The influence of the atmosphere on the remote sensing of sea ice using passive microwave radiometers

The effects of weather systems on sea-ice concentration retrievals using passive microwaves are investigated because significant errors in estimating short-time variations and climatological concentration trends occur due to clouds and water vapor. For the assessment of these weather effects, the atmospheric parameters integrated water vapor content (W) and cloud liquid water path (LWP) are derived from radiosonde ascents measured in the pack-ice area of the Weddell Sea/Antarctica in 1992. Using a microwave radiative transfer model and typical surface emissivities, brightness temperatures are calculated from the radiosonde ascents. The first-year, multiyear and total sea-ice concentrations are calculated using the NASA team sea-ice algorithm for the SSM/I radiometer (Special Sensor Microwave/Imager). Thus the ice concentration changes depending on surface composition (open ocean, first-year ice, multiyear ice) and the values of LWP and W are modelled. Modelled atmospheric effects and measured sea-ice concentration changes, the latter being derived from SSM/I radiometer data, are in good agreement both geographically and quantitatively in areas with large frontal cloud structures, as identified using infrared satellite data. A method is presented for a large-scale estimation of the necessary parameters LWP and W over sea ice. Using these results the derived sea-ice concentrations can be corrected for the modelled atmospheric effects.