Measuring the winter sea level in the Arctic coastal domain with CryoSat-2 SARIn mode: potential and limitations

Abstract:

For several decades, remote sensing observations have shown a rapid reduction of the ice-covered area and thinning of the ice in the Arctic Ocean^1,2. Besides the scientific interest as climate indicators, knowledge of sea ice and ocean dynamics is important for the shipping and fishery industries. Being the natural interface between the oceans and humans, the coastal zone is also where changes in the sea level and the sea ice thickness have the largest impact on human society³.

In the last 25 years, satellite radar altimetry has been used to monitor the polar oceans. Despite recent improvements in coastal altimetry, coastal sea level estimates in ice-covered regions are still extremely sparse, due to the technical challenges faced by altimetry in coastal regions³, and because the density of measurements is determined by the number and spatial distribution of leads. As the temporal and spatial scales of physical processes decrease in the coastal domain³, the low availability of winter sea surface estimates limits our knowledge of seasonal ocean physical processes as well as it casts large uncertainty on sea ice thickness estimates.

Along the Arctic coastline, ESA’s CryoSat-2 (CS2) satellite radar altimetry mission operates in SAR Interferometric (SARIn) mode. Using the phase information available in this mode has been suggested to provide more accurate sea level estimates in ice-covered regions, and with a lower uncertainty, than regular SAR mode, due to the ability to correct for off-nadir ranging to leads⁴.

This work assesses the potential and limitations of the CS2 SARIn mode in the Arctic coastal domain by applying a novel multi-peak processing technique⁵ to SARIn waveforms, which further increases the number of valid sea surface retrievals in ice-covered regions. Results are compared with sea level estimates from the NASA ICESat-2 mission, flying a very high resolution (~17 m) photon counting green laser able to measure closer to the coast than ever possible before with satellite altimetry. A denser sampling of the winter sea level in ice-covered regions along the Arctic coastline has the potential to improve mean sea surface products as well as tide models relying on altimetry measurements—thus, to significantly benefit the retrieval of a large variety of geophysical quantities from altimetry in the coastal domain.