. Constraining Sediment Fluxes in Remote Fluvial Environments Using Experimental Geodetic and UAV Techniques

Abstract
Large increases in meltwater production and enhanced surface runoff at the Greenland Ice Sheet have resulted in increased mass loss into the global oceans. Increasing rates of meltwater and surface runoff also affects sediment transport. Huge quantities of sediment are being transferred from under the ice sheet into fluvial and fjord environments and eventually out onto the marine continental margin. Changing sediment transport patterns affect water and silt storage within fluvial systems as well as constituting an as yet undefined mass transfer from the ice sheet to the ocean. However, due to the remote nature of Greenlandic rivers an accurate record of sediment transport remains elusive. The Willis Research Group at the Earth Science Observation Center (ESOC) is currently investigating how sediment influences both remote sensing and geodetic observations to determine whether these techniques can capture sediment movement. We have two key objectives, the first to explore the potential of the ICESat-2 photon counting LiDAR to measure river suspended sediment concentrations (SSC) and the second to identify the effects of increased sediment deposition in rivers in southwestern Greenland on geodetic measurements. To establish whether ICESat-2 can record SSC we will conduct experiments at western Colorado rivers using in situ LiDAR with the same green frequency as that found on ICESat-2 to determine the empirical relationship between LiDAR backscatter flux patterns and suspended sediment. We will then apply this empirical relationship to ICESat-2 and test its validity. We will use UAV mounted infrared LiDAR and photogrammetry to calculate stage heights and the surrounding topography. If successful this will provide, for the first time, a regularly sampled remote sensing record of SSC and near-surface topography within rivers. Our second objective focuses on exploring whether bedrock motions of global positioning system (GPS) sites are affected by high sediment fluxes in fluvial systems. We concentrate initially on the Kangerlussuaq fluvial system in southwestern Greenland which has a long record of in-situ and geodetic observations. We use remote sensing platforms such as WorldView, Landsat and MODIS and digital elevation models (DEMs) from ArcticDEM to generate a sediment mass transfer timeseries. This mass change timeseries will be used, along with crustal models to determine the predicted response of the crust surrounding the GPS site to sediment mass changes alone. We will correlate this to the existing GPS record to elucidate the extent to which sediment contributes to GPS positions. Current measurements of ice mass loss include both sediment and ice mass transfer due to the coarse resolution of the Gravity Recovery and Climate Experiment (GRACE). By determining the influence of sediment mass changes on GPS we aim to highlight the extent to which sediment contaminates these GRACE estimates and thus inform future calculations of ice mass loss. Determining sediment transport characteristics will not only improve geodetic observations, but also enable greater planning for sediment resource management which is rapidly becoming a sought after resource.