Salamina Oil spill from satellite (15/9/2017)  

Salamina Oil spill from satellite (15/9/2017)

MRSG analyzed the Sentinel-1 satellite image (Copernicus-ESA) for detecting the possible polluted area near the island of Salamina in the Saronic Gulf. The 45-year-old vessel, Agia Zoni II, was carrying 2,500 tonnes crude oil. The oil slick caused on Sunday (10/9/2017) when crude oil tanker “Agia Zoni II” sank. The slick 5 days after the accident reached a region from Piraeus to Ag. Kosmas (located with red arrows).

Synthetic Aperture Radar (SAR) images are ideal for monitoring oil pollution in the sea. SAR is an active microwave sensor, which captures two dimensional images. The brightness of the captured image is a reflection of the properties of the target-surface. The possibility of detecting an oil spill in a SAR image relies on the fact that the oil film decreases the backscattering of the sea surface resulting in a dark formation that contrasts with the brightness of the surrounding spill-free sea. Spaceborne SAR sensors are extensively used for the detection of oil spills in the marine environment, as they are independent from sun light, they are not affected by cloudiness, they cover large areas and are more cost-effective than air patrolling. There are different mechanisms responsible for the sea surface radar backscattering, which strongly depend on the incidence angle of the radar sensor. In a quite large range of angles, approximately from 20º to 50º, the main agent of radar backscattering are the wind-generated short gravity-capillary waves. The oil film has a dampening effect on these waves locally decreasing the backscattering.

It is implicitly assumed that a light wind field exists in order to activate short gravity- capillary waves. The minimum wind speed is in fact depending on the frequency of observation and the incidence angle. The most common radar sensors on board of operational satellites are using the C band. In this frequency range, a minimum wind field of 2–3 m/s creates sufficient brightness in the image and makes the oil film visible. On the other hand, when the wind speed is too high, it causes the spill to disappear. First, because the short waves receive enough energy to counterbalance the dumping effect of the oil film. Then, when the sea-state is fully developed, the turbulence of the upper sea layer may break and/or sink the spill or a part of it. Several man made and natural ocean phenomena damp the wind generated short gravity – capillary waves. For this reason, some areas appear dark on SAR imagery in contrast to the surrounding sea.


Topouzelis and S. Singha, 2016, CHAPTER 6, Oil Spill Detection Using Space-Borne Sentinel-1 SAR Imagery, Oil Spill Science and Technology, 2nd Edition by Mervin Fingas, Publisher: Gulf Professional Publishing, Release Date: November 2016, ISBN: 9780128110966

Topouzelis, D. Tarchi, M. Vespe, M. Posada, O. Muellenhoff and G. Ferraro, 2015, Chapter: 13, Detection, Tracking, and Remote Sensing: Satellites and Image Processing (Spaceborne Oil Spill Detection), Handbook of Oil Spill Science and Technology, Publisher: John Wiley & Sons, Editors: Merv Fingas

Topouzelis, 2008, “Oil spill detection by SAR images: Approaches and Algorithms”, Invited paper for the special issue: Synthetic Aperture Radar (SAR), SENSORS Journal (open access), no. 8, pp. 6642-6659.