Algorithm for validation of sea ice concentration
Full document (pdf file)
Philosophy
We choose not to construct intermediate level products on a refined resolution; i.e. we integrate and average, rather than interpolate and extrapolate.
Starting point
A sea ice concentration (SIC) analysis is available at a very high spatial resolution as an ice chart, with this discrete set of values:
| Class | Values | Mapping |
|---|---|---|
| Open water | <0.1 | 0.0 |
| Very open drift ice | 0.1, 0.2, 0.3 | 0.2 |
| Open drift ice | 0.4, 0.5, 0.6 | 0.5 |
| Close drift ice | 0.7, 0.8 | 0.75 |
| Very close drift ice | 0.9, 1.0 | 0.95 |
| Fast ice | 1.0 | 1.0 |
Model results are available at an intermediate spatial resolution, using a continuous set of values in the range 0.0-1.0; Fast ice is not modeled. The model assimilates SIC, but presently, the data being assimilated are independent from the data used in the ice chart analysis.
Implementation
SIC ice chart data are available with a resolution that is order of 10x finer than the model product, so SIC from the ice chart analysis is mapped onto the model product grid, and averaged over each model grid cell.
Both of these coarse resolution product are categorized into the discrete set of classes used in the ice chart analysis, but the Fast ice category is discarded, and Fast ice values in the ice chart analysis are re-set to the class 0.9-1.0/Very close drift ice.
Validation products
- Time series for SIC root-mean-square
- Histograms for the SIC classes Very open drift ice, Open drift ice, Close drift ice and Very close drift ice (frequency in ice chart, frequency in model, frequency of overlapping in ice chart & model)
- Maps of sea ice classes