Estimating River Discharge With Swath Altimetry: A Proof of Concept Using AirSWOT Observations

Abstract

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.