The Operational Sea Ice Mapping Using ERS SAR Images in the Baltic Sea

Abstract

A short overview about the experiences gathered in the operational sea ice mapping during the ESA AO project OSIC in 1993-1995 and the description of the current status of ERS SAR based sea ice mapping in the Baltic Sea will be presented. The Finnish Ice Service received together c. 250 Fast Delivery Low Resolution ERS-1 SAR images during the project and has bought significant amount of ERS SAR scenes each winter since then. The Gulf of Bothnia and the Gulf of Finland were selected as the experimental area for ERS-1 images. The images were used in routine ice service activities and most of them were delivered to the icebreakers at sea. To validate the visual interpretation of the data, SAR images were compared with AVHRR data and ground truth. Also field campaigns were carried out. During these years the possibilities of the automated sea ice mapping were also consistently examined. The current version of the sea ice mapping algorithm produces fully automatically an ice chart with five qualitative ice categories including open water. The classification algorithm is bivariate and utilises the wavelet decomposition in several resolution levels as its starting point. From this decomposition two variables are constructed, intensity and the wavelet coefficient based local roughness texture measure. Through this measure the structure of the sea ice fields has been taken into account. The decision of the occurrence of open water is made for each image separately. Otherwise the occurrence of the ice class is assumed and the ice categories in the resulted ice map are hence only relative. It can be said that ERS SAR, all though not designed for operational use has become operational in sea ice monitoring. It diversifies the sea ice information sources and in some difficult situations can give highly valuable, otherwise inaccessible, very detailed knowledge about ice conditions.

Keywords: ERS-1, SAR, ice mapping, classification, Baltic Sea

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry