Sea ice concentrations, derived from passive microwave satellite sensor measurements, provide today reliable ice information on global scal. The current operational Special Sensor Microwave/ Imager (SSM/ I ) operating as part of the U. S. Defence Meteorological Satellite Program ( DMSP ), was first launched in june 1987 into a polar orbit. Due to the different emissivities of water and different ice types it is possible to obtain ice concentrations and ice fractions using suitable algorithms. During the winter time, when the overlying snow on sea ice is dry, concentrations can be retrieved to an accuracy of +/- 7%. In the summer, when surface melt is predominant, melt features appear on the ice in form of puddles or melt holes. The extent of melt features depends very much on the host ice type. In general the ice can be calssified as first year ice or old ice.The amount of water accumulated in melt features could be as high as 90% on first year ice and possibly up to 50% on old ice can lead to significant algorithm retrieval errors of ice concentrations. In order to obtain accurate melt feature concentrations a line scan camera mounted on a helicopter can provide areal coverage. Preliminary analysis of the camera data indicates that water, ice, puddles and refrozen puddles could be quantitatively separated. On 7 an 8 August 1990, based on two line scan camera flights, the ice concentration was 67% with 14% melt puddles and 40% ice concentrations with 52% melt puddles, respectively.The rest open water. The SSM/ I ice concentration for the same locations wer 46% and 35% respectively. The SSM/I ice concentrations can be compared directly to the line scan camera values. The difference in ice concentrations observed of 21 and 5% respectively can be explained due to differences in areal coverage by the two sensors. The line scan camera covered only about 6% of the gridpoint area covered by the SSM/I which consist of an area of 625 Km2 , based on these measurements, the actual SSM/I ice concentration should be 86% and 65% respectively. The method of using a line scan camera shows great promise of providing a correction to the SSM/I algorithm under summer conditions. With further experiments the camera measurements will also provide a better understanding of the melt feature life cycle on old ice.
AWI Organizations > Climate Sciences > Climate Dynamics
AWI Organizations > Climate Sciences > Sea Ice Physics