The interaction of microwaves with sea ice
The sea ice pack in the polar regions plays a fundamental role in global climate as the boundary layer separating the ocean and atmosphere in these regions. Due to its vast extent, the physical properties of the sea ice pack are often studied via electromagnetic remote sensing from satellites and airplanes, in the microwave regime. In this work we give an overview of ongoing investigations of the interaction of microwaves with sea ice. This interaction is particularly interesting in the case of sea ice, which is a composite of pure ice with random brine and air inclusions, whose geometry can depend dramatically on temperature. These investigations include finding a series of bounds on the effective complex permittivity ε* of sea ice, under constraints on the microgeometry, such as fixed brine volume. In particular, we describe some rather tight bounds on ε* which incorporate the geometrical constraint that for temperatures colder than the percolation threshold, Tc ≈ –5°C, the brine phase is contained in separated inclusions. These bounds fit actual data on ε* at 4.75 GHz quite closely. We also describe how this series of bounds, which are derived in the quasistatic limit, break down when compared with data taken in the 26.5–40.0 GHz range. Finally, we briefly discuss some preliminary results of backscatter experiments we conducted at C band (5.3 GHz) on first year sea ice in the Weddell Sea, Antarctica, during the austral winter of 1994.
Key wordsmicrowaves complex permittivity sea ice matrix-particle composites
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