Sea ice monitoring and modelling in a small Bay

摘要

In February 2002, a drastic sea ice dynamic event took place in Pärnu Bay, a small basin of 15 km across in the Gulf of Riga, Baltic Sea. The fast ice in this event was broken into small blocks by a strong wind and moved together with the pack ice on 5 February. The whole ice cover remained immobile under southwest wind during 6–13 February. During 13–14 February, part of the ice cover drifted out of the basin under mild northwest wind, about half of the basin opened and in the other side heavy rubble formation occurred. The thickness of the fast ice was 20–40 cm and pack ice about 5–15 cm, and the highest wind speed was about 20 ms, unusual combination necessary for the event. In this paper, we applied a fine resolution ice model to investigate the sea ice dynamics. The numerical experiments show that the heavy deformation process of the ice cover caused little change of the compressive strength but noticeably reduced the shear strength. MODIS (Moderate Resolution Imaging Spectrometer) images on board of satellites Aqua & Terra were used to describe the ice conditions in the Gulf of Riga, the Baltic Sea during winters 2001–2004. Ice conditions are very variable in the Gulf dependant on severity of winter. A simple method of the ice type classification was developed specifically for coastal sea and applied to MODIS 500 meter reflectance images by using Spectral Angle Mapper (SAM). Maps of ice types in the Gulf of Riga with spatial resolution of 500 meters were produced for several cloud-free situations during winters 2002/2003 and 2003/2004. The classified sea ice maps were verified by repeated field surveys on different stages of ice development.