Water level data from the Bristol Channel and Severn Estuary and River region for validation of satellite altimeters, 2012-2023 (SWOT-UK project).

Launched 16 December 2022, SWOT is the first of its kind spaceborne 2D swath altimeter and, after commissioning, underwent a period of calibration and validation (cal/val). This cal/val period lasted from 29 March to 10 July 2023, with a daily repeat orbit of a limited coverage, which included the Bristol Channel and Seven Estuary and River region. The SWOT-UK project was a programme of in situ and airborne data collection, and multidisciplinary research, centred on the Bristol Channel and Severn River and Estuary region as the UK contribution to the international SWOT Science Team validation work. One of aims of the SWOT-UK project is to disseminate value-added validation datasets for use by the scientific community. A large dataset of ground-truth water level was assembled for the Bristol Channel and Severn Estuary and River region (seventeen sites in total). These data came from the Environment Agency and National Network of Regional Coastal Monitoring Programmes (Channel Coastal Observatory) APIs, with three addition Global Navigation Satellite Systems Interferometric Reflectometry (GNSS-IR) systems installed by the project team. As the project also aimed to validate CryoSat-2 data, for comparison with SWOT, the water level gauge data was obtained from January 2012 to July 2023, where available. These data were transformed to ETRS89 (WGS84) Ellipsoid using a software utility provided by the Ordnance Survey, for comparison to satellite altimetry data. Stations measuring relative to chart or stage datum were corrected to ordnance datum before transformation to ETRS89 (WGS84).