Satellite microwave and in situ observations of the Weddell Sea ice cover and its marginal ice zone

Abstract

The radiative and physical characteristics of the Weddell Sea ice cover and its marginal ice zone are studied using multichannel satellite passive microwave data in conjunction with in situ observations during the 1983 Antarctic Marine Ecosystem Research at the Ice Edge Zone Experiment. Time series studies from winter through spring, using every other day observations from the Nimbus 7 scanning multichannel microwave radiometer, reveal significant spatial variability of the brightness temperatures of consolidated ice in winter and a recurring temporal and oftentimes larger spatial variability in spring. The recurring effect in spring was found to be strongly correlated with observed surface air temperatures and is apparently associated with the cyclic changes in wetness of the snow cover of the ice while experiencing the freeze‐thaw cycle. Analysis of scatter plots of observed brightness temperatures from selected study regions using two or three frequencies and/or polarizations shows that to effectively discriminate ice from open water within the ice pack, a minimum of two channels at different frequencies, preferably 18 GHz and 37 GHz, is required. Serious problems associated with using only one frequency, even at two polarizations, (i.e., 37 GHz, and perhaps higher frequencies) have been observed. Ice concentrations derived from the sensor are compared with helicopter and ship observations, and results show consistency but a relatively low correlation coefficient partly due to the quasi‐qualitative nature of the in situ observations and uncertainties in ice emissivity in spring. The character and the northernmost extent of the ice margin are quantified using radial plots of ice concentration across the ice pack and into ice free ocean. Temporal changes in the ice margin structure are compared with ship data of physical temperature, ice characteristics, wind, and weather. Studies of the mass balance of fresh water and of biological features of the marginal ice zone are shown to benefit from time series information concerning the position of the ice edge as derived from satellite remote sensing.