Remote sensing of sea ice surface thermal states under cloud cover

It is necessary to know sea ice surface thermal states under cloud cover to evaluate cloud effects in the overall climatic feedback mechanisms in polar regions. The challenge is that traditional methods using radiometers such as AVHRR for surface temperature measurements fail under cloudy conditions. The authors present a new method combining C-band radar data to study sea ice surface temperature change and visible/infrared radiometer data to identify clouds. From laboratory experiments, the authors show that C-band radar backscatter is sensitive to sea ice surface thermal states. This relationship is utilized to develop the methodology for the sea ice surface temperature study. The authors present an example with ERS-1 SAR data, AVHRR data, and field experiment measurements over first-year and multi-year sea ice in the Canadian Arctic Archipelago to illustrate the methodology. In this example, SAR data show an increase in sea ice surface temperature, caused by an excess in the surface heat balance under cloud cover. The method is applicable to Arctic first-year ice. For Antarctic sea ice, this method is particularly appropriate since the Antarctic ice cover consists of vast regions of first-year ice where salinity levels are generally higher than those of Arctic sea ice of similar age and structure