Advanced gap-filling techniques for sea ice concentration climate data records

In the context of the OSI SAF Visiting Scientist Program, Courtenay Strong from the University of Utah, worked on Advanced gap-filling techniques for sea-ice concentration climate data records. This work took place in 2022 and was supervised by Thomas Lavergne and Steinar Eastwood (MET Norway).

Objectives and background of the study

The OSI SAF delivers sea-ice concentration products in Near Real Time as well as in the form of Climate Data Records (CDRs) starting in the late 1970s. These are processed from polar-orbiting passive microwave radiometers which generally do not observe all the way to the poles, leaving an Arctic “polar observation hole”. The traditional technique for filling this hole involves a spatial interpolation which can produce unrealistic artifacts, especially for larger holes and during summer and early fall when the sea-ice edge is at high latitudes. 

The objective of this project was to provide a more realistic fill based on a technique developed by Courtenay Strong and colleagues at the University of Utah. The method involves solving a partial differential equation within the hole using observations on its perimeter as boundary conditions. The fill also has a stochastic term that mimics the spatial scales of the sea ice concentration variability, and that is trained using observations outside the polar observation hole. In the example shown below, the observation hole for 18 July 1983 is shown by a red circle enclosing the traditional fill in the right panel. The left panel shows the same case with the new gap-filling technique applied. 

Report conclusions

The new gap-filling technique is effective in capturing the gradients and heterogeneity of Arctic sea ice concentrations based on tests of the method in synthetic circles placed outside the observation hole. By capturing these important properties of the sea ice, the new fill method provides a more realistic fill for the polar observation hole and was implemented in the SIC CDR Version 3 (OSI-450-a). The new technique also tested well in a feasibility study filling observation holes in fields of brightness temperature which vary with sea ice type/age.

Main recommendations from this study

Users needing sea ice concentration values with coverage over the polar observation hole are encouraged to use the fills produced by the new gap-filling technique, as included in SIC CDR v3 (OSI-450-a), as a more realistic alternative to results from the traditional interpolation method. Additionally, promising preliminary results on applicability of the method to fields related to sea ice type/age could be pursued as future work.

Benefits for the SAF

This data-driven gap-filling technique based on a partial differential equation provides the community with a realistic and objective solution to data coverage challenges near the pole. Availability of this new solution increases the SIC CDR v3 (OSI-450-a) ease of use, broadens its appeal to potential users in the research community, and facilitates comparisons against, e.g. modelled sea-ice cover. 

Report on this study

Advanced gap-filling techniques for sea-ice concentration climate data records

Authors

Courtenay Strong, University of Utah

Thomas Lavergne, MET Norway