A space-borne Doppler radar end-to-end simulator for the ESA WIVERN mission

In June 2021, the WIVERN (WInd VElocity Radar Nephoscope) mission has been selected to enter Phase 0 studies in the context of the 11th call of the ESA Earth Explorer program. The mission will provide novel observations of global winds, clouds and precipitation by a ground-breaking conically scanning dual-polarization Doppler W-band (94-GHz) radar. End-to-End (E2E) simulators represent critical tools to assess in-flight performances and support the consolidation of mission architecture and payload design and are essential during Phase 0 ESA studies and beyond. This dissertation describes the original work carried out to develop an E2E radar simulator tailored to the WIVERN mission, showcasing its capabilities for a case study of interest. The simulator reproduces WIVERN observations by simulating the satellite orbiting around the Earth in a polar Sun-synchronous orbit and looking down at an atmosphere described by a global circulation model that provides fine resolution vertical profiles of winds and clouds. The simulator implements the orbital model, the scanning geometry and the different polarization modes of the radar, thus identifying the volume sampled by the radar over time. The radar sampled volume is then linked to the output of the global cloud model to derive the Level 2a products of the mission, i.e. measured reflectivities and Doppler velocities of the atmospheric targets. The simulator also addresses specific issues affecting the radar measurements: surface clutter, effects of cross-polarization, nonuniform beam filling and mispointing errors. Given its modular structure, the simulator allows the easy investigation of different orbits, scanning geometries and radar layouts, thus enabling comparisons among a variety of configurations. In the set-up currently proposed for the Earth Explorer 11, results based on a single global model output simulation demonstrate that the science requirements for the mission (accuracy of the line of sight winds of less than 1.4 m/s) can be achieved.