Coastal sea-level in Norway from CryoSat-2 SAR altimetry

Conventional spaceborne altimeters determine the sea surface height with an accuracy of a few centimeters. Although satellite altimetry may be regarded as a mature technology, altimeter observations collected over coastal regions suffer from numerous effects which degrade their quality. For example, land and bright targets contaminate the radar footprint, and the range and geophysical corrections (wet troposphere, tides, and high-frequency atmospheric and ocean signals) are notoriously difficult to model in the coastal zone.

The Norwegian coast adds further complications, due to the many islands, mountains, and deep, narrow fjords. As the first of its kind, the European Space Agency's CryoSat-2 satellite carries a Synthetic aperture Interferometric Radar ALtimeter (SIRAL) which can operate in Synthetic Aperture Radar (SAR), SAR Interferometric (SARIn), as well as conventional Low Rate (LR) modes.

When operating in SARIn mode, the altimeter measures the phase difference of the backscattered signal at two antennas, from which the position of any backscattered point may be derived. Thus, the SARIn mode may help discriminating and mitigating land contamination signals from off-nadir land targets (e.g., steep cliffs) over coastal regions.

Conventional altimetry (Envisat, Jason-2) and specific coastal products (CTOH, PISTACH) have recently been tested along the Norwegian coast, where it was concluded that the coastal products did not offer an improvement over the conventional products they are based on. We therefore investigate the potential for CryoSat-2 data to provide improved ocean measurements in the Norwegian coastal zone.

In particular, we make use of CryoSat-2's SAR and SARIn modes and determine coastal sea surface heights in specific coastal regions, and compare results with independent sea-level observations.