The Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E) instrument on the NASA EOS Aqua satellite provides global passive microwave measurements of land, ocean, and atmospheric variables for the investigation of water and energy cycles.

This Level-3 gridded product (AE_SI12) includes brightness temperatures (TBs) at 18.7 through 89.0 GHz, sea ice concentration, and snow depth over sea ice. Data are mapped to a polar stereographic grid at 12.5 km spatial resolution. Sea ice concentration and TBs include daily ascending averages, daily descending averages, and daily averages; snow depth over sea ice data is a five-day running average. Data are stored in HDF-EOS format.

The full suite of AMSR-E sea ice products includes brightness temperatures at 6.25 km, 12.5 km, and 25 km resolution; sea ice concentration at 12.5 km and 25 km resolution, sea ice temperature at 25 km resolution; and snow depth over sea ice at 12.5 km resolution.

Theory of Measurements:
Sea ice concentration products are used to understand the spatial characterization of sea ice cover and to calculate sea ice extent and area for time series analyses and process studies in the Arctic and Antarctic. Passive microwave data are particularly useful for sea ice studies because of the relatively high contrast in emissivities between open water and sea ice. This contrast is frequency-dependent; contrast increases with decreasing channel frequency. In most algorithms, atmospheric effects are assumed constant. The satellite-received radiation, expressed as a brightness temperature (TB), is as follows (Cavalieri and Comiso 2000):

TB = TBWCW + TBICI [1]
Where:
TBW = TB of open water
TBI = TB of sea ice
CW = fraction of open water within instrument field-of-view
CI = fraction of sea ice (ice concentration) within instrument field-of-view
Ice concentration (CI), corresponding to an observed TB over a sea ice-covered region (TB), is derived as follows:
CI = (TB - TBW) / (TBI - TBW) [2]

The AMSR-E sea ice algorithms use this equation, but the channels and methods to derive CI are different. Values of TBW, TBI, and TB all include contributions from the intervening atmosphere. TBI varies spatially because of spatial changes in emissivity and temperature of ice, while TBW is constant for open water within the ice pack.

Derivation Techniques and Algorithms:
The 12.5 km sea ice concentration product is generated using the Enhanced NASA Team (NT2) algorithm ((Markus and Cavalieri 2000) for both the Arctic and the Antarctic. Previous product versions employed the Bootstrap Basic Algorithm (BBA, Comiso 1995) for the Antarctic; now the BBA is used in the sea ice concentration difference (NT2-BBA) field for both hemispheres.

If you have any comments, please E-mail the National Ice Center Liaison