LIMITS and POTENTIAL of FIXED WINGS and LTA

HAPS: fixed WINGS or LTA : limits and potentiality The presentation will discuss the limit and potentiality of the typology of two different HAPs. A fixed wings and a LTA platform. The two performances will be compared in the specific case of potential use of two proposed HAP in the framework of two different systems for on-going project and studies for deployment from space of innovative observation systems and concepts aimed at monitoring of the Earth's atmosphere. The first one is the Far-infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission, candidate mission for the Earth Explorer 9 programme, currently under competitive feasibility study. The second is the NDSA (Normalized Differential Spectral Attenuation) measurement of water vapour in the troposphere, an innovative technique for active sounding of atmospheric water vapour between two co-rotating (or counter-rotating) LEO satellites. Possible scenarios will be described in some detail of perspectives to deploy onboard the HAP an airborne version of the FORUM instrument and/or a demonstrator of the NDSA technique applied to water vapour measurements from a flying platform.