex Hoffman, University of Cambridge
• Monday 28 November 2011, 14:15-15:15
• Unilever Lecture Theatre, Department of Chemistry.

If you have a question about this talk, please contact Dr Alex Archibald.

In this talk, I am going to present a collaborative new Earth Observation space-mission concept conceived during the Alpbach Summer School 2010 and further developed during the Obergurgl 2010 follow-up workshop. Our team proposed a new satellite constellation to deliver high quality measurements of upper air water vapour. The concept centres around a LiDAR in limb sounding by occultation geometry, designed to operate as a monostatic very long path system for differential absorption measurements. A secondary payload of a fairly conventional medium resolution multispectral radiometer allows wide-swath cloud and aerosol imaging. I will make a case for the scientific objectives of the proposed mission, but predominantly focus on some of its high-level engineering aspects.

In this regard, I will present some of the numerous challenges encountered in and characteristic for such an integrated design project, along with some of the successive trade-offs and intermediate design solutions proposed. Some of these challenges include orbit and constellation considerations, performance of laser systems in space, retroreflector and telescope concerns as well as pointing, acquisition and tracking issues and spacecraft attitude control.

I will conclude on a preliminary performance analysis with a system sized to send 75mJ pulses at 25Hz at four wavelengths close to 950nm, to up to 5 microsatellites in a counter-rotating orbit, carrying retroreflectors characterized by a reflected beam divergence of roughly twice the emitted laser beam divergence of 15 microrad. This provides water vapour profiles with a vertical sampling of 110m; preliminary calculations suggest that the system could detect concentrations of less than 5ppm up to roughly 40-50 km of altitude.

This talk is part of the Centre for Atmospheric Science seminars, Chemistry Dept. series.

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