Improved Inland Water Level Retrievals from CryoSat-2: Enhanced Spatial Coverage and Uncertainty Characterisation for Hydrological Applications

Accurate monitoring of inland water levels is essential for quantifying surface water storage, understanding hydrological extremes, and constraining hydrodynamic models through data assimilation. Satellite radar altimetry provides a unique long-term and global perspective on water surface height (WSH), yet its application over rivers and lakes remains challenging due to complex geometries, heterogeneous surface conditions, and limited characterisation of observation uncertainty. In the Cryo-TEMPO project, we present the Inland Water dataset delivering enhanced CryoSat-2 derived WSH products over lakes and rivers for the period 2011–2025. The processing relies on the CLS Data Handling and Processing System and integrates four retracking algorithms (OCOG, TFMRA, SAMOSA+, and MwAPP). Major advances rely on the improved spatial extraction of river observations using the global SWOT River Database (SWORD), combined with adaptive buffering. This increases the number of valid river measurements by up to a factor of five compared to previous baselines, while preserving physically consistent longitudinal water surface profiles over large river systems. A key innovation of the dataset is a new data-driven uncertainty estimation framework designed to support downstream applications, including hydrodynamic modelling and data assimilation. This approach at 20 Hz yields more representative and internally consistent uncertainty estimates, significantly reducing the occurrence of high-uncertainty outliers relative to earlier processing phases. Internal evaluation and external validation against in situ gauge records, ICESat-2 observations, and Hydroweb time series confirm good agreement for both lakes and rivers. Over rivers, OCOG and TFMRA retrackers provide the most robust results, while residual outliers are mainly associated with SARin measurements in complex or ice-affected regions. CryoSat-2, Satellite Altimetry, Inland Waters, Water Level, Hydrology