The age of the sea ice is usually a distinction between first-year
and multiyear ice. Multiyear sea ice is usually thicker, has more ridges,
and can be more of a hinderance to ship travel than first-year ice.
Microwave remote sensing studies have shown that first-year sea ice has a
higher emissivity at the 1.55 cm wavelength than multiyear ice, thus
making it possible to distinguish between different ice ages from
satellites. Ice age can also be qualitatively determined using visible,
infrared and radar wavelengths from satellites.
