Abstract's details
A review of the current altimetry mission performances over the polar ice sheets: Cryosat-2, AltiKa and Sentinel-3A
CoAuthors
Event: 2017 Ocean Surface Topography Science Team Meeting
Session: Science IV: 25 years of satellite altimetry for Cryosphere and Hydrology: from experimental to emerging operational applications
Presentation type: Type Oral
Contribution: PDF file
Abstract:
Earth’s polar regions have been monitored near continuously by altimeter satellites for 30 years now. Thanks to their wide coverage and high temporal sampling, radar altimeters have greatly improved our knowledge of the ice-sheet topography and our understanding of the ice sheet dynamics. Until the 2010s, radar altimeters have been exclusively operating in the Ku-band, in Low Resolution Mode (LRM). This technique has been successfully exploited for oceanic surveys but suffers from several limitations over the polar ice sheets. The combined effects of surface roughness, surface slope and signal penetration into the snowpack affect the LRM measure in various ways.
A new promising generation of altimeter satellites has been launched in the last few years: Cryosat-2 (2010), Saral/Altika (2013) and Sentinel-3A (2016). Thanks to its Ka frequency, the penetration depth of the AltiKa signal in the snowpack is much smaller than usual Ku frequency radars. This property is supposed to facilitate the estimation of the ice sheet elevation at snow/air interface. In the same time, Cryosat-2 and Sentinel-3A carry a new generation of radar altimeter, operating in the innovative "Delay Doppler” mode (or SAR mode). This specific mode improves the along-track resolution to 300 meters, bringing valuable perspectives for the monitoring of ice-sheet surfaces.
The main objective of this presentation is to show a cross-comparison of the current altimetry missions over the polar ice sheets’ interior: Cryosat-2 (LRM, Ku-band), AltiKa (LRM, Ka-band) and Sentinel-3A (SARM, Ku-band). This work has been performed over one year of data in 2016/2017, corresponding to a common acquisition period for the three missions. Firstly, we will illustrate the measure sensitivity to the snowpack volume scattering by analyzing the waveform shapes. Secondly, we will assess the precision and accuracy of the surface elevation retrieved from the waveforms in comparison with laser altimetry data (ICESat), GNSS acquisitions and existing DEMs. Finally, we will present several key results showing the benefits brought by the SAR mode and the Ka-band for monitoring the polar ice sheets. The comparison is of interest in the context of the definition of a future cryosphere observation mission.
A new promising generation of altimeter satellites has been launched in the last few years: Cryosat-2 (2010), Saral/Altika (2013) and Sentinel-3A (2016). Thanks to its Ka frequency, the penetration depth of the AltiKa signal in the snowpack is much smaller than usual Ku frequency radars. This property is supposed to facilitate the estimation of the ice sheet elevation at snow/air interface. In the same time, Cryosat-2 and Sentinel-3A carry a new generation of radar altimeter, operating in the innovative "Delay Doppler” mode (or SAR mode). This specific mode improves the along-track resolution to 300 meters, bringing valuable perspectives for the monitoring of ice-sheet surfaces.
The main objective of this presentation is to show a cross-comparison of the current altimetry missions over the polar ice sheets’ interior: Cryosat-2 (LRM, Ku-band), AltiKa (LRM, Ka-band) and Sentinel-3A (SARM, Ku-band). This work has been performed over one year of data in 2016/2017, corresponding to a common acquisition period for the three missions. Firstly, we will illustrate the measure sensitivity to the snowpack volume scattering by analyzing the waveform shapes. Secondly, we will assess the precision and accuracy of the surface elevation retrieved from the waveforms in comparison with laser altimetry data (ICESat), GNSS acquisitions and existing DEMs. Finally, we will present several key results showing the benefits brought by the SAR mode and the Ka-band for monitoring the polar ice sheets. The comparison is of interest in the context of the definition of a future cryosphere observation mission.