Remote Sens._**2012**, \(4\), 867-910; doi:10.3390/rs4040867  
_Remote Sensing_  
**ISSN 2072-4292**  
www.mdpi.com/journal/remotesensing  
_Article_  
**A Novel Satellite Mission Concept for Upper Air Water Vapour, Aerosol and Cloud Observations Using Integrated Path Differential Absorption LiDAR Limb Sounding**  
**[PERSON] \({}^{1,\star}\), [PERSON] \({}^{2}\), [PERSON] \({}^{3}\), [PERSON] \({}^{4}\), [PERSON] \({}^{5}\), [PERSON] \({}^{6}\), [PERSON] \({}^{7}\), [PERSON] \({}^{8}\), [PERSON] \({}^{9}\), [PERSON] \({}^{10}\), [PERSON] \({}^{11}\), [PERSON] \({}^{12}\), [PERSON] \({}^{13}\), [PERSON] \({}^{14}\) and [PERSON] \({}^{15}\)**  
\({}^{1}\) Centre for Atmospheric Science, Department of Geography, University of Cambridge, Downing Place, Cambridge CB2 3 EN, UK  
\({}^{2}\) National Centre for Earth Observation, University of Reading, Earley Gate, Whiteknights, Reading RG6 6 BB, UK; E-Mail: [EMAIL_ADDRESS]  
\({}^{3}\) Computer Vision and Robotics group, University of Girona, Campus de Montilivi, P4 building, E-17071 Girona, Spain; E-Mail: [EMAIL_ADDRESS]  
\({}^{4}\) School of Mechanical and Manufacturing Engineering, Dublin City University, Collins Avenue, Dublin 9, Ireland; E-Mail: [EMAIL_ADDRESS]  
\({}^{5}\) Institut Superieur de l'Aeronautique et de l'Espace, Supaero, 4 Avenue [PERSON], F-31054 Toulouse, France; E-Mail: [EMAIL_ADDRESS]  
\({}^{6}\) Department of Geology, University of Toronto, Toronto, ON M5S 3B1, Canada; E-Mail: [EMAIL_ADDRESS]  
\({}^{7}\) Systems and Concurrent Engineering Section, ESTEC, ESA, Keplerlaan 1, 2200 AG Noordwijk, The Netherlands; E-Mail: [EMAIL_ADDRESS]  
\({}^{8}\) Department of Geography and Regional Science, University of Graz, Heinrichstrasse 36, A-8010 Graz, Austria; E-Mail: [EMAIL_ADDRESS]  
\({}^{9}\) Institute of Atmospheric Physics, German Aerospace Center, Oberpfaffenhofen, D-82234 Wessling, Germany; E-Mail: [EMAIL_ADDRESS]  
\({}^{10}\) Institute for Energy Systems and Thermodynamics, Vienna University of Technology, Getreidemarkt 9/6, A-1060 Vienna, Austria; E-Mail: [EMAIL_ADDRESS]  
\({}^{11}\) Institute of Environmental Physics (IUP), University of Bremen FB1, Otto Hahn Allee 1, D-28334 Bremen, Germany; E-Mail: [EMAIL_ADDRESS]  
\({}^{12}\) Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford OX1 3 PU, UK; E-Mail: [EMAIL_ADDRESS]  
\({}^{13}\) Institute of Communication Networks and Satellite Communications, Graz University of Technology, Infeldgasse 12, A-8010 Graz, Austria; E-Mail: patrick.romano@gmail.comInternational Space University, F-67400 Illkirch-Graffenstaden, France;  
E-Mail: [EMAIL_ADDRESS]  
Institute for Geography, University of Augsburg, Universitaetsstrasse 1 a, D-86159 Augsburg,  
Germany; E-Mail: [EMAIL_ADDRESS]  
Author to whom correspondence should be addressed; E-Mail: [EMAIL_ADDRESS];  
Tel. : +44-1223-766-581, Fax: +44-1223-333-392. Received: 21 February 2012; in revised form: 15 March 2012 / Accepted: 20 March 2012 /  
_Published: 27 March 2012_  
**Abstract:** We propose a new satellite mission 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 very long path system for differential absorption measurements. We present a preliminary performance analysis with a system sized to send 75 mJ pulses at 25 Hz at four wavelengths close to 935 nm, 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 \(\mu\)rad. This provides water vapour profiles with a vertical sampling of 110 m; preliminary calculations suggest that the system could detect concentrations of less than 5 ppm. A secondary payload of a fairly conventional medium resolution multispectral radiometer allows wide-swath cloud and aerosol imaging. The total weight and power of the system are estimated at 3 tons and 2,700 W respectively.