SAR-based Ship Monitoring: Advanced Methodologies with Medium Resolution Images (from WSM ASAR to EWS/IWS S1 Mission)
Longépé, Nicolas1; Hajduch, Guillaume1; Pelich, Ramona1; Habonneau, Jerome2; Lebras, Jean-Yves1
1CLS, FRANCE; 2Télécom Bretagne, FRANCE

SAR-based vessel detection has wide range of applications (traffic safety, fisheries monitoring, association with oil discharge, border surveillance...) with very diverse requirements in terms of detection performance, revisit time, etc. The improvement of the ship monitoring with SAR image is generally not compatible with a systematic monitoring of large area with wide swath and medium resolution products.

The purpose of this paper is twofold:
1) to provide a comprehensive methodology for benchmarking vessel detection rate by using an automatic integration of coastal AIS messages. The performance of coastal AIS reception needs to be assessed a priori if used for ship detection validation (limit of VHF range, discontinuity, saturation in the case of dense traffic, geographically heterogeneity ...). As a result, a particular attention has been paid to the modelling of the receiving capabilities of each available AIS station, this modelling being then used into the quantitative assessment of the SAR-based detection rate. To demonstrate this validation protocol, about 1000 ship detection reports from ASAR images (mostly WSM acquired from end 2010 to April 2012) have been automatically combined with coastal AIS messages.
2) The estimation of the characteristics of the detected vessel is generally based on the estimation of the geometric shape of the detected echo. On the other hand it has been shown that the Radar Cross Section (RCS) of the vessels may be expressed as a function of the ship length [Vachon et al. 1997]. Thanks to our extensive database with thousands of SAR - AIS matching, we present here both an improvement of this RCS model and its application to the sub-pixel estimation of the vessels' length.

The forthcoming Sentinel-1 mission will be equipped with medium resolution SAR sensor that will be used for systematic monitoring of European Waters: the automatic validation of SAR-based ship detection products and an advanced methodology for sub-pixel ship characterization (vessel length) are two requisites for an efficient maritime surveillance with Sentinel-1.

This study is partially funded by the European Commission under Framework Programme 7 (FP7) DOLPHIN project and by ESA under the MARISS project.

Vachon, P.W., J.W.M. Campbell, C.A. Bjerkelund, F.W. Dobson, and M.T. Rey. < Ship Detection by the RADARSAT SAR: Validation of Detection Model Predictions >. Canadian Journal of Remote Sensing/Journal canadien de teledetection 23, n. 1, 1997