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| Sea ice extent and concentration
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| Definition |
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Sea ice extent is the ocean area in which a defined minimum of sea ice can be found.
Sea ice concentration is the proportion of the ocean area actually covered by ice in the area of the total sea ice extent.
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| Rationale |
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Changes in sea ice concentration (extent) play a major role in ocean-atmosphere fluxes of heat, moisture, and momentum. Climate models predict major changes in ice cover for a doubling of CO2 levels with impacts on global climate and ocean thermohaline circulation. Ice concentration and extent are required to validate sea ice models and for change detection.
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| Users |
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GCM modellers, climate change detection analysts, and climate impact modelling/analysts.
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| Assessment method |
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Tiers 1-3: estimated from high-resolution remote sensing images;
Tier 5: passive microwave measurements, spectral radiance measurements, and microwave backscatter measurements.
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| Units of Measure |
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Concentration - Fractional coverage of total ice, km2.
Extent - Area within a specified minimum sea ice concentration (e.g., 15%) (km2).
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| Frequency of measurement |
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Daily
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| Spatial resolution |
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Concentration - 25 km;
Extent - 25 km.
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| Accuracy/precision required |
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Concentration: cold season ± 1%, melt season ± 5%;
(Currently available 4-7% in cold season and 10% in melt season.)
Ice Extent position - required accuracy ± 25 km (this is currently available).
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| Associated measurements |
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Ice surface temperature, radiation components, snow depth on ice, melt pond fraction, and sediment in ice.
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| Present status |
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Multi-frequency passive microwave data has been operational since 1978. 25 km gridded and ice products (FYI, MYI total ice/open water) are distributed on CD-ROMs by NSIDC (for SMMR and SSM/I). Radarsat Scansar and high resolution passive microwave data will permit mapping of leads and polynas. SAR only adds marginally to ice type mapping.
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| R and D needed |
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- Concentration and extent - Passive microwave mapping needs refinements for atmospheric effects, and algorithms for thin ice types need validating. Improvements are needed for SAR products in coastal areas and in marginal sea ice zones. Combine active and passive microwave data.
- Maintain and intercalibrate SSM/I data stream to insure consistent and continuous long-term time series of sea ice extent;
- Improve current retrievals to match required accuracy of ice concentration and extent.
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