| Title | A revised calibration of the interferometric mode of the CryoSat-2 radar altimeter improves ice height and height change measurements in western Greenland |
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| Author | Gray, L; Burgess, D ; Copland, L; Dunse, T; Langley, K; Moholdt, G |
| Source | The Cryosphere 11, 2017 p. 1041-1058, https://doi.org/10.5194/tc-11-1041-2017  Open Access |
| Image |  |
| Year | 2017 |
| Alt Series | Earth Sciences Sector, Contribution Series 20160331 |
| Publisher | Copernicus GmbH |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Nunavut |
| NTS | 48E/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 |
| Area | Devon 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 |
| Subjects | surficial geology/geomorphology; geophysics; Nature and Environment; glaciology; icefields; glaciers; ablation; glacial lakes; remote sensing; satellite imagery; radar imagery; radar methods; SARS;
Methodology |
| Illustrations | tables; location maps; satellite images; graphs; histograms |
| Program | Climate Change Geoscience Essential Climate Variable Monitoring |
| Program | Polar Continental Shelf Program
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| Released | 2016 12 21 |
| Abstract | We 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. |
| GEOSCAN ID | 299672 |
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