JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 91, NO. C8, PAGES 9663-9681, AUGUST 15, 1986 Satellite Microwave and In Situ Observations of the Weddell Sea Ice Cover and its Marginal Ice Zone J. C. COMISO Laboratory for Oceans, NASA Goddard Space Fli•ihtCenter, Greenbelt, Maryland C. W. SULLIVAN Department of Biolo•Iical Sciences, University of Southern California, LosAn•ieles The radiative and physical characteristics of the Weddell Sea ice cover and its marginal ice zoneare studied using multichannel satellite passive microwave data in conjunction with in situ observations during the 1983 Antarctic Marine Ecosystem Research at the Ice Edge ZoneExperiment. Time series studies fromwinter through spring, using every other day observations fromthe Nimbus 7 scanning multichannel microwave radiometer, reveal significant spatial variability of the brightness temperatures of consolidated ice in winterand a recurring temporal •tndoftentimes larger spatial variability in spring. Therecurring effect in spring was found to bestrongly correlated withobserved surface air temperatu.res and is apparently associated with the cyclic changes in wetness of the snow coverof the ice while experiencing the freeze-thaw cycle. Analysis of scatter plotsof observed brightness temperatures from selected studyregions usingtwo or threefrequencies and/or polarizations shows that to effectively discriminate ice fromopen water within theicepack, a minimum of twochannels at different frequencies, preferably 18GHz and37GHz, is required. Serious problems associated withusing onlyone frequency, evenat two polarizations, (i.e.,37 GHz, and perhaps higher frequencies) havebeenobserved. Ice con- centrations derived from the sensor are compared with helicopter and ship observations, and results show consistency but a relatively low correlation coefficient partlydueto the quasi-qualitative nature of ttte in situ observations and uncertainties in ice emissivity in spring. The character and the northernmost extent of theice margin arequantified using radial plots of iceconcentration across theicepack andinto ice free ocean. Temporal changes in the ice margin structure are compared with ship data of physidal temperature, ice characteristics, wind,and weather. Studies of the mass balance of fresh waterand of biological features of themarginal ice zone areshown to benefit fromtime series information concerning the position of the ice •edge as derived from satellite remote sensing. 1. INTRODUCTION The adventof satellite remote sensing hasoffered intriguing opportunities to investigate,in good spatial and temporal detail, even the most remote or rarely visited areas o[ the earth's surface. The large extent of sea, icein polar regions, the difficulty and expenseof access, and the normally adverse weather conditions make satellite data almost indispensable for studiesrequiring global or large-scale ice cover character- isticsin theseregions. But the data would be usefulonly if interpretationsof the remotely sensed data are correct and/or verifiedby actual observations. Although someexperiments in the Arctic region, e.g., the Marginal Ice Zone Experiment, have been conducted partly to improve understanding a•nd utilization of satellite data, no experiment of a similar .nature has been undertakenin the Antarctic region. This makes it almost imperative that dataavailable fromrelated experi- ments be utilized to improve interpretation of Antarctic satel- lite data. This study is a follow-up to a previous investigation by Cotnisoet al. [1984] in which in situ observationsat the Weddell Sea by Americanscientists from the USSR ship Mik- hail Sotnovduring the period October 22 to November 3, 1981, were correlated with geophysical observations derived from satellite data. That studydemonstrated how two or more scanning multichannel microwave radiometer (SMMR) channels could be combined to derive ice concentration during the onset of spring and to discriminate ice free ocean Copyright1986 by the American Geophysical Union. Paper number 6C0261. 0148-0227/86/006C-0261 $05.00 with substantial weather effects from low ice concentration regions. In 1983 a group of American scientists from various ocean- ographic disciplines conducted the first of three cruises as part of the Antarctic Marine Ecosystem Research at the Ice Edge Zone (AMERIEZ) investigations recommended,by the Na- tional Academy ofSciences ina 1980 report. The experiment took place at about 37øW longitude and 62øS latitude from November 7 to December 3, providing an opportunity to in- vestigate a time period immediately followingthat reportedby Comiso et al. [!984]. The AMERIEZ project was motivated by a Polar Research Board committee report which identified the need for intensivestudy of the ice edge ecosystem of the southern ocean. It was hypothesized that the marginal ice zone is an area of high biologicalproductivity and serves as a boundary between two biological regions called pelagicand sea ice environment. Therefore the Studyrequires a compre- hensiveknowledgeof the sea ice cover, especially near the marginal ice zone. Because of this requirement, extensive ob- servations, both from on board the shipand from two helicop- ters, of the structure and characteristics of the ice in the vicin- ity of the experimental area were made. The helicopter plat- form allows large-scale observation of the ice pack and at the same time enables easy discrimination of the indvidual ice floes. These helicopter observations are useful for comparison with satelliteobservations especially because they cover areas comparable in size to severalsatellite fields of view. Physical and chemical analysis of 13 ice cores from some representative ice floes alsoprovide a stronger basis for properinterpretation of the satellite signature, which is affected by variousparame- tersincluding wetness in snow cover, salinity, a•nd melt pond- ing at this time of the year. Winter data were also analyzed 9663