Long term sea-ice thickness record from satellite altimeters: Towards
global sea-ice volume estimates from space and application to climate
change studies.
Abstract
Sea ice plays a crucial role on the ocean and is one of the most
sensible indicators of climate change (IPCC 2013). The changing sea ice
can be characterized by 4 Essential Climate Variables (ECVs) identified
by the World Meteorological Global Organization Climate Observing System
implementation plan (WMO Pub No.GCOS-200) : 1) sea ice extent, 2) sea
ice concentration, 3) sea ice drift and 4) sea ice thickness. Since the
70ies, these 3 first variables are fairly well observed from space.
However, before 2010 and the launch of CryoSat-2, sea ice thickness
observations remain sparse and un- homogeneously distributed over time
and space. In the Arctic ocean, we will show in this presentation that
sea ice thickness time series can be extended to at least 16 years
(2002-2017) using Envisat, CryoSat-2 and Sentinel-3 satellites with
inter-missions biases calibrated and corrected. Among all potential
inter-mission biases, the most impacting is certainly the transition
from Low Resolution Mode (LRM) to Synthetic Aperture Radar (SAR)
altimetry. This transition is particularly important over sea ice
considering that the strong roughness heterogeneity, at basin scale and
within the radar footprint, has different signatures in LRM and SAR
modes. Here, we will focus on the transition between Envisat and
CryoSat-2 common flight period (20010-2012). Results are validated
against in situ observations (mooring, airborne, buoys and laser
altimetry). This same methodology is applied to produce equivalent long
term time series over Antarctica (2002-2017). In the southern ocean, the
main difficulties rely on the severe lack of in-situ observations and on
the ability to retrieve the snow depth. First results based on the Saral
and Cryosat Ka-Ku frequency radar differences will be shown. Finally, we
explain how this new global sea ice volume changes will provide new
insights on the response to climate change. In particular, the final
objective is to revisit the ocean freshwater budget and to provide a new
constraint on the land ice melt contribution to sea level rise that is
independent from the NASA Gravity Recovery and Climate Experiment
measurements.