Effective Monitoring for marine debris after Great East Japan Earthquake by using spaceborne synthetic aperture radar

摘要

The Great East Japan Earthquake occurred at March 11, 2011 and caused massive tidal wave. The tsunami swept away a large quantity of rubble and vessels to the sea and they become so-called marine debris. To assess damage situation and protect marine environment, it is essentially required to investigate the status of those marine debris. The technique based on spaceborne synthetic aperture radar (SAR) can be a strong candidate to achieve this ultimate goal, because of its wide observation area and higher resolution with flexible operability: regardless of the day and night and regardless of the weather. We have monitored marine debris on huge amount of spaceborne SAR imagery right after the great disaster and investigated an effective observation of marine debris to predict future direction. In this paper, we firstly define three types of debris as large debris, small debris, and cluster by considering how marine debris looks like on the SAR imagery. Then, an automatic but accurate detection and classification of a large amount of debris on SAR imagery is proposed. Based on those results, resolution and swath width for efficient marine debris monitoring are obtained. Velocity of marine debris is additionally estimated from multi-temporal SAR images to derive optimum swath width.