Wind-wave attenuation under sea ice in the Arctic: a review of remote
sensing capabilities
Abstract
Wind-generated waves strongly interact with sea ice and impact air-sea
exchanges, operations at sea, and marine life. Unfortunately, the
dissipation of wave energy is not well quantified and its possible
effect on upper ocean mixing and ice drift are still mysterious. As the
Arctic is opening up and wave energy increases, the limited amount of
\emph{in situ} observations is a clear limitation to
our scientific understanding. Both radar and optical remote sensing has
revealed the frequent presence of waves under the ice, and could be used
more systematically to investigate wave-ice interactions. Here we show
that, in cloud-free conditions, Sentinel-2 images exhibit brightness
modulations in ice-covered water, consistent with the presence of waves
measured a few hours later by the ICESat-2 laser altimeter. We also show
that a full-focus SAR processing of Sentinel-3 radar altimeter data
reveals the presence of waves under the ice and their wavelengths,
within minutes of Sentinel-2 imagery. The SWIM instrument on CFOSAT is
another source of quantitative evidence for the direction and
wavelengths of waves under the ice, when ice conditions are spatially
homogeneous. In the presence of sea ice, a quantitative wave height
measurement method is not yet available for all-weather near-nadir radar
instruments such as altimeters and SWIM. However, their systematic
co-location with optical instruments on Sentinel-2 and ICESat-2, which
are less frequently able to observe waves in sea ice, may provide the
empirical transfer functions needed to interpret and calibrate the radar
data, greatly expanding the available data on wave-ice interactions.