Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 8 4 2008 10.5194/acpd-8-14819-2008 http://www.atmos-chem-phys-discuss.net/8/14819/2008/ http://www.atmos-chem-phys-discuss.net/8/14819/2008/acpd-8-14819-2008.html http://www.atmos-chem-phys-discuss.net/8/14819/2008/acpd-8-14819-2008.pdf 14819 14839 2008-08-01 Detection of ship tracks in ATSR2 satellite imagery E. Campmany campmany@atm.ox.ac.uk R. G. Grainger S. M. Dean Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, UK National Institute of Water and Atmospheric Research Ltd, Wellington, New Zealand Ships modify cloud microphysics by adding cloud condensation nuclei (CCN) to a developing or existing cloud. These create lines of larger reflectance in cloud fields that are observed in satellite imagery. Ship tracks are most frequently seen off the west coast of California, and the Atlantic coast of both west Africa and south-western Europe. In order to automate their detection within the Along Track Scanning Radiometer 2 (ATSR2) data set an algorithm was developed and integrated with the Global Retrieval of ATSR Cloud Parameters and Evaluation (GRAPE) processing chain. The algorithm firstly identifies intensity ridgelets in clouds which have the potential to be part of a ship track. This identification is done by comparing each pixel with its surrounding ones. If the intensity of three adjacent pixels is greater than the intensity of its neighbours, then it is classified as a ridgelet. These ridgelets are then connected together, according to a set of connectivity rules, to form tracks which are classed as ship tracks if they are long enough. The algorithm has been applied to two years of ATSR2 data. A month of results have been compared with other satellite datasets to validate the algorithm. There is a high ratio of false detections. 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