资源环境科技发展态势分析平台

The forthcoming Surface Water and Ocean Topography (SWOT) satellite mission will provide global measurements of the free surface of large rivers, providing new opportunities for remote sensing-derived estimates of river discharge in gaged and ungaged basins. SWOT discharge algorithms have been developed and benchmarked using synthetic data but remain untested on real-world swath altimetry observations. We present the first discharge estimates from AirSWOT, a SWOT-like airborne Ka-band radar, using 6 days of measurements over a 40-km segment of the Willamette River in Oregon, USA. The three evaluated discharge algorithms estimated discharge with normalized root-mean-square errors of 10-31% when compared with in situ gage data but were sensitive to an initial estimate of mean annual discharge. Our results show that these discharge algorithms provide reliable discharge estimates on remotely sensed data at SWOT-like spatial scales while highlighting the need for further algorithm sensitivity tests.

Plain Language Summary River discharge is a key element of the water cycle, but river gaging networks have significant gaps at the global scale. In 2021, the Surface Water and Ocean Topography (SWOT) mission will be launched to collect high-accuracy measurements of the world's surface waters, including all global rivers wider than 100 m. In anticipation of SWOT, methods to estimate discharge from its measurements have been developed but have yet to be tested on real-world data at the spatial scales and accuracies expected of SWOT. We test three such discharge algorithms on data collected by AirSWOT, an airborne variant of SWOT, as it flew over the Willamette River in Oregon, USA. We show that river discharge can be estimated by these algorithms with encouraging accuracy (10-31%) using only airborne measurements and a model-derived estimate of the mean annual discharge. We stress the need for further testing of these algorithms to determine their sensitivities to the initial estimate of flow and the hydraulic character of the river reach but suggest that these results are encouraging for future global-scale deployment of SWOT discharge algorithms.