ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-9-1899-2009 Automatic detection of ship tracks in ATSR-2 satellite imagery Campmany E. 1 2 Grainger R. G. 1 Dean S. M. 1 3 Sayer A. M. 1 Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford OX1 3PU, UK now at: NASA Goddard Institute for Space Studies, New York, USA now at: National Institute of Water and Atmospheric Research Ltd, Wellington, New Zealand 18 03 2009 9 6 1899 1905 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/9/1899/2009/acp-9-1899-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/9/1899/2009/acp-9-1899-2009.pdf

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. An algorithm has been developed to automate the detection of ship tracks in Along Track Scanning Radiometer 2 (ATSR-2) imagery. The scheme has been integrated into 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 their 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 ATSR-2 data. Ship tracks are most frequently seen off the west coast of California, and the Atlantic coast of both West Africa and South-Western Europe. The global distribution of ship tracks shows strong seasonality, little inter-annual variability and a similar spatial pattern to the distribution of ship emissions.

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