| Summary: | This paper describes the results of the recent field tests conducted in the spring of 2002 and 2003 inf the Archipelago Sea. The aim of these tests was to study the performance of the following new innovations: the modified ice vibrating unit-the use of pneumatic air to develop artificial flow field under ice. The operatio of the vibrating system was improved, based on first field in 2001. The tests showed the modification made since the first field trials, which had been successful. Less ice than before drifted inside the vibrating unit and the oil recovery chamber of the vessel. Therefore, less small ice cubes were lifted up by the brush belt. The capacity of the screw conveyor belt was adequante for placing the ice cubes back into the sea. The main idea of the use of pneumatic air under ice was to pump a large amount of air under the ice level, thus creating a vertically rising bubble curtain. This curtain will in turn raise a large amount of water and form a vertical plume with significant flow velocities, When meeting the ice level, the flow will turn radially, therefore a strong horizontal flow can be created under the ice to remove trapped oil. Different production rates of air were pumped through the underwater outlet situated at depths of 10, 20 and 30 m. The velocity field was measured on the ice through the predrilled holes. An underwater ROV was used to measure the width of the rising bubble curtain by a Sonar device. The device was operated by the Finnish Coast Guard from the support vessel "Tursas". The oil recovery vessel "Halli" acted as a support platform for the execution.
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