Hydroterra+: an EO mission concept to reveal sub-daily water processes

Much of the change that our planet will experience in the coming decades is driven by climate. In this ever‑warming world, water is of central importance, and Hydroterra+ is an ESA mission concept designed to fill key observation gaps and improve our understanding of the water cycle and water management.

Hydroterra+ focuses primarily on the Mediterranean basin, identified as a climate‑change hotspot due to its transitional position between subtropical and mid‑latitude zones, and sub‑Saharan Africa, one of the regions most affected by increasing climate shocks. The mission also foresees the possibility of monitoring specific areas on an hourly basis, for example in emergency situations or for dedicated scientific studies.

The mission is based on a geostationary Synthetic Aperture Radar (SAR) operating in interferometric mode. Its near‑continuous observation capability, short revisit time, and very wide coverage make Hydroterra+ uniquely suited to monitor water‑related processes on timescales of hours at regional scale. Existing and planned low‑Earth‑orbit missions are poorly matched to this need.

Hydroterra+ will provide a suite of sub‑daily products, including:

• Integrated Water Vapour (IWV) to improve understanding and forecasting of extreme weather events;
• Surface Soil Moisture (SSM) to advance knowledge of soil dynamics and related processes, including agricultural practices;
• Snow Water Equivalent (SWE) and Snow Melt Phases (SMP) to improve understanding of mid‑latitude cryosphere processes;
• Surface Displacements (DQ) and Change Maps (CM) to enhance knowledge of geophysical hazards.

Hydroterra+ is an Earth Explorer 12 candidate mission and is currently progressing through Phase‑0 studies. This paper will present the mission concept and the first results of its feasibility analysis, including outcomes from several Observing System Simulation Experiments (OSSEs) conducted across the scientific mission domains.