High-Latitude Multi-Altimeter Observations of the Arctic Ocean and its Sea Ice Cover

Author:

Sinead Farrell - (University of Maryland, College Park)

Co-Investigator(s):

Donghui Yi (Global Science & Technology, Inc.)
Kyle Duncan (University of Maryland, College Park)

Collaborator(s):

John Kuhn (NOAA, NESDIS/ORA)

Abstract:

Due to a phenomenon known as Arctic amplification, the Arctic is warming at twice the rate of global temperate rise. This increase in heat is impacting the Arctic climate system, which is experiencing widespread environmental change, including mass loss of the Greenland Ice Sheet, an accelerating decline in the Arctic sea ice cover, warming in the subpolar seas, and freshening of the Beaufort Gyre. Meanwhile we are currently experiencing a golden age in high-latitude altimetry that allows us to observe many of these changes.

Although spaceborne altimeters have offered some coverage of the polar oceans since the 1990s, their orbital inclinations limited observations to 81.5 N. It was only with the launch of a dedicated polar altimeter, NASA’s ICESat, that we achieved near-complete coverage, to 86 N. The ICESat altimeter system was however impacted by laser lifetime issues, and provided periodic coverage of the Arctic Ocean for a just few months per year between 2003 and 2009. This was followed in 2010 by the launch of ESA’s CryoSat-2, carrying the SAR/Interferometric Radar Altimeter (SIRAL), which has since proved to be a game-changer for high-latitude altimetry. Now operating for over 10 years and providing observations to 88 N, SIRAL data have been used to map the mean sea surface of the Arctic Ocean and its dynamic ocean topography, and have also revealed large interannual variability in Arctic sea ice thickness. In 2018, CryoSat-2 was joined by another dedicated polar altimeter, NASA’s ICESat-2, carrying the Advanced Topographic Laser Altimeter System (ATLAS). ATLAS offers unprecedented along-track resolution with year-round observations. These two polar altimeters are augmented by Ku-band radar altimeter data from the Sentinel-3A/B missions and Ka-band data from the CNES/ISRO SARAL/AltiKa satellite, delivering additional observational capability in the subpolar seas.

Together these five altimeters offer the unique opportunity to map the Arctic Ocean at a variety of sensor frequencies, and footprint resolutions, thereby providing a more complete picture of sea surface topography in both the open ocean and ice-covered waters. Our proposal will exploit multi-mission polar ocean altimetry to quantify recent changes in the Arctic Ocean and its ice cover. We will investigate variability in key climate parameters, including lead frequency, open water fraction and dynamic ocean topography. We will leverage improvements in tracking polar ocean surface topography for the derivation of a state-of-the-art mean sea surface model that will improve sea ice freeboard retrievals from ICESat-2. The proposed research is responsive to the A.14 solicitation, wherein we will produce the highest-quality satellite altimeter observations of Arctic Ocean topography and apply these data to address key questions in polar climate science. We directly address three of the four identified priority areas:

1. We will conduct a regional study of the Arctic Ocean that uses high-resolution merged altimetric data sets including NASA’s ICESat-2 and ESA’s CryoSat-2 to investigate polar ocean variability.
2. We will develop and evaluate new geophysical algorithms to improve the quality of polar ocean surface topography data, including contributing scientific analysis in preparation for the Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) mission, the next dedicated polar altimeter due for launch in 2027.
3. We will research and develop operational applications of polar altimetry for monitoring sea ice conditions in the Arctic Ocean and marginal ice zone in support of improving seasonal-to-interannual prediction of sea ice conditions.

The investigators seek to renew their membership of the Ocean Surface Topography Science Team (OSTST). The team have extensive knowledge of the combined use of satellite laser and radar altimetry for monitoring the polar ocean and the relevant experience to successfully conduct the proposed studies.

Supported by NOAA