Abstract
Countless numbers of people lost their lives at Europe’s southern borders in recent years in the attempt to cross to Europe in small rubber inflatables. This work examines satellite-based approaches to build up future systems that can automatically detect those boats. We compare the performance of several automatic vessel detectors using real synthetic aperture radar (SAR) data from X-band and C-band sensors on TerraSAR-X and Sentinel-1. The data was collected in an experimental campaign where an empty boat lies on a lake’s surface to analyse the influence of main sensor parameters (incidence angle, polarization mode, spatial resolution) on the detectability of our inflatable. All detectors are implemented with a moving window and use local clutter statistics from the adjacent water surface. Among tested detectors are well-known intensity-based (CA-CFAR), sublook-based (sublook correlation) and polarimetric-based (PWF, PMF, PNF, entropy, symmetry and iDPolRAD) approaches. Additionally, we introduced a new version of the volume detecting iDPolRAD aimed at detecting surface anomalies and compare two approaches to combine the volume and the surface in one algorithm, producing two new highly performing detectors. The results are compared with receiver operating characteristic (ROC) curves, enabling us to compare detectors independently of threshold selection.
Highlights
The ongoing humanitarian crisis in the Mediterranean Sea still sees refugees risking their lives in small rubber inflatables in their desperate attempt to flee from terror, rape, and persecution
We provide a short introduction to detection theory and to receiver operating characteristic (ROC) curves which is the visualization method we chose for our results
We compare the performance of different vessel detection systems for the detection of a small rubber inflatable using TerraSAR-X and Sentinel-1 data
Summary
The ongoing humanitarian crisis in the Mediterranean Sea still sees refugees risking their lives in small rubber inflatables in their desperate attempt to flee from terror, rape, and persecution. Human traffickers pack these rubber inflatables with people and let them debark on a—at least—250 km journey to Europe. We want to test and validate the detection capabilities of satellite-based imaging radar to contribute to search and rescue efforts. Radar (SAR) database of such 12 m × 3.5 m × 0.5 m (l/w/h) rubber inflatables using a lake as a test-bed. The study showed that the identification capabilities do greatly depend on several different sensor and scene parameters such as the vessel’s speed and heading and the local wind conditions
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