Response to Variations in River Flowrate by a Spaceborne GNSS-R River Width Estimator

April Warnock,Christopher Ruf

doi:10.3390/rs11202450

Abstract

In recent years, the use of Global Navigation Satellite System-Reflectometry (GNSS-R) for remote sensing of the Earth’s surface has gained momentum as a means to exploit existing spaceborne microwave navigation systems for science-related applications. Here, we explore the potential for using measurements made by a spaceborne GNSS-R bistatic radar system (CYGNSS) during river overpasses to estimate its width, and to use that width as a proxy for river flowrate. We present a case study utilizing CYGNSS data collected in the spring of 2019 during multiple overpasses of the Pascagoula River in southern Mississippi over a range of flowrates. Our results demonstrate that a measure of river width derived from CYGNSS is highly correlated with the observed flowrates. We show that an approximately monotonic relationship exists between river flowrate and a measure of river width which we define as the associated GNSS-R width (AGW). These results suggest the potential for GNSS-R systems to be utilized as a means to estimate river flowrates and widths from space.

Highlights

Knowledge of river streamflow is crucial for a number of water-related applications
The Cyclone Global Navigation Satellite System (CYGNSS) mission is a Global Navigation Satellite Systems-Reflectometry (GNSS-R) bistatic radar system that was launched on 15 December 2016 and consists of eight microsatellites, each with a four-channel Global Positioning System (GPS) L1 coarse acquisition (C/A) radar receiver
The fitted power series for each of the overpasses is shown in Figure 5, where the observed signal at each tiFmigeursete5p. fFoitrteedacphowtrearckserisieps lfootrteedacihnobfltuhee, faivnedAthperilre2d01l9inPeasschaogwouslathoevepropwasesress,eursieinsgfiatted to the signatlhwresithhoilnd 2o2f %22%ofotfhteheppeeaakkaatsrtihveecructeonfftfeorr. tFhiegpuorreti6onshoof wthes wthaeverefosrumltstoobfethfiettelidn. ear regression between the associated GNSS-R width (AGW) and the observed Pascagoula flowrates

Summary

Introduction

Knowledge of river streamflow is crucial for a number of water-related applications. For example, streamflow information is needed for hydrological modeling, watershed management, flood monitoring and warning systems, and hydrodynamic power management. Existing Global Navigation Satellite System-Reflectometry (GNSS-R) systems present the potential for exploiting high-temporal-resolution data over large scales for use as inputs to flowrate algorithms, or as a means of developing a novel remote sensing signature for river properties (e.g., width) that correlate directly to streamflow. To investigate this potential, we used bistatic radar data from the NASA Cyclone Global Navigation Satellite System (CYGNSS) Mission to study the signal response to a range of flowrates over a segment of an uncontrolled river. Our results indicate that the river’s AGW is highly correlated with changes in its streamflow at high flowrates and stream heights (when the river can be expected to overspill its banks)

Methods

Results

Conclusion