The water cycle is unarguably one of the most important aspects of Earth science for human society and the global environment. Just as clear is the importance of space missions for monitoring the Earth system. Radar is a powerful measurement technique, and is sensitive to water in all its phases: vapour in the atmosphere and liquid or frozen water at the surface. Space radar has so far been limited to low Earth orbit, which imposes significant limits on temporal sampling so that we know relatively little about processes on timescales less than a few days. Scientists are increasingly recognising the need for improved temporal sampling, and this presentation discusses what we are learning about using radar from geosynchronous orbit (GEO). GEO radar offers a transformation in our ability to observe the water cycle, down to timescales of minutes (at km resolution) to a few hours (sub-50 m). A radar in GEO has a permanent view across continental scales and becomes a programmable observatory able to serve a wide range of Earth science disciplines and lay the foundation for future operational services. We believe it will lead to notable advances in understanding of the water cycle, to improve fine resolution short-term weather forecasting, for better modelling of water resources, improvements in agriculture, and almost as a by-product it enables timely imaging in case of natural disasters from floods to volcanoes. This is an exciting mission concept to work on, one with the potential to transform how we observe Earth from space.

Steve Hobbs leads Cranfield University’s Space Group and is PI for Hydroterra – one of three candidates for ESA’s 10th Earth Explorer mission. Steve works at Cranfield University in the UK, and has been involved in its space engineering teaching and research since the early 1990s. Cranfield is a wholly postgraduate university specialising in aerospace and sectors including energy, manufacturing, and agriculture, and works closely with industry. Steve teaches for the MSc in Astronautics and Space Engineering, one of the UK and Europe’s leading postgraduate courses in space engineering. For over 10 years, geosynchronous radar has been one of his main research areas and he has contributed to developing the concept, especially for water cycle science. His technical training is in maths and physics (at Cambridge) and then doctoral research in instrumentation and micrometeorology (at Cranfield) – he has a PhD in kites from this work. From using radar to track insect migration he moved to using spaceborne radar more generally, and has contributed to research in mission design as well as specific radar applications – generally for land surfaces. In 2018 he led the team proposing a geosynchronous radar for ESA’s 10th Earth Explorer mission: Hydroterra (then called G-CLASS) was selected and is now one of three candidates in competitive Phase 0 study. Cycling and running help keep him sane, along with family currently spread from Scotland to the south of France.