Oil Spill Surveillance and Tracking with Combined use of SAR and Modis Imagery: A Case Study

Abstract

The use of satellite remote sensing for oil spills detection has been attempted, traditionally, with synthetic aperture radar (SAR) sensors. These sensors are the most suitable instruments to the detection of slicks, since they damp strongly short waves measured by SAR and oil spills appear as a dark patch on the SAR image. However, SAR systems do not offer the required temporal acquisition rate of the same area, to guarantee the possibility to monitoring large oil spill movement on the sea. We propose the use the Modis (Moderate Resolution Imaging Spectroradiometer) images acquired in sun glint conditions to reveal smoothed regions such as those affected by oil pollution. In this work we present a case study, in the Mediterranean Sea near the French coast, in which we have applied this methodology to a large oil spill detected on a SAR image of the 8th July 2002. Using two Modis acquisition in the same day, one by Modis/TERRA 20 minutes later the ERS2-SAR acquisition and the other by Modis/AQUA 80 minutes later the first Modis acquisition, we show that it is possible to surveil the oil spill in its movement towards north-west. Wind speeds and directions at 10 m above the sea surface were retrieved using the semi- empirical backscatter model CMOD4 on the SAR image, and utilized to track the movement of oil spill. Surface wind vectors predicted by the meteorological ECMWF model were exploited as guess input to SAR wind inversion procedure. The comparison between Modis images and the predicted position of the oil spill show an adequate agreement.