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Sea ice classification using ASAR Alternating Polarisation images

Stein Sandven(1), Kjell Kloster(1), Vitaly Yu. Alexandrov(2) and Natalia Y. Piotrovskaya(2)

(1) NANSEN ENVIRONMENTAL AND REMOTE SENSING CENTER, Thormohlensgate 47, N-5006 Bergen, Norway
(2) Nansen International Env. and Remote Sens, Vasilievsky Island 14th Line, 7A, 199034 Saint-Petersburg, Russian Federation

Abstract

Sea ice classification in single polarisation SAR images has been attempted using various methods since the beginning of the ERS programme, but the classification results tend to be case specific and not generally applicable. Robust classification methods that can provide useful results under varying sea ice and ocean conditions are lacking so far. The new generation SAR satellites have capability to deliver images in several polarisations. This gives improved possibility to develop sea ice classification algorithms. In this study Alternating Polarisation images from ENVISAT ASAR have been analyzed over sea ice areas in different parts of the European Arctic and the Caspian Sea. The most promising results suggest to use HH and VV polarisation to discriminate ice and open water at high incidence angles (swath IS5 – IS7). Since open water backscatter is very sensitive to wind speed, it is necessary to analyse a larger data set covering a wide range of wind speeds. Also classification of multiyear, firstyear and thin ice types can be improved by use of polarisation data, but more studies are needed to establish which combination of co-and cross-polarisation are optimal for ice type classification. In the Marginal Ice Zone (MIZ), the standard discrimination between multiyear, firstyear and different forms of new ice is often meaningless due to the wave action on the ice cover. In SAR classification, it is more useful to define a specific class for the MIZ, characterised by many small floes. The study has looked into the possibility to discriminate between level ice and ridged ice by use of C-band cross-polarization, but this requires validation by dedicated field experiments including aircraft surveys. As a result of the International Polar Year (2007-2008) there will many new in situ observations of sea ice available, and these will be used in the validation of SAR ice classification algorithms. The goal of this work is to establish more robust classification algorithms that can be used for Sentinel-1 in operational sea ice monitoring.

 

Workshop presentation

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