Observing Outlet Glacier Motion Using High Rate GPS

Observations of short-term variations in the flow speed of marine-terminating outlet glaciers are essential for understanding the dynamics of these systems in relation to changes in surface melting and calving. Due to their inaccessiblity and highly crevassed and unstable surfaces, there is little existing ice motion data for polar outlet glaciers at high-temporal and spatial resolution over multi-week timescales. Here we present the results, successes, and planned improvements of a proof- of-concept study at Store Glacier,West Greenland in 2008 where we deployed both dual frequency and inexpensive L1 single frequency receivers. The dual-frequency system, was deployed roughly 15 km from the ice front near a large supraglacial lake and recorded at 1 s epochs. Three single frequency receivers, recording at 10 s epochs, were installed within 5 km of the ice front and transmitted their data to a base station on the side of the glacier. Dual frequency data was post processed using GAMIT's kinematic software package TRACK. However, multiple attempts at post processing the L1 phase data were unsuccessful due to multipath cycleslip intensity, massive clock drift, and data corruption, so that only the pseudorange data could be utilized. By combining the high-rate motion data with concurrent meteorology,time-lapse photography and seismographic data, we assess how variations in motion correspond with changes in meltwater production, calving and sea ice conditions at the front. Based on this initial deployment, we propose future improvements including increased data collection robustness, use of chokering antennae for multipath mitigation, broadcast GPS clock correction, and dual frequency disposable rover solutions for drastically improved positional analysis at the glacier front.