Global River Radar Altimetry Time Series (GRRATS): new river elevation earth science data records for the hydrologic community

Stephen Coss,Tamlin Pavelsky,Qi Guo,Yuanyuan Jia,Stephen Tuozzolo,Michael Durand,George H Allen,C K Shum,Yuchan Yi,Stéphane Calmant

doi:10.5194/essd-12-137-2020

Abstract

Abstract. The capabilities of radar altimetry to measure inland water bodies are well established, and several river altimetry datasets are available. Here we produced a globally distributed dataset, the Global River Radar Altimeter Time Series (GRRATS), using Envisat and Ocean Surface Topography Mission (OSTM)/Jason-2 radar altimeter data spanning the time period 2002–2016. We developed a method that runs unsupervised, without requiring parameterization at the measurement location, dubbed virtual station (VS) level, and applied it to all altimeter crossings of ocean-draining rivers with widths >900 m (>34 % of the global drainage area). We evaluated every VS, either quantitatively for VS locations where in situ gages are available or qualitatively using a grade system. We processed nearly 1.5 million altimeter measurements from 1478 VSs. After quality control, the final product contained 810 403 measurements distributed over 932 VSs located on 39 rivers. Available in situ data allowed quantitative evaluation of 389 VSs on 12 rivers. The median standard deviation of river elevation error is 0.93 m, Nash–Sutcliffe efficiency is 0.75, and correlation coefficient is 0.9. GRRATS is a consistent, well-documented dataset with a user-friendly data visualization portal, freely available for use by the global scientific community. Data are available at https://doi.org/10.5067/PSGRA-SA2V1 (Coss et al., 2016).

Highlights

Despite growing demand from emerging large-scale hydrologic science and applications, global and freely available observations of river water levels are still scarce (Hannah et al, 2011; Pavelsky et al, 2014; Shiklomanov et al, 2002)
Evaluation of these global river elevation models requires global datasets of river elevation time series, but in situ river water levels are scarce, as they are often not shared outside specific government agencies
The 39 Global River Radar Altimetry Time Series (GRRATS) rivers account for 50 million km2 (> 34 %) of the global drainage area and include 13 Arctic rivers

Summary

Introduction

Despite growing demand from emerging large-scale hydrologic science and applications, global and freely available observations of river water levels are still scarce (Hannah et al, 2011; Pavelsky et al, 2014; Shiklomanov et al, 2002). Advances in remote sensing and computing capabilities have enabled new areas of global fluvial research that are dependent upon river elevations, including global hydrologic quantification of carbon and nitrogen fluxes (e.g., Allen and Pavelsky, 2018; Oki and Yasuoka, 2008) and characterization of flood risk for future climate scenarios (Schumann et al, 2018; Smith et al, 2015) Evaluation of these global river elevation models requires global datasets of river elevation time series, but in situ river water levels are scarce, as they are often not shared outside specific government agencies. Coss et al.: Global River Radar Altimetry Time Series (GRRATS)

Methods

Results

Conclusion