of factors act to reduce the accuracy of the retrievals, the most obvious being variations in the microwave signatures produced by a given surface type. For sea ice, the presence of snow, variations in salt and moisture content, the presence of melt ponds as well as variations in surface temperature will all produce strong variations in the microwave signature of a given ice type. New and thin ice in particular will often have a microwave signature closer to that of open water. This is normally because of its high salt content, not because of radiation being transmitted from the water through the ice—see sea ice emissivity modelling. The presence of waves and surface roughness will change the signature over open water. Adverse weather conditions, clouds and humidity in particular, will also tend to reduce the accuracy of retrievals. See also Arctic sea ice decline References External links High-resolution sea ice concentration charts derived from AMSR-E 89 GHz channel The Arctic ice sheet True color satellite map with daily updates. Sea ice Remote sensing Radiometry