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).

SWOT于2022年12月16日发射，是全球首款星载二维条带测高卫星。在轨调试完成后，该卫星经历了一段校准与验证（cal/val）阶段。此校准验证阶段于2023年3月29日至7月10日开展，期间卫星采用单日重复轨道，覆盖范围有限，涵盖布里斯托尔湾（Bristol Channel）与塞文河口及河流区域。SWOT-UK项目是一项原位与机载数据采集及多学科研究计划，以布里斯托尔湾和塞文河河口区域为研究核心，作为英国对国际SWOT科学团队验证工作的贡献项目。
SWOT-UK项目的目标之一是向科学界分享增值验证数据集。研究团队为布里斯托尔湾及塞文河口河流区域共组装了总计17个测点的地面真值水位数据集。这些数据来源于英国环境署（Environment Agency）与区域海岸监测计划国家网络（海峡海岸观测站，Channel Coastal Observatory）的应用程序接口（API），同时项目团队额外布设了3套全球导航卫星系统干涉反射测量（GNSS-IR）系统。鉴于该项目同时旨在验证冰冻卫星2号（CryoSat-2）数据以与SWOT数据开展对比，研究团队收集了2012年1月至2023年7月期间可获取的水位计数据。借助英国地形测量局（Ordnance Survey）提供的软件工具，研究人员将所有数据转换至ETRS89（WGS84）椭球坐标系，以匹配卫星测高数据的坐标基准。对于以海图基准面或水位基准面为参照的测站，研究人员先将其校正至英国地形测量局基准面（Ordnance Datum），再完成ETRS89（WGS84）坐标系转换。