Active microwave measurements of Arctic sea ice under summer conditions

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Abstract
Helicopter‐borne L‐C‐X‐Ku‐band radar backscatter data were acquired over test sites in the region about Saint Patrick Island, Northwest Territory, Canada, during June 1982. It is shown that the microwave response of sea ice is greatly influenced by summer, due to the many changes in properties of the snowpack and ice sheet. Hence the well‐documented winter‐and‐spring microwave response may not be extended into the summer season. In summer, the scattering cross sections of multiyear and first‐year ice become very similar, and their contrast is not only greatly reduced, but exhibits reversals in strength. During the early part of summer, discrimination was similar at all frequencies between 4 and 18 GHz with first‐year ice returns slightly stronger than those of multiyear ice. However, during peak melt, when the first‐year ice was extensively flooded and produced weaker returns than multiyear ice, operation at lower frequencies, especially L‐band, showed a 2–3 dB discrimination advantage. Angles greater than 25° from vertical provided the best contrast.