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TitleA revised calibration of the interferometric mode of the CryoSat-2 radar altimeter improves ice height and height change measurements in western Greenland
AuthorGray, L; Burgess, DORCID logo; Copland, L; Dunse, T; Langley, K; Moholdt, G
SourceThe Cryosphere 11, 2017 p. 1041-1058, Open Access logo Open Access
Alt SeriesEarth Sciences Sector, Contribution Series 20160331
PublisherCopernicus GmbH
Mediapaper; on-line; digital
File formatpdf
NTS48E/09; 48E/10; 48E/11; 48E/12; 48E/13; 48E/14; 48E/15; 48E/16; 48F/09; 48F/16; 48G/01; 48G/08; 48G/09; 48G/16; 48H
AreaDevon Ice Cap; Jakobshavn Glacier; Denmark; Greenland
Lat/Long WENS -85.0000 -80.0000 75.8000 74.8000
Lat/Long WENS -51.0000 -47.0000 71.2500 67.5000
Subjectssurficial geology/geomorphology; geophysics; Nature and Environment; glaciology; icefields; glaciers; ablation; glacial lakes; remote sensing; satellite imagery; radar imagery; radar methods; SARS; Methodology
Illustrationstables; location maps; satellite images; graphs; histograms
ProgramClimate Change Geoscience Essential Climate Variable Monitoring
ProgramPolar Continental Shelf Program
Released2016 12 21
AbstractWe compare geocoded heights derived from the interferometric mode (SARIn) of CryoSat to surface heights from calibration-validation sites on Devon Ice Cap and West Greenland. Comparisons are included for both the heights derived from the first return (the 'point-of-closest-approach' or POCA) as well as heights derived from delayed waveform returns ('swath' processing). While swath processed heights are normally less accurate than edited POCA heights, of order 1 - 5 m instead of order 1- 2 m, the increased coverage possible with swath data complements the POCA data and provides useful information for both system calibration and improving digital elevation models (DEMs). We show that the pre-launch interferometric baseline coupled with an additional roll correction (~0.0075°), or equivalent phase correction (~0.0435 radians), provides an improved calibration of the interferometric SARIn mode.
We extend the potential use of SARIn data by showing the influence of surface conditions, especially melt, on the return waveforms, and that it is possible to detect and measure the height of summer supraglacial lakes in West Greenland. A supraglacial lake can provide a strong radar target in the waveform, stronger than the initial POCA return, if viewed at near normal incidence. This provides an ideal situation for swath processing and we demonstrate height accuracies of ~ 0.5 m for two lake sites, one in the accumulation zone and one in the ablation zone, which were measured every year from 2010 or 2011 to 2016. Each year the lake in the ablation zone was viewed in June by ascending passes and then 5.5 days later by descending passes which allows an approximate estimate of the filling rate. The results suggest that CryoSat waveform data and measurements of supraglacial lake height change could complement the use of optical satellite and be helpful as proxy indicators for surface melt around Greenland.
Summary(Plain Language Summary, not published)
The CryoSat radar altimeter is a European Space Agency initiative that will play an integral role in Canada's scaled glacier-climate observing approach, contributing to Climate Change Geoscience Program objectives through provision of data on glacier mass change as it concerns freshwater flux to oceans. In this paper, improvements to the performance of CryoSat-2 are made through adjusting the pre-calibration roll angle and validating ice cap surface and near-surface interpretation of the radar waveforms. We show that CroSat-2 is effective for measuring height change of supraglacial lakes on Greenland as potentially useful indicators of climate change. Similar measurements will be made over Canadian ice caps in future studies.

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