DOI: 10.5285/e1d182b1-6aa6-434e-9390-f7956227cb82
title: Double-difference TerraSAR-X interferograms and derived grounding lines at the grounding line of the Kamb and Whillans Ice Streams, West Antarctica, 2012-2023

description: This dataset includes double-difference interferograms derived from TerraSAR-X synthetic aperture radar data acquired at the grounding line downstream of Engelhardt Subglacial Lake on the Gould Coast, Antarctica, in September 2012, April 2016, July 2023 and October 2023. The September 2012, July 2023 and October 2023 interferograms were generated by Oliver J. Marsh (British Antarctic Survey) using the Gamma Remote Sensing software and geocoded with the Bedmap2 DEM. The April 2016 interferogram was generated by Dana Floricioiu (DLR, German Aerospace Center) using DLR's Integrated Wide Area Processor (IWAP; Rodriguez et al, 2013). The image processing information, acquisition time and coincident modelled tide heights for all data used to derive the TerraSAR-X interferograms are provided in the lineage section. 

For each interferogram (September 2012, April 2016, July 2023 and October 2023) we provide a shapefile of the derived grounding line, which was manually traced along the landward boundary of the dense fringe belt associated with the vertical tidal motion of the ice (Point F). 

This dataset was produced as part of the study: Freer et al. (2024) Synchronous lake drainage and grounding line retreat at Engelhardt Subglacial Lake, West Antarctica. Journal of Geophysical Research: Earth Surface. 

Funding: 
Bryony I. D. Freer (project lead) was supported by Natural Environment Research Council (NERC) Satellite Data in Environmental Science (SENSE) Centre for Doctoral Training (grant no. NE/T00939X/1). Dana Floricioiu (dataset creator) was supported by DLR's Polar Monitor II and Antarctic Ice Sheet CCI projects (ESA/Contract No. 4000126813/18/I-NB). Images were acquired under DLR TerraSAR-X science data proposal HYD3673 (PI Dana Floricioiu).
description: TerraSAR-X data were acquired in SLC format with 11-day separation between pairs. Images were co-registered using speckle tracking with 512 x 512 windows with the secondary image then resampled to the reference image. Interferograms were calculated with 4 x 4 multilooking. Baselines were derived from satellite orbital parameters and flat-Earth phase contribution removed. Adaptive spectral filtering was applied to remove noise. Interferograms were geocoded to BEDMAP-2 surface topography (Fretwell et al., 2013) downsampled to 8 m grid, using a bicubic spline.

The derived grounding line for each interferogram were manually traced along the landward boundary of the dense fringe belt associated with the vertical tidal motion of the ice (Point F; c.f. Rignot, 1996; Rignot et al., 2011). For the April 2016 interferogram, an additional grounding line was traced at the inland limit of the weaker fringes that indicates ephemeral grounding over the ice plain further inland (id=2).

*** Image processing information and acquisition time for all TerraSAR-X double-difference interferograms ****
The tidal heights for each individual pass were calculated at [83.161degS, 160.5deg;W] using the CATS2008 model (Howard et al., 2019), corrected for the inverse barometer effect (IBE) using the daily air pressure values from the National Center for Environmental Prediction and the National Center for Atmospheric Research Reanalysis (NCEP/NCA). The expected vertical height difference for each interferogram is calculated using the tides from individual passes: [t2-t1] + [t3-t2]. 

DInSAR date: 
***September 2012:
 - Spatial resolution [m] (ground range x azymuth): 2.5 x3.3 (4x4 multilooking)
 - DEM for geocoding: Bedmap2 (8 m grid)
 - Pass date/time / tide height, corrected IBE [m]
 * t1: 2012-09-02 14:38:00 / -0.349
 * t2: 2012-09-13 14:38:00 / -0.507
 * t3: 2012-09-24 14:38:00 / +0.206
 - Expected height difference [m] [t2-t1] + [t2-t3]: -0.872


***April 2016:
 - Spatial resolution [m] (ground range x azymuth): 2.5 x3.3 (4x4 multilooking)
 - DEM for geocoding: Bedmap2 (8 m grid)
 - Pass date/time / tide height, corrected IBE [m]
 * t1: 2016-04-08 14:47:00 / -0.460
 * t2: 2016-04-19 14:47:00 / -0.076
 * t3: 2016-04-30 14:47:00 / -0.372
 - Expected height difference [m] [t2-t1] + [t2-t3]: +0.679

***July 2023:
 - Spatial resolution [m] (ground range x azymuth): 2.5 x3.3 (4x4 multilooking)
 - DEM for geocoding: Bedmap2 (8 m grid)
 - Pass date/time / tide height, corrected IBE [m]
 * t1: 2023-06-27 06:31:00 / -0.259
 * t2: 2023-07-08 06:31:00 / +0.023
 * t3: 2023-07-19 06:31:00 / +0.139
 - Expected height difference [m] [t2-t1] + [t2-t3]: +0.166

***October 2023:
 - Spatial resolution [m] (ground range x azymuth): 2.5 x3.3 (4x4 multilooking)
 - DEM for geocoding: Bedmap2 (8 m grid)
 - Pass date/time / tide height, corrected IBE [m]
 * t1: 2023-10-03 06:48:00 / -0.608
 * t2: 2023-10-14 06:48:00 / -0.359
 * t3: 2023-10-25 06:48:00 / -0.802
 - Expected height difference [m] [t2-t1] + [t2-t3]: +0.691

Data are provided in the WGS1984 geographic Coordinate system (EPSG:4326).
description: TerraSAR-X satellite mission data (operating on TSX-1 and TDX-1 satellites)
Gamma Remote Sensing software 
DLR's processing chain for the Grounding Line Location (GLL) parameter of Antarctic Ice Sheets cci project (Muir et al., 2020)
description: Resolution of the dataset:

** September 2012:
- Pixel resolution [m]: 20
- Spatial resolution (range) [m]: 2.5
- Spatial resolution (azimuth) [m]: 3.3

** April 2016:
- Pixel resolution [m]: 4.72
- Spatial resolution (range) [m]: 2.5
- Spatial resolution (azimuth) [m]: 3.3

** July 2023:
- Pixel resolution [m]: 8
- Spatial resolution (range) [m]: 2.5
- Spatial resolution (azimuth) [m]: 3.3


** October 2023:
- Pixel resolution [m]: 8
- Spatial resolution (range) [m]: 2.5
- Spatial resolution (azimuth) [m]: 3.3

Please note that the 2012 and 2016 interferograms were processed in a slightly different way to the July/Oct 2023 interferograms which is why the colour ramps appear slightly differently but this does not affect the data.