DOI: 10.5061/dryad.vq83bk3sc
title: GNSS uplift time series and ice surface elevation changes

description: We use Global Navigation Satellite System (GNSS) stations attached to
 bedrock to measure elastic displacements of the solid Earth caused by
 dynamic thinning near the glacier terminus. When we compare our results
 with discharge, we find a time lag between glacier speedup/slowdown and
 onset of dynamic thinning/thickening. Our results show that dynamic
 thinning/thickening on Jakobshavn Isbræ occurs 0.87 ± 0.07 years before
 speedup/slowdown. This implies that using GNSS time series we are able to
 predict speedup/slowdown of Jakobshavn Isbræ by up to 10.4 months. For
 Kangerlussuaq Glacier the lag between thinning/thickening and
 speedup/slowdown is 0.37 ± 0.17 years (4.4 months).
description: <strong>GNSS data:</strong> To
 estimate GNSS site coordinates, we use the Gipsy X software package
 version GipsyX-1.3 developed at the Jet Propulsion Laboratory (JPL) and
 released in December 2019. We use JPL final orbit products which include
 satellite orbits, satellite clock parameters, and Earth orientation
 parameters. The orbit products take the satellite antenna phase center
 offsets into account. The atmospheric delay parameters are modeled using
 the Vienna Mapping Function 1 (VMF1) with VMF1grid nominals. Corrections
 are applied to remove the solid Earth tide and ocean tidal loading. The
 amplitudes and phases of the main ocean tidal loading terms are calculated
 using the Automatic Loading Provider
 (http://holt.oso.chalmers.se/loading/) applied to the FES2014b ocean tide
 model, including correction for center of mass motion of the Earth due to
 the ocean tides. The site coordinates are computed in the IGS14
 frame. <b>Airborne and satellite Laser
 Altimetry</b> We use repeat laser altimetry
 surveys from NASA’s Airborne Topographic Mapper (ATM) flights during 2006
 to 2019 (Studinger, 2014) to estimate annual ice elevation changes during
 April 2007- April 2020. The airborne altimetry measurements over the ice
 were conducted from March to May during annual campaigns as part of NASA’s
 Operation IceBridge. NASA ended its Operation IceBridge measurement
 over Greenland in spring 2019. To assess ice surface
 elevation changes during 2019-2020, we use Land Ice Along-Track Height
 Product (ATL06) from ICESat-2 (Ice, Cloud, and land Elevation Satellite 2)
 launched on 15 September 2018, as part of NASA's Earth Observing
 System (Smith et al., 2020). To estimate elevation changes from 2019 to
 2020, we use surface elevations from January to mid-May for 2019 and
 difference with surface elevations from January to mid-May for
 2020.
description: Annual elevation changes are provided in UTM zone 22 coordinates.
 The third column in each file show ice surface elavation change (m/yr).
 UTM coordinates are provided in Easting (meter), Northing (meter) in
 meters. Example of data file: #
 Elevation change between 2013 and 2014 using NASA’s Airborne Topographic
 Mapper (ATM) flights.<br> # UTM zone 22<br> easting  
 northing       dh<br>    m         m          m/yr<br>
 529805.00 7635257.00   -0.578<br> 529804.00 7635172.00   
 0.170 GNSS uplift time series are provided as weekly
 solutions. The data files contain five columns. column
 1: time in years. column 2: uplift in mm (weekly
 solution). column 3: standars deviation of weekly
 solution. column 4: SMB induced elastic uplift in
 mm column 5: standars deviation in mm of SMB induced
 elastic uplift