Satellite constellation with direct radio measurements for atmospheric studies: WATS mission case

Abstract

This paper shows the main results of a pre-feasibility study commissioned by the European Space Agency (ESA) in the framework of the Earth Explorer Core Mission programme. The analysed mission is called WATS (Water vapour and wind in Atmospheric Troposphere and Stratosphere) and aims to monitor variations and changes in the global atmospheric water vapour distribution and lower-stratosphere/upper-troposphere winds. Starting from a set of scientific requirements, the present work shows the main results of the mission analysis in terms of the number and spatial distribution of possible measurements. By performing trade-off with respect to expected values, the number of satellites forming the constellation has been fixed as well as the main orbital parameters, also taking into account degradations within the maximum expected mission lifetime. To assess the accuracy of the final measurement, a suitable performance model has been established that takes into account the effects of both the radio propagation of the signal through the atmosphere and the instrument receiving chain. The results obtained by running such a performance model are presented and discussed in order to assess the main system parameters mainly in terms of minimum transmitted power. Following, a sensitivity analysis is presented that shows the effects of antenna pointing error, receiver gain fluctuation, effective antenna size and pre-detection bandwidth.