SAR ice thickness mapping in the Beaufort Sea using wave dispersion in pancake ice

The polar regions are distinctly different from other geographic areas and share a common set of characteristics, including remoteness; limited accessibility; low population densities; sensitive ecosystems of global importance; and increasing economic activity. In recent years, the uniqueness of these polar regions and their importance to the world has been recognized. This is made more urgent by the fact that the Arctic is warming much more rapidly than other regions of the world, and the summer sea ice is thinning and shrinking significantly. Such physical change can best be monitored by remote sensing from space. Although a number of satellite derived approaches exist, they need to be adapted to the new generation of sensors and the data provided need to be further validated by ground truth. The early autumn voyage of RV Sikuliaq to the southern Beaufort Sea (Oct-Nov 2015) and the PIPERS winter cruise in the Ross Sea (May-Jun 2017), offered very favorable opportunities for observing the properties and thicknesses of frazil-pancake ice types. The operational regions were overlaid by a dense network of retrieved satellite imagery, including SAR (synthetic aperture radar) imagery from Sentinel-1 and COSMO-SkyMed (CSK). This enabled us to fully test and apply the SAR- waves technique, first developed by Wadhams and Holt (1991), and experimentally verified by Wadhams et al. (2004) for deriving the thickness of frazil-pancake icefields from changed wave dispersion. A line of sub-images from a main SAR image is analysed running into the ice along the main wave direction. Each sub-image is spectrally analysed to yield a wave number spectrum, and the change in the shape of the spectrum between open water and ice, is used to retrieve frazil-pancake ice thickness. For each of the case studies considered here, there was good or acceptable agreement on thickness between the extensive in situ observations and the SAR-wave calculation