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Oil spills on ALOS PALSAR and Envisat ASAR images

Leonid Mitnik(1)

(1) Pacific Oceanological Institute, FEB RAS, 43 Baltiyskaya Street, 690041 Vladivostok, Russian Federation

Abstract

The Asian marginal seas and especially their coastal zones are strongly impacted by oil pollution. SAR seems to be one of the most suitable instruments for spill detection, in particular, to fight against illegal discharges and provide information about the oil spill, its spreading and the drift forecasting in a case of accident independently on darkness and cloudiness. Oil spills and natural monomolecular films (slicks) modify seawater viscosity and produce a strong damping impact on short waves measured by SAR. As a result spills and slicks appear as dark patches and bands on the SAR images. Their radar contrast against the surrounding waters depends not only on wind and wave conditions but on SAR parameters such as wavelength (PALSAR L-band or Envisat/ERS/RADARSAT C-band), polarization (HH, HV, VH, VV), incidence angle. Cases of easy and ambiguous detection of oil spills on Envisat ASAR and ALOS PALSAR images of different regions of the Pacific Ocean are considered. The main attention is given to analysis of SAR images of oil spill from tanker "Hebei Spirit" in the Yellow Sea on 7 December 2007. More than 10000 tons of crude oil released into the sea approximately 8 km off the South Korea coast, 150 km southwest of Seoul. SAR images were acquired on 9 December (L-band PALSAR), 11 December (C-band ASAR, wide-swath mode at 01:40 UTC, VV-polarization and RADARSAT, 09:31 UTC, wide-swath mode W2, HH-polarization and L-band PALSAR at 13:46 UTC), 14 December (C-band RADARSAT, wide-swath mode at 01:47 UTC, VV-polarization) and 15 December (C-band ASAR, wide-swath mode at 21:30 UTC, HH-polarization). Ancillary data are used to interpret SAR signatures caused by oil spill as well as by oceanic and atmospheric phenomena. Analysis of the images shows that C-band radar contrast of oil spills against the surrounding waters exceed significantly L-band contrasts that confirms essentially the previous results.

 

 

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